Articles, systems, and methods for electrochemically generating chemical products

Abstract

Certain aspects of the present disclosure generally relate to systems for electrochemically generating compounds, such as for generating hydrogen peroxide or other applications. In some cases, the system may include an electrode comprising a substrate comprising carbon-containing nonwoven fibers, PTFE particles on the substrate, and / or an active material, such as carbon particles, on the substrate and / or on the PTFE. In some embodiments, the system may generate a two-phase solution and / or flow the two-phase solution over and / or through at least a portion of an electrode. Some systems using the electrode structures and / or two-phase solutions may facilitate the formation of a three-phase interface, which may facilitate the electrocatalytic production of certain compounds at the three-phase interface. Yet other aspects relate to, among other things, methods of making and / or using the systems.

Description

[0001] Related applications

[0002] This application is a continuation-in-part of U.S. Patent Application No. 18 / 365,901, filed August 4, 2023, entitled “Articles, Systems, and Methods for Electrochemically Generating Chemical Products”; U.S. Patent Application No. 18 / 365,934, filed August 4, 2023, entitled “Operation Method of a System for Electrochemically Generating Chemical Products”; U.S. Patent Application No. 18 / 365,956, filed August 4, 2023, entitled “Modified Electrode and Method of Manufacturing the Same”; and U.S. Patent Application No. 18 / 365,962, filed August 4, 2023, entitled “Two-Phase Solution for Electrochemically Generating Chemical Products”, each of which is incorporated herein by reference in its entirety for all purposes. Technical Field

[0003] This disclosure generally relates to systems and methods for the electrochemical generation of compounds (e.g., hydrogen peroxide). Background Technology

[0004] Electrochemical systems are used in a wide range of applications, from electrocatalytic chemical generation to energy storage. However, many of these systems operate with relatively low efficiency due to side reactions, slow kinetics of the target reaction at the relevant electrode structures, and / or slow mass transport that inhibits the rate of the target reaction. Furthermore, the systems and related methods used to generate target chemicals may not be designed for continuous and efficient operation, for example, due to the formation of precipitates in the system that can poison or otherwise block active sites on the electrode surface and / or cause rupture of the electrode pore structure. Therefore, improved electrode structures, systems, and methods are needed. Summary of the Invention

[0005] This disclosure generally relates to systems and methods for the electrochemical generation of compounds (e.g., hydrogen peroxide). In some cases, the subject matter of this disclosure relates to interrelated products, alternative solutions to specific problems, and / or multiple different uses of one or more systems and / or articles.

[0006] Some aspects involve electrodes. In some cases, the electrode comprises a nonwoven substrate containing carbon fibers; a first hydrophobic polymer formed on at least a portion of the nonwoven substrate; and a catalytic layer comprising a second hydrophobic polymer and a carbon-containing active material, said active material having a surface area greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g, and formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer. In some embodiments, the electrode comprises a nonwoven substrate containing carbon fibers; and a plurality of hydrophobic regions distributed on at least a portion of the nonwoven substrate, wherein at least a portion of the plurality of hydrophobic regions is at least partially surrounded by hydrophilic regions. In some embodiments, the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the first and / or second hydrophobic polymers comprise PTFE powder and / or PTFE micropowder.

[0007] In some embodiments, the porosity of the nonwoven substrate is at least 0.85. In some embodiments, the thickness of the nonwoven substrate is greater than or equal to 0.75 mm. In some embodiments, the thickness of the nonwoven substrate is greater than or equal to 2 mm. In some embodiments, this thickness is an uncompressed thickness. In some embodiments, the nonwoven substrate has an uncompressed thickness, a compressed thickness when the substrate is incorporated into an electrochemical system, and the ratio of uncompressed thickness to compressed thickness is greater than or equal to 1.05 and less than or equal to 2.0. In some embodiments, the nonwoven substrate comprises elemental carbon. In some embodiments, the nonwoven substrate comprises carbon felt. In some embodiments, the nonwoven substrate is carbon felt. In some embodiments, the average maximum cross-sectional size of the PTFE particles does not exceed 25 micrometers. In some embodiments, the PTFE particles form multiple hydrophobic regions. In some embodiments, the multiple hydrophobic regions comprise a hydrophobic polymer. In some embodiments, the hydrophobic polymer is PTFE. In some embodiments, the hydrophilic regions comprise carbon. In some embodiments, the PTFE particles permeate at least 5% of the thickness of the nonwoven substrate. In some embodiments, the PTFE particles permeate the entire thickness of the nonwoven substrate. In some embodiments, the first and / or second hydrophobic polymer comprises PTFE derived from a dispersion and / or emulsion. In some embodiments, the first and / or second hydrophobic polymer comprises a mixture of PTFE powder and / or micropowder and / or PTFE derived from a dispersion and / or emulsion.

[0008] Some aspects relate to systems. In some cases, the system includes an electrode comprising a nonwoven substrate containing carbon fibers; and a plurality of hydrophobic regions distributed on at least a portion of the nonwoven substrate, wherein at least a portion of the plurality of hydrophobic regions is at least partially surrounded by hydrophilic regions. In some embodiments, the system includes an electrode comprising a nonwoven substrate containing carbon fibers; a first hydrophobic polymer formed on at least a portion of the nonwoven substrate; and a catalyst layer comprising a second hydrophobic polymer and a carbon-containing active material, the active material having a surface area greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g, and formed on at least a portion of a nonwoven substrate and / or a first hydrophobic polymer. In some embodiments, the electrode is configured to electrogenerate the compound. In some embodiments, the electrode is configured to electrogenerate hydrogen peroxide. In some embodiments, the system is configured to operate with a Faraday efficiency of greater than or equal to 95% in generating hydrogen peroxide.

[0009] Some aspects involve electrodes. In some cases, the electrode comprises a nonwoven substrate containing carbon fibers; a first hydrophobic polymer formed on at least a portion of the nonwoven substrate; and a catalyst layer comprising a second hydrophobic polymer and a carbon-containing active material, wherein when the content is greater than or equal to 0.001 M and less than or equal to 4.8 M OH... - When configured in a system containing 0.001 M H₂O₂ or greater and less than or equal to 2 M H₂O₂ and having an average temperature of at least 35 °C, the electrode is configured to operate at a speed of 300 mA / cm². 2 Hydrogen peroxide is electrochemically generated at a current density of less than or equal to 1.5 V for a duration of greater than or equal to 1,000 hours. In some embodiments, OH... - The equilibrium ion is an alkali metal. In some implementations, OH... - The equilibrium ion is Na. + and / or K + In some implementations, OH in the system + The molecular ratio of H2O2 to H2O2 is approximately 2:1.

[0010] Some aspects involve methods. In some embodiments, the method includes mixing a liquid and a gas to form a two-phase solution; allowing the two-phase solution to flow over and / or through at least a portion of an electrode comprising a substrate including carbon-containing nonwoven fibers; and applying a voltage to the electrode such that at least a portion of the gas participates in a reaction to electrochemically generate a compound at the electrode. In some embodiments, the gas is passed through a liquid ring compressor prior to mixing the liquid and gas to form the two-phase solution. In some embodiments, a hydrophobic polymer and / or a catalyst layer is located on the substrate. The electrode comprises a substrate having a diameter greater than or equal to 100 cm⁻¹. 3 In a volumetric electrochemical system, the liquid flow rate of the two-phase solution is greater than or equal to 30 mL / min and / or the gas mass flow rate of the two-phase solution is greater than or equal to 0.2 slpm. In some embodiments, the electrode has a diameter greater than or equal to 1 cm. 2 The electrochemically active geometric area, and the liquid flow rate of the two-phase solution is greater than or equal to 30 mL / min and / or the gas mass flow rate of the two-phase solution is greater than or equal to 0.2 slpm. In some embodiments, the liquid flow rate and / or gas mass flow rate are based on per-cell metering.

[0011] In some embodiments, the liquid flow rate of the two-phase solution is greater than or equal to 200 mL / min and the gas mass flow rate of the two-phase solution is greater than or equal to 5 slpm. In some embodiments, the liquid flow rate and / or gas mass flow rate are based on a per-cell meter. In some embodiments, the compound is hydrogen peroxide. In some embodiments, the gas contains oxygen. In some embodiments, the liquid contains an alkaline hydroxide. In some embodiments, the liquid flows at a flow rate of at least 5 mL / min. In some embodiments, the gas flows at a mass flow rate of at least 0.5 slpm. In some embodiments, the liquid flow rate and / or gas mass flow rate are based on a per-cell meter. In some embodiments, the electrode is the cathode in the system. In some embodiments, the hydrophobic polymer is a first hydrophobic polymer and the catalyst layer comprises a second hydrophobic polymer and / or a carbon-containing active material, and the catalyst layer is formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer. In some embodiments, the surface area of ​​the active material is greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g. In some embodiments, the first and / or second hydrophobic polymer comprises PTFE particles. In some embodiments, the catalyst layer comprises less than or equal to 0.01% by weight of a metal.

[0012] In another aspect, a method is described. In some cases, the method includes flowing a solution over at least a portion of the surface area of ​​an electrode in a compartment; electrochemically generating a compound in the solution at the electrode; flowing the solution from the electrode through an outlet of the compartment; and recirculating at least a portion of the solution from the outlet of the compartment to an inlet of the compartment, such that the compound is present in the solution in an amount greater than or equal to 0.2% by weight. In some embodiments, the method further includes flowing the recirculated solution over and / or through at least a portion of the surface area of ​​the electrode. In some embodiments, the method further includes removing at least a portion of the solution containing the electrochemically generated compound. In some embodiments, the compound is hydrogen peroxide. In some embodiments, the electrode is part of a system comprising at least one gas manifold and at least one liquid manifold, wherein the at least one gas manifold and at least one liquid manifold supply only to a junction of gas and liquid inlets in a cathode or anode flow plate and / or flow box within the battery. In some embodiments, the electrode comprises a substrate comprising carbon-containing nonwoven fibers. In some embodiments, a hydrophobic polymer and / or catalyst layer is located on the substrate. In some embodiments, the electrode is the cathode in the system. In some embodiments, the hydrophobic polymer is a first hydrophobic polymer and the catalyst layer comprises a second hydrophobic polymer and / or a carbon-containing active material, and the catalyst layer is formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer. In some embodiments, the surface area of ​​the active material is greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g. In some embodiments, the first and / or second hydrophobic polymer comprises PTFE particles. In some embodiments, the catalyst layer comprises less than or equal to 0.01% by weight of a metal.

[0013] Other aspects still relate to methods. In some cases, a method for modifying an electrode includes: providing an electrode comprising a nonwoven substrate including carbon fibers; pretreating the electrode by applying a first solution comprising a liquid having a vapor pressure greater than or equal to 1 kPa and a first hydrophobic polymer to the electrode; and applying a second solution comprising a second hydrophobic polymer and / or a PTFE binder and a carbon-containing active material to the electrode. In some embodiments, the liquid in the first solution comprises an organic solvent. In some embodiments, the liquid in the first solution comprises a polar organic solvent. In some embodiments, the liquid in the first solution comprises an alcohol. In some embodiments, the liquid in the first solution comprises isopropanol. In some embodiments, the second solution comprises water. In some embodiments, the second solution comprises a surfactant. In some embodiments, the nonwoven substrate comprises a carbon felt. In some embodiments, the method further includes heating the electrode. In some embodiments, heating the electrode is performed in an atmosphere at a temperature greater than or equal to 380°C. In some embodiments, heating the electrode is performed in a non-oxidizing atmosphere. In some embodiments, the non-oxidizing atmosphere comprises less than or equal to 1% by weight of oxygen. In some embodiments, heating the electrode is performed in an atmosphere comprising N2 and / or Ar. In some implementations, the method further includes the step of repeating the pretreatment of the electrodes.

[0014] In some embodiments, the liquid in the first solution has a vapor pressure of less than or equal to 30 kPa. In some embodiments, the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the polytetrafluoroethylene (PTFE) particles of the first and / or second hydrophobic polymers are derived from PTFE powder and / or micronized powder.

[0015] Some aspects involve methods. In some cases, methods for electrochemically generating compounds include: purging the electrode stack by flowing a gas through it; flowing water through it; and applying a current with an absolute value less than or equal to 0.1 mA / cm². 2 Simultaneously, the electrolyte flow through the electrode stack is maintained for at least 1 minute; the absolute value of the applied current density is increased by at least 15 mA / cm² every 5 minutes. 2 And less than or equal to 125 mA / cm 2 Until the applied current density reaches at least 150 mA / cm². 2 The applied current is maintained at at least 150 mA / cm. 2 Simultaneously, compounds are electrochemically generated in the electrode stack and the electrode stack is heated to at least 35°C; and the absolute value of the applied current is increased to at least 300 mA / cm. 2In some embodiments, the water flowing through the electrode stack is deionized water. In some embodiments, the absolute value of the applied current density increases by 30 mA / cm² every 5 minutes. 2 Until the applied current density reaches at least 150 mA / cm². 2 In some embodiments, the compound is hydrogen peroxide. In some embodiments, heating the electrode stack includes Joule heating. In some embodiments, heating the electrode stack includes heating the electrolyte solution. In some embodiments, heating the electrolyte solution includes Joule heating. In some embodiments, heating the electrolyte solution includes using a resistance heating coil. In some embodiments, heating the electrolyte solution includes using a resistance heating coil. In some embodiments, heating the electrode stack includes using a heat exchanger. In some embodiments, the average temperature of the electrolyte solution as it flows into and / or through the electrode stack is at least 35°C. In some embodiments, the absolute value of the applied current density is less than or equal to 10 mA / cm². 2 The rate increases per minute.

[0016] In some embodiments, the electrochemical generation of the compound occurs at the electrodes in the electrode stack. In some embodiments, the electrode comprises a substrate including carbon-containing nonwoven fibers. In some embodiments, the electrode further comprises a first hydrophobic polymer formed on at least a portion of the substrate. In some embodiments, the electrode further comprises a catalytic layer on at least a portion of the substrate, the catalytic layer comprising a second hydrophobic polymer and / or an active material. In some embodiments, the first hydrophobic polymer and / or the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the active material comprises carbon. In some embodiments, the active material comprises less than or equal to 0.01% by weight of a metal. In some embodiments, the substrate comprises a carbon felt.

[0017] Some aspects involve methods. In some cases, methods for shutting down the electrode stack include: electrochemically generating compounds within the electrode stack; reducing the absolute value of the current applied to the electrode stack to less than or equal to 0.1 mA / cm². 2 When the absolute value of the applied current is less than or equal to 0.1 mA / cm 2Simultaneously, liquid is allowed to flow through the electrode stack for at least 1 minute; gas is then allowed to flow through the electrode stack to purge the liquid from it. In some embodiments, the liquid flow rate is greater than or equal to 0.2 mL / min and less than or equal to 5,000 mL / min, based on each individual cell meter. In some embodiments, the gas mass flow rate is greater than or equal to 0.2 slpm and less than or equal to 50 slpm, based on each individual cell meter. In some embodiments, the method further includes allowing water to flow through the electrode stack. In some embodiments, gas and water are simultaneously flowed through the electrode stack as a two-phase solution. In some embodiments, the water flowing through the electrode stack is deionized (DI) water. In some embodiments, the gas contains no CO2 or contains less than or equal to 5% CO2 by weight.

[0018] Some aspects involve methods. In some cases, methods for cleaning electrode stacks include: electrochemically generating compounds within the electrode stack; reducing the absolute value of the current applied to the electrode stack to less than or equal to 0.1 mA / cm². 2 The method removes precipitates from the electrode stack by flowing a solution containing a reducing agent and / or a chelating agent for less than or equal to 5 minutes; and by flowing water through the electrode stack for more than or equal to 30 minutes. In some embodiments, the water flowing through the electrode stack is deionized (DI) water. In some embodiments, the electrode stack is cleaned at least once a year. In some embodiments, the method further includes flowing gas through the electrode stack to dry it. In some embodiments, the gas is CO2-free or contains less than or equal to 5% by weight of CO2. In some embodiments, the gas and water (e.g., DI water) flow simultaneously through the electrode stack as a two-phase solution. In some embodiments, the gas is passed through a liquid ring compressor before flowing through the electrode stack. In some embodiments, the electrode stack, cleaned at least once a year, has a continuous operation life of more than or equal to 10,000 hours.

[0019] In some embodiments, the electrochemical generation of the compound occurs at the electrodes in the electrode stack. In some embodiments, the electrode comprises a substrate including carbon-containing nonwoven fibers. In some embodiments, the electrode further comprises a first hydrophobic polymer formed on at least a portion of the substrate. In some embodiments, the electrode further comprises a catalytic layer on at least a portion of the substrate, the catalytic layer comprising a second hydrophobic polymer and / or an active material. In some embodiments, the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles. In some embodiments, the active material comprises carbon. In some embodiments, the active material comprises less than or equal to 0.01% by weight of a metal. In some embodiments, the substrate comprises carbon felt. In some embodiments, the reducing agent comprises sodium bisulfite, sodium metabisulfite, and / or sodium sulfite. In some embodiments, the chelating agent comprises citric acid.

[0020] Some aspects involve methods. In some embodiments, a method for treating an electrochemical system includes: applying a solution at a rate greater than or equal to 20 mA / cm². 2 At least a portion of the electrodes in an electrochemical system operating at a current density of at least 100 hours are exposed to a treatment solution containing a reducing agent and / or a chelating agent. In some embodiments, when exposure is performed, the electrochemical system is already at a current density greater than or equal to 20 mA / cm². 2The method operates at a current density for at least 1,000 hours. In some embodiments, the method further includes restoring the current efficiency of the electrochemical cell to 70% of its efficiency prior to operation for at least 100 hours. In some embodiments, exposing at least a portion of the electrode to the treatment solution includes causing the solution to flow over and / or through at least a portion of the electrode. In some embodiments, the method further includes removing at least a portion of precipitates from the electrochemical system and / or removing hydrophilic sources from at least a portion of the electrode and / or removing contaminants from the electrochemical system. In some embodiments, the method further includes removing at least a portion of surface oxidation sources from at least a portion of the electrode. In some embodiments, the method further includes simultaneously flowing water and gas through the electrochemical system in the form of a two-phase solution for at least 1 minute. In some embodiments, the water flowing through the electrochemical system is deionized (DI) water. In some embodiments, the electrochemical system of the method is an electrolysis system, a fuel cell, and / or an air battery. In some embodiments, operation of the electrochemical system includes electrochemically generating a substance. In some embodiments, the substance is hydrogen peroxide. In some embodiments, operation of the electrochemical system includes electrochemically generating energy using the electrochemical system. In some embodiments, the electrode is a cathode. In some embodiments, the cathode comprises a nonwoven substrate containing carbon fibers. In some embodiments, the treatment solution comprises a reducing agent. In some embodiments, the reducing agent comprises a bisulfite anion. In some embodiments, the reducing agent comprises a bisulfite anion, ascorbic acid, oxalic acid, and / or a thiosulfate anion. In some embodiments, the reducing agent comprises sodium bisulfite. In some embodiments, the treatment solution comprises a chelating agent. In some embodiments, the chelating agent comprises NTA, TPP, citric acid, and / or EDTA. In some embodiments, the chelating agent comprises EDTA.

[0021] Other advantages and novel features of this disclosure will become apparent as they are considered in conjunction with the accompanying drawings in the following detailed description of various non-limiting embodiments of this disclosure. In the event of any conflicting and / or inconsistent disclosures between this specification and documents incorporated by reference, this specification shall prevail. Attached Figure Description

[0022] Non-limiting embodiments of this disclosure will be described by way of example with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale unless otherwise stated. In the drawings, each identical or substantially identical component is generally represented by a single number. For clarity, not every component is labeled in every drawing, nor are all components shown in every embodiment of this disclosure, provided that the illustrations are not essential for a person skilled in the art to understand this disclosure. In the drawings:

[0023] Figure 1 This is a schematic diagram of an electrochemical system based on some implementation schemes;

[0024] Figure 2A This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0025] Figure 2B This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0026] Figure 3 This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0027] Figure 4A This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0028] Figure 4B This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0029] Figure 4C This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0030] Figure 4D This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0031] Figure 4E This is a schematic diagram of an electrochemical system component according to some implementation schemes;

[0032] Figure 5A This is a schematic diagram of electrodes according to some implementation schemes;

[0033] Figure 5B -F is a schematic diagram related to the manufacture of electrodes according to some implementation schemes;

[0034] Figure 6 These are images of electrodes according to some implementation schemes;

[0035] Figure 7A These are images of electrodes according to some implementation schemes;

[0036] Figures 7B-7C yes Figure 7A The elemental diagram of the electrodes according to some embodiments is shown;

[0037] Figure 8 This is a flow recirculation method diagram based on some implementation schemes;

[0038] Figures 9A-9B These are images of preprocessed electrodes based on some implementation schemes;

[0039] Figure 10It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0040] Figure 11A-11B It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0041] Figure 12 It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0042] Figure 13 It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0043] Figure 14 It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0044] Figures 15A-15B It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0045] Figure 16 It is a graph showing the voltage of various electrodes over time according to some implementation schemes;

[0046] Figure 17 These are the IV curves of electrodes according to some implementation schemes; and

[0047] Figure 18 It is a graph showing the voltage and current efficiency of an electrochemical system based on some implementation schemes. Detailed Implementation

[0048] Some aspects of this disclosure generally relate to systems for the electrochemical generation of compounds (e.g., hydrogen peroxide) or other applications. In some cases, these systems may include an electrode comprising a substrate containing carbon-containing nonwoven fibers, hydrophobic particles (e.g., PTFE particles) on at least a portion of the substrate, and / or a catalytic layer comprising an active material (e.g., carbon particles) and / or hydrophobic particles on at least a portion of the substrate. In some embodiments, the system may generate a two-phase solution and / or allow the two-phase solution to flow on and / or through at least a portion of the electrode. Some systems using electrode structures and / or two-phase solutions may facilitate the formation of a three-phase interface, thereby potentially favoring the electrocatalytic generation of certain compounds at the three-phase interface. Other aspects relate to methods of manufacturing and / or using the system, etc.

[0049] Some electrocatalytic reactions involve gaseous and liquid reactants, and some are thought to occur at a three-phase interface formed between the gaseous reactant, liquid reactant, and solid electrode. Therefore, the formation (or lack thereof) of such a three-phase interface can limit the rate of electrocatalytic reactions in conventional systems. Furthermore, in some cases, the reaction rate of such reactions in conventional systems may be limited by the mass transport of reactants to the electrode surface, such as gaseous reactants, thus some reactants may be present at low concentrations on the electrode surface. The reaction rate of such reactions in conventional systems may also be limited by the mass transport of reactants away from the electrode surface. Therefore, some aspects of this disclosure relate to improved electrodes, systems, and methods for carrying out electrocatalytic reactions.

[0050] Some aspects of this disclosure relate to systems including electrodes. In some embodiments, the electrode may include a substrate having carbon-containing nonwoven fibers, hydrophobic particles (e.g., PTFE particles) on at least a portion of the surface of the substrate and / or the substrate fibers and / or penetrating through at least a portion of the thickness of the substrate (e.g., pretreatment), and a catalytic layer on at least a portion of the substrate comprising an active material containing carbon and / or hydrophobic particles. In some cases, the electrode preparation may form hydrophobic and hydrophilic islands on the electrode substrate. For example, applying hydrophobic particles (e.g., PTFE particles) to at least a portion of the nonwoven substrate (e.g., from a pretreatment step) can provide a hydrophobic electrode structure. Subsequently, applying a catalytic layer comprising an active material and / or hydrophobic particles can produce an electrode structure having relatively hydrophilic regions (e.g., the active material) and relatively hydrophobic regions (e.g., from pretreatment and / or hydrophobic particles in the catalytic layer). In some such cases, the presence of hydrophilic and hydrophobic regions can facilitate the formation of a three-phase interface by having various hydrophilic / hydrophobic interfaces at which liquid and gaseous reactants can advantageously interact with each other and / or with the electrode. Furthermore, the relatively open macroporous structure of nonwoven fibers allows for a relatively large and accessible surface area suitable for electrocatalytic reactions. The open macroporous structure also facilitates efficient mass transport with relatively minimal additional pressure drop.

[0051] In some cases, the system can generate a two-phase solution and / or allow the two-phase solution to flow over at least a portion of the electrode. The two-phase solution, as described more in other sections of this document, can increase the concentration and / or amount of gaseous reactants delivered to and / or present on the electrode surface, which can promote the formation of a three-phase interface on the electrode surface. For example, according to some embodiments, the electrode of the system can, as described above, have a substrate comprising a carbon-containing nonwoven fiber, hydrophobic particles (e.g., PTFE particles from a pretreatment step) on at least a portion of the substrate and / or the substrate fibers, and a catalytic layer comprising active material and / or hydrophobic particles on at least a portion of the substrate. In some such cases, as described elsewhere herein, the substrate may have been pretreated with hydrophobic particles prior to the addition of the catalytic layer. According to some such embodiments, the two-phase solution can flow over and / or through at least a portion of the electrode, which may promote a three-phase interface on the electrode surface. In the context of this disclosure, the inventors have recognized that using such electrodes and / or allowing two-phase solutions to flow can enhance the electrocatalytic performance of the system (e.g., improve the efficiency of generating hydrogen peroxide or other reactions), for example by promoting the formation of a three-phase interface.

[0052] Some aspects of this disclosure relate to methods. For example, some methods involve forming and using electrodes. In some cases, these methods involve forming a two-phase solution for use in an electrocatalytic system. Other aspects involve methods for allowing a two-phase solution to flow over an electrode structure, which may help facilitate electrocatalytic reactions, such as the electrocatalytic production of hydrogen peroxide or other compounds.

[0053] Figure 1 This is a schematic diagram of an exemplary peroxide generator system 1 according to some embodiments. System 1 comprises a stack S1 of electrochemical cells S2 (e.g., one or more pairs of anodes and / or cathodes). The electrode stack S1 includes an anode electrolyte inlet A7, an anode multiphase fluid outlet A8, a cathode electrolyte inlet C3, a cathode gas inlet O2, and a cathode multiphase fluid outlet C4. Although System 1 is described herein as a peroxide generator system, it should be understood that the system components, electrode structures, and system configurations can be used in certain situations to electrochemically generate other chemicals.

[0054] Anode electrolyte pump A5 is configured to pump anolyte from anolyte reservoir A4 to heat exchanger A6 via inlet HX3. Anode electrolyte flows from outlet HX4 of heat exchanger A6 to anolyte inlet A7. Cooling water is supplied to heat exchanger A6 via inlet HX1, and warm water is discharged from heat exchanger A6 via HX2. Anode electrolyte pumped into one or more anodes of battery S2, along with product gases (e.g., oxygen), can be discharged from anolyte outlet A8 to anolyte reservoir A4. Excess solution from anolyte reservoir A4 can be discharged via outlet A9. Fresh reactant solution (e.g., containing 50% by weight NaOH) can be transferred from tank A2 to anolyte reservoir A4 via pump A3.

[0055] The cathode electrolyte pump C2 is configured to pump the cathode electrolyte from the cathode electrolyte reservoir C5 to the cathode electrolyte inlet C3. Cathode electrolyte and gas pumped into one or more cathodes of the cell S2 in the stack S1 can be discharged from the cathode multiphase fluid outlet C4 to the cathode electrolyte reservoir C5 after the one or more cathodes electrogenerate a compound (e.g., H2O2). A solution containing the compound can be discharged from the cathode electrolyte reservoir C5 via the cathode electrolyte compound pump C6. Fresh reactant solution (e.g., water) can be delivered to the cathode electrolyte reservoir C5 via the reactant solution inlet C1. In some embodiments, fresh reactant solution (e.g., water) can be delivered to the cathode electrolyte inlet C3 via the cathode electrolyte pump C2.

[0056] The cathode electrolyte reservoir C5 and the anode electrolyte reservoir A4 have vents O3 and O4, respectively. Excess reactant gas (e.g., oxygen) from the headspace of the cathode electrolyte reservoir C5 and / or product gas (e.g., oxygen) from the headspace of the anode electrolyte reservoir A4 can flow to the collector O8 through vents O3 and O4. In some embodiments, the product gas and / or excess reactant gas may have separate circulation loops or external vents from the anode and / or cathode. In some embodiments, no gas may be generated at the cathode and / or anode of each electrochemical cell in the electrochemical system. The gas is pumped to the reactant reservoir O7 via a liquid ring compressor O5. The gas flows from the reactant reservoir O7 to one or more cathodes of the cell S2 through the cathode gas inlet O2. In the exemplary embodiment shown, the gas flowing into the cell S2 and the cathode electrolyte flowing into the cell S2 from the cathode electrolyte reservoir C5 can form a two-phase solution. In some embodiments, the gas flowing into battery S2 and the anolyte flowing into battery S2 from anolyte reservoir A4 can form a two-phase solution. According to some embodiments, the two-phase solution can be formed within each battery S2 of the stack S1 and then flow through one or more cathodes and / or one or more anodes of system 1. Additional reactant gas can be added to reactant reservoir O7 via inlet O1. Reactant reservoir O7 contains gas and water. Water flows from reservoir O7 to heat exchanger O6 via inlet HX7 and returns to reservoir O7 via outlet HX8. Cooling water is supplied to heat exchanger O6 via inlet HX5, and warm water is discharged from heat exchanger O6 via HX6. After flowing through liquid ring compressor O5, the gas in reactant reservoir O7 can have a relatively high relative humidity (e.g., at least 50%, at least 75%, up to 100%, or other values ​​as described elsewhere herein).

[0057] Typically, reactant streams are introduced into system 1 and power is supplied to the system, causing an electrochemical reaction to occur within the electrolysis unit S1, such as the generation of hydrogen peroxide at the cathode. After the reactant solution flows through the electrode stack S1, solutions containing electrochemically generated compounds from one or more anodes and / or one or more cathodes flow to corresponding storage tanks A4 and C5. In some embodiments, the electrochemically generated compounds from one or more cathodes may flow to the cathode electrolyte storage tank C5, a portion of which may be pumped out and / or recycled back into stack S1 by pump C6. The pumped-out solution may, in some cases, be prepared for commercial use, sale, and / or use in other applications or systems.

[0058] Figure 2ASystem 80 is shown, comprising an electrode stack 40 having an electrochemical cell 42, the electrochemical cell 42 comprising an anode assembly 43 and a cathode assembly 44, wherein at least a portion of the anode assembly and cathode assembly are separated by a membrane. The electrode stack of this system may contain a variety of suitable numbers of electrochemical cells containing anode and cathode assemblies. For example, the electrode stack may contain at least 1, at least 2, at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 60 and / or no more than 70, no more than 80, no more than 90, or no more than 100 electrochemical cells. The anode assembly comprises anode electrode material and a flow plate or flow frame, the flow plate or flow frame may contain channels and / or pathways for conveying reactants from an internal and / or external manifold to the anode electrode. The cathode assembly comprises cathode electrode material and a flow plate and / or flow frame, the flow plate and / or flow frame may contain channels and / or pathways for conveying reactants from an internal and / or external manifold to the cathode electrode. The stack 40 of cells 42 can be compressed using plates 45 and 46, while current collectors 9 and 10 may be present to apply voltage and / or current to the stack 40. Anode inlets 47 and 48, and cathode inlets 49 and 50, may be configured to deliver electrolyte solution and / or reactant gas to each electrochemical cell 42 in the stack 40 (e.g., anode inlets and outlets configured with an anode, cathode inlets and outlets configured with a cathode). In some embodiments, each inlet may be configured to deliver a two-phase solution to each electrochemical cell. In some embodiments, the gas inlet port and the liquid inlet port intersect within a flow plate or flow frame in a cathode or anode assembly upstream of at least one electrode within the electrochemical cell to generate a two-phase solution flowing through that at least one electrode. For example, two cathode inlets 49 are shown, one for delivering gas and one for delivering liquid, wherein the gas and liquid will mix within the cathode assembly 44 to form a two-phase solution, which is then delivered to each cathode electrode in the cathode assembly 44 within the stack 40. In some cases, each cathode and / or anode flow plate and / or flow frame within the electrochemical cell in the electrode stack includes at least one such junction where a two-phase solution can be generated to flow through the cathode and / or anode electrodes of the electrochemical cell. According to some embodiments, such as Figure 2A In the illustrated embodiment, only the cathode cell is fluidly connected to such a junction where a two-phase solution can be generated. An example embodiment of such an inlet is shown in... Figure 3 -4 in.

[0059] Figure 2BThis is a schematic diagram showing a cross-sectional view of the electrochemical cell 500. The diagram shows electrical contacts 510 and 530 connected to the cathode 514 and anode 534, respectively. As indicated by the arrows, the solution flows from inlet 520 through the cathode substrate 512 of the electrochemical cell 500 to outlet 522. The solution flows from anode inlet 540 through and / or through anode substrate 532 to anode outlet 542. Furthermore, the anode block and cathode block are separated by a diaphragm 550, which allows ion flow to pass between them.

[0060] Figure 3 This is a schematic diagram illustrating the use of a two-phase solution in the cathode block of an electrochemical cell. Here, the two-phase solution 600 flows through the inlet manifold 610, through the cathode substrate 512, and out of the outlet manifold 620. Note that the concentration of the gaseous substance decreases after passing through the cathode substrate 512 because the gaseous substance participates in the target reaction (e.g., hydrogen peroxide generation). Figure 4A Another embodiment of the cathode block is shown. In this case, gas 702 and liquid 704 are injected separately to form a two-phase solution 600 at the intersection upstream of the cathode 510. In some cases, the two-phase solution can be distributed on the cathode via an inlet manifold (e.g., a branch and / or parallel inlet array) to introduce the two-phase solution substantially uniformly into the cathode. In some cases, the two-phase solution can be formed and injected into portions of the electrode at multiple intersections supplied by different manifolds. According to some embodiments, a similar structure is also feasible in the anode.

[0061] According to some embodiments, each gas and / or liquid manifold within the stack supplies only one intersection of the gas and liquid inlets in the cathode or anode flow plate and / or flow box within the battery. In some embodiments, each intersection of the gas and liquid inlets in the cathode or anode flow plate and / or flow box within the battery is supplied only by a single gas and / or liquid manifold within the stack. For example, see... Figure 4B-4C . Figure 4B An exemplary cathode assembly 470 is shown, comprising a cathode substrate 480 having a liquid manifold 472 and a gas manifold 474. The liquid manifold 472 and the gas manifold 474 intersect at a single point 476 to form a two-phase flow. Figure 4C A similar alternative embodiment is shown, in which multiple pairs of liquid manifolds 474 and gas manifolds 472 exist, but each pair intersects only at a single point 476. Such an embodiment can provide advantages related to generating a relatively homogeneous two-phase solution to flow through the cathode substrate 480. (Figure) Figure 4D-4E Embodiments of exemplary cathode assemblies 470 are also shown, including a cathode substrate 480 having a liquid manifold 472 and a gas manifold 474. In these cases, the liquid and gas manifolds 472 and 474 supply multiple junctions 476, and the resulting two-phase solution may be less... Figure 4B-4CThe components shown are as uniform.

[0062] Figure 5A Exemplary electrode structures 200 are shown that can be used in some of the systems described herein. Electrode 200 may comprise a substrate 220 coated with hydrophobic polymer 210 particles. A catalytic layer 230 may subsequently be formed on the hydrophobic polymer 210 particles and the substrate 220. In some embodiments, when used as an electrode (e.g., a cathode) in a system, the electrode structure can facilitate the electrocatalytic generation of a desired compound (e.g., hydrogen peroxide). Although Figure 5A The substrate is shown as a planar substrate, but it should be understood that this is a simplified schematic diagram of an enlarged view of the substrate. For example, in some cases, Figure 5A A single surface of a single fiber in a nonwoven substrate containing fibers can be shown.

[0063] While many embodiments disclosed herein relate to systems and methods associated with the electrocatalytic generation of H2O2, it should be understood that other electrocatalytic reactions are also considered. A variety of other compounds can be electrocatalyzed. In some cases, using the systems and / or methods disclosed herein may be advantageous for electrocatalytic reactions due to the formation of a three-phase interface or the introduction of a two-phase solution. Exemplary electrocatalytic processes of interest include, but are not limited to, oxygen reduction (e.g., formation of water or OH-). - The four-electron pathway of ions, and / or the formation of H₂O₂ and possibly OH⁻. - The two-electron pathway of ions; both of these cases depend on pH), nitrogen fixation, chlor-alkali processes, and CO2 reduction.

[0064] In some cases, these electrodes in the systems disclosed herein are believed to improve the formation of three-phase interfaces, which may increase the Faraday efficiency at the electrodes and / or reduce activation and / or concentration polarization during certain electrochemical reactions. In some embodiments, the electrode structures in the system may preferentially catalyze certain electrocatalytic reactions via certain pathways (e.g., the two-electron reduction of oxygen to hydrogen peroxide versus the four-electron pathway of oxygen to water). In some cases, the electrode structures described herein can be used as cathodes in the system. For example, in some embodiments, each cathode in an electrode stack may contain the electrode structures described herein.

[0065] According to some implementation schemes, the electrode structure may include a substrate. For example, consider again... Figure 5A , Figure 5AAn illustrative schematic diagram of the substrate 220 of electrode 200 is shown. In some cases, the substrate comprises nonwoven fibers. In some embodiments, the substrate comprises carbon-containing nonwoven fibers. In some embodiments, the substrate comprises elemental carbon-containing nonwoven fibers. In some embodiments, the substrate comprises graphitized carbon-containing nonwoven fibers. In some embodiments, the substrate comprises nonwoven carbon fibers. According to some embodiments, the substrate is composed of nonwoven carbon fibers. In some cases, the substrate comprises felt, such as carbon felt. In some cases, the fibers may be entangled not by weaving but by needle punching, matting, cohesion, pressing, or other common methods (e.g., wet web laying and / or electrospinning and / or suction deposition onto a porous substrate). Other methods are also possible.

[0066] For example, although Figure 5A The substrate is a planar substrate, but Figure 6 This is an SEM image of an electrode 300 containing a coated substrate. The substrate contains nonwoven fibers 310.

[0067] Advantageously, the substrate comprising nonwoven fibers can be relatively porous and / or can have a relatively thick three-dimensional structure. In some cases, each of these factors can promote gas and liquid mixing and / or not promote phase separation when a two-phase solution flows on and / or through a portion of the substrate, compared to other woven or paper substrates. In some embodiments, the combination of an open-pore structure with a high surface area catalyst can promote an accessible and relatively large surface area on which electrocatalytic reactions can occur. In some embodiments, the relatively thick three-dimensional structure of the nonwoven fibers of the substrate can contain a relatively large active region when used for electrocatalytic applications. According to some embodiments, using an electrode comprising a substrate containing nonwoven fibers with large open pores can result in an electrode structure that does not wet at a significant rate (e.g., can maintain a certain degree of hydrophobicity), which can extend the electrode lifetime depending on the application, for example, compared to systems using electrodes comprising carbon cloth, paper, or other woven materials with relatively small pores (which may be more easily submerged). Furthermore, according to some embodiments, the nonwoven properties of certain substrates can advantageously provide relatively open volumes within the substrate through which solutions can flow. As described in more detail below, in some cases, the solution (e.g., a two-phase solution) can flow through an open volume of the substrate. In some embodiments, the open volume can increase the surface area on which the electrocatalytic reaction can take place.

[0068] Other embodiments include substrates comprising woven fabrics and / or paper. For example, according to some embodiments, carbon-containing woven fabrics and / or carbon-containing paper can be used as substrates.

[0069] According to some embodiments, a variety of fibers can be used in the nonwoven substrate. In some cases, the fibers may contain carbon. In some cases, the fibers may contain graphitized carbon. In some cases, the fibers may contain amorphous carbon. In some embodiments, the precursors for carbon fibers may be polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and / or polyacrylonitrile (PAN). Other precursors are also possible.

[0070] According to some implementations, the electrode substrate can be relatively thick, for example, compared to common substrate materials such as woven fabric (e.g., cloth containing woven fibers) or paper. In some cases, the relatively high thickness of the substrate containing nonwoven fibers can result in relatively easy access and / or a high surface area on which electrocatalytic reactions can occur.

[0071] According to some embodiments, the substrate of the system's electrodes can have any of a variety of suitable thicknesses. In some embodiments, the average shortest dimension of the substrate is greater than or equal to 100 micrometers, greater than or equal to 500 micrometers, greater than or equal to 750 micrometers, greater than or equal to 1 millimeter, or greater than or equal to 3 millimeters. In some cases, the average shortest dimension of the substrate is less than or equal to 5 millimeters, less than or equal to 3 millimeters, less than or equal to 1 millimeter, less than or equal to 750 micrometers, or less than or equal to 500 micrometers. Combinations of the above ranges are possible (e.g., greater than or equal to 500 micrometers and less than or equal to 5 millimeters). Other ranges are also possible. In some such embodiments, the substrate is a nonwoven substrate. In some such embodiments, the average shortest dimension of the substrate corresponds to the thickness of the substrate.

[0072] According to some embodiments, the electrode substrate has any of the aforementioned thicknesses before being integrated into the electrochemical system as described herein, which may be the uncompressed thickness of the substrate. In some embodiments, the electrode substrate is compressed upon integration into the electrochemical system, wherein the substrate has a compressed thickness upon integration. In some embodiments, the ratio of the uncompressed thickness of the electrode substrate to the compressed thickness of the electrode substrate is greater than or equal to 1.05, greater than or equal to 1.1, greater than or equal to 1.2, greater than or equal to 1.25, greater than or equal to 1.3, greater than or equal to 1.4, greater than or equal to 1.5, greater than or equal to 1.6, greater than or equal to 1.7, greater than or equal to 1.8, greater than or equal to 1.9, or greater. In some embodiments, the ratio of the uncompressed thickness of the electrode substrate to the compressed thickness of the electrode substrate is less than or equal to 2.0, less than or equal to 1.9, less than or equal to 1.8, less than or equal to 1.7, less than or equal to 1.6, less than or equal to 1.5, less than or equal to 1.4, less than or equal to 1.3, less than or equal to 1.25, less than or equal to 1.2, or less than or equal to 1.1, or smaller. Combinations of the above ranges are possible (e.g., greater than or equal to 1.05 and less than or equal to 2.0, or greater than or equal to 1.05 and less than or equal to 1.5). Other ranges are also possible.

[0073] According to some implementation schemes, the substrate containing nonwoven fibers may have a thickness greater than or equal to 0.01 m. 2 / g, greater than or equal to 0.05 m 2 / g, greater than or equal to 0.1 m 2 / g, greater than or equal to 0.5 m 2 / g or greater than or equal to 1 m 2 / g surface area. In some cases, the substrate containing nonwoven fibers may have a surface area of ​​less than or equal to 2 m². 2 / g, less than or equal to 1 m 2 / g, less than or equal to 0.5 m 2 / g, less than or equal to 0.1 m 2 / g or less than or equal to 0.05 m 2 / g surface area. Combinations of the above ranges are possible. Other ranges are also possible. In some implementations, the surface area is measured using Brunauer-Emmett-Teller (BET) surface area analysis.

[0074] According to some embodiments, the substrate may have any of a variety of porosities. In some cases, the porosity can be measured by mercury porosimetry. According to some embodiments, the substrate may have a porosity greater than or equal to 0.1, greater than or equal to 0.2, greater than or equal to 0.3, greater than or equal to 0.4, greater than or equal to 0.5, greater than or equal to 0.6, greater than or equal to 0.7, greater than or equal to 0.8, greater than or equal to 0.85, greater than or equal to 0.9, greater than or equal to 0.94, or greater than or equal to 0.95. In some cases, the substrate may have a porosity less than or equal to 0.99, less than or equal to 0.95, less than or equal to 0.94, less than or equal to 0.9, less than or equal to 0.85, less than or equal to 0.8, less than or equal to 0.7, less than or equal to 0.6, less than or equal to 0.5, less than or equal to 0.4, less than or equal to 0.3, or less than or equal to 0.2. Combinations of the above ranges are possible (e.g., greater than or equal to 0.2 and less than or equal to 0.5). Other ranges are also possible.

[0075] In some embodiments, the substrate may have an open macroporous structure. In some embodiments, the average minimum cross-sectional size of the pores in the substrate is less than or equal to 200 micrometers, less than or equal to 100 micrometers, less than or equal to 50 micrometers, or less than or equal to 10 micrometers. In some embodiments, the average minimum cross-sectional size of the pores in the substrate is greater than or equal to 1 micrometer, greater than or equal to 10 micrometers, greater than or equal to 50 micrometers, or greater than or equal to 100 micrometers. Combinations of the above ranges are possible. Other ranges are also possible.

[0076] The first hydrophobic polymer can be deposited on at least a portion of the substrate (e.g., as a pretreatment step). In some cases, the first hydrophobic polymer can penetrate into the void spaces of the substrate and / or form a coating on at least a portion of some fibers of the substrate. In some cases, the first hydrophobic polymer can penetrate and cover at least a portion of the substrate depth. In some cases, the coating may penetrate and / or coat the entire depth of the substrate (e.g., particles of the first hydrophobic polymer may be present on at least some fibers at each depth of the substrate). The hydrophobic polymer can comprise any of a variety of hydrophobic polymers. In some cases, the hydrophobic polymer may comprise a fluorinated polymer. Exemplary hydrophobic polymers include, but are not limited to, ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), perfluoroalkoxyalkane (PFA), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE). In some embodiments, the hydrophobic polymer comprises PTFE.

[0077] The first hydrophobic polymer may be applied as a pretreatment. It should be understood that "pretreatment" is a term used for convenience and is not intended to necessarily imply any order in which the first polymer must be applied to the substrate. In some cases, the hydrophobic polymer may form a coating on at least a portion of the substrate surface. In some embodiments, the hydrophobic polymer pretreatment may be present on the electrode in the form of hydrophobic polymer particles. According to some embodiments, the hydrophobic polymer particles may form a partial and / or conformal coating on the substrate surface.

[0078] In some cases, hydrophobic polymers can be deposited as particulate hydrophobic materials on a substrate. For example, see [link to relevant documentation]. Figure 5A It shows a substrate 220 for electrode 200, wherein hydrophobic particles 210 can form a partial layer on substrate 220. See also Figure 5B It shows a substrate 580, in which hydrophobic particles 586 can penetrate to the entire depth of the substrate 580.

[0079] In some cases, particles of the first hydrophobic polymer can penetrate at least 5%, at least 10%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the substrate thickness. In some cases, the polymer penetrates to the entire depth of the substrate thickness, not exceeding 90%, not exceeding 80%, not exceeding 70%, not exceeding 60%, not exceeding 50%, not exceeding 40%, not exceeding 30%, not exceeding 25%, not exceeding 20%, or not exceeding 10%.

[0080] According to some embodiments, any of various sizes of hydrophobic particles (e.g., PTFE particles) can be used during the pretreatment of the electrode substrate. In some cases, hydrophobic particles can be used such that they do not aggregate and maintain a relatively large hydrophobic surface area. In some embodiments, powders and / or microparticles of hydrophobic polymers (e.g., PTFE powder) can be suspended in a solvent and used such that they do not aggregate and maintain a relatively large hydrophobic surface area. Conventional PTFE dispersions utilize surfactants to stabilize PTFE particles in the solvent to prevent particle aggregation. In some such cases, such dispersions may not achieve the uniform distribution of PTFE required for deep penetration into the substrate, for example, due to the presence of surfactants, as surfactants allow PTFE to move during drying. Therefore, in some embodiments, and as described in more detail elsewhere herein, PTFE can be applied to the substrate in the absence of surfactants.

[0081] According to some implementations, the average maximum cross-sectional size of the hydrophobic particles can be greater than or equal to 100 nanometers, greater than or equal to 500 nanometers, greater than or equal to 1 micrometer, greater than or equal to 3 micrometers, greater than or equal to 5 micrometers, greater than or equal to 10 micrometers, greater than or equal to 25 micrometers, or greater than or equal to 50 micrometers. In some cases, the average maximum cross-sectional size of the hydrophobic particles can be less than or equal to 100 micrometers, less than or equal to 50 micrometers, less than or equal to 25 micrometers, less than or equal to 10 micrometers, less than or equal to 5 micrometers, less than or equal to 3 micrometers, less than or equal to 1 micrometer, or less than or equal to 500 nanometers. Combinations of the above ranges are possible (e.g., greater than or equal to 1 micrometer and less than or equal to 10 micrometers). Other ranges are also possible.

[0082] In some cases, hydrophobic particles present on the electrode substrate surface can be relatively stable and / or may not significantly aggregate. According to some embodiments, the average maximum cross-sectional size of the hydrophobic particles may not change and / or may change by a relatively small amount after deposition on the electrode and / or surface treatment of the electrode, as described in more detail elsewhere herein. In some embodiments, the average maximum cross-sectional size of the hydrophobic particles may change by no more than 50%, no more than 25%, no more than 10%, or no more than 5% before the electrode containing these particles is used, for example, for electrocatalysis. This may be because the hydrophobic particles remain in suspension in solution and do not aggregate.

[0083] In some cases, the electrode substrate may be pretreated with hydrophobic particles as described in more detail elsewhere in this document. The hydrophobic particles on the electrode may, in some cases, form a partial layer on the electrode. According to some embodiments, a higher number density of particles on the substrate surface may result in a more complete layer, e.g., up to a conformal layer. In some embodiments, where the substrate is a porous three-dimensional substrate with void spaces throughout its volume, the particles may be distributed throughout the entire volume of the substrate. In some such embodiments, the particles may be substantially uniformly distributed throughout the entire volume of the substrate.

[0084] According to some embodiments, using methods described elsewhere herein, hydrophobic particles (e.g., PTFE particles) used during pretreatment can be located on at least a portion of the surface area of ​​the substrate. In some cases, when the substrate contains nonwoven fibers (e.g., carbon felt), the hydrophobic particles can cover at least a portion of the substrate surface, including within the internal volume of the substrate (e.g., within the void spaces of the substrate). In some cases, the hydrophobic particles can be deposited relatively uniformly on the substrate surface; for example, the particles can be uniformly distributed on the surface of the substrate in contact with the atmosphere and / or solution, and the substrate can be immersed in the atmosphere and / or solution. In some such cases, as described elsewhere herein, the particles may not significantly aggregate and / or may only cover a portion of the surface.

[0085] In some embodiments, the concentration of hydrophobic particles (e.g., PTFE particles) used in the solution deposited on the electrode substrate can be varied. In some cases, the concentration of hydrophobic particles can be selected such that these particles form a layer covering more than or equal to 1%, 10%, 20%, 30%, 40%, or 50% of the substrate surface area. In some embodiments, the hydrophobic particles may form a layer covering less than or equal to 60%, 50%, 40%, 30%, 20%, or 10% of the substrate surface area. Combinations of the above ranges are possible. Other ranges are also possible.

[0086] According to some embodiments, hydrophobic particles can be relatively uniformly distributed on at least a portion of the surface area of ​​the electrode substrate (e.g., a nonwoven substrate), such as at least 5%, at least 25%, at least 50%, at least 75%, or more of the substrate surface area. In some cases, the hydrophobic particles can be relatively uniformly distributed across the entire substrate. To achieve a relatively uniform distribution on the surface, the particle number density distributed on the electrode surface area can vary by no more than 50%, no more than 25%, no more than 10%, or no more than 5% relative to the average particle number, wherein the average number can be determined by analyzing SEM images of example electrode regions.

[0087] In some embodiments, the hydrophobic polymer may be present in the solution applied to the electrode in amounts greater than or equal to 0.01 wt%, greater than or equal to 0.1 wt%, greater than or equal to 1 wt%, greater than or equal to 2 wt%, greater than or equal to 5 wt%, greater than or equal to 10 wt%, greater than or equal to 15 wt%, greater than or equal to 20 wt%, greater than or equal to 30 wt%, or greater than or equal to 40 wt%. In some cases, the hydrophobic polymer may be present in the solution applied to the electrode in amounts less than or equal to 50 wt%, less than or equal to 40 wt%, less than or equal to 30 wt%, less than or equal to 20 wt%, less than or equal to 15 wt%, less than or equal to 10 wt%, less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, or less than or equal to 0.1 wt%. Combinations of the above ranges are possible. Other ranges are also possible.

[0088] According to some embodiments, a hydrophobic polymer on the substrate can impart a degree of hydrophobicity to the electrode substrate. According to some embodiments, after the hydrophobic polymer is applied to the substrate (e.g., through electrode pretreatment and / or preparation), the hydrophobicity of the electrode substrate can be measured by any of a variety of methods. In some cases, the hydrophobicity of the substrate can be determined by measuring the water contact angle on the substrate. In some embodiments, a planar non-porous material can be prepared in other similar ways, and then the water contact angle of the substrate can be measured. According to some embodiments, the water contact angle of the substrate before any operation is performed in the cell is greater than or equal to 90 degrees, greater than or equal to 100 degrees, greater than or equal to 110 degrees, or greater than or equal to 120 degrees. In some embodiments, the water contact angle of the substrate before any operation is performed in the cell is less than or equal to 130 degrees, less than or equal to 120 degrees, less than or equal to 110 degrees, or less than or equal to 100 degrees. Combinations of the above ranges are possible. Other ranges are also possible.

[0089] In some embodiments, the electrode may further comprise a catalytic layer deposited on a substrate. In some cases, a hydrophobic polymer pretreatment may be present on at least a portion of the substrate prior to depositing the catalytic layer on the substrate. For example, refer again... Figure 5A The catalyst layer 230 can be formed on the substrate 220 and on particles of the hydrophobic polymer 210 present on at least a portion of the substrate. Although Figure 5A Not shown, but in some cases, the catalyst layer may contact the substrate on at least a portion of the substrate (e.g., a non-intervening hydrophobic polymer). In other embodiments, the catalyst layer may not directly contact the substrate, such as... Figure 5A As shown. In some cases, this may be due to the presence of an intermediate layer of hydrophobic polymer particles on the substrate, wherein the catalyst layer can be formed on the substrate but in direct contact with the hydrophobic polymer. In some embodiments, the catalyst layer can be in direct contact with the substrate and / or in direct contact with the hydrophobic polymer on the substrate.

[0090] In some embodiments, the catalyst layer comprises an active material and / or a binder and / or additional hydrophobic particles. According to some such embodiments, the binder may be a second hydrophobic polymer, wherein the composition of the second hydrophobic polymer may be the same as described above for the first hydrophobic polymer. For example, the second hydrophobic polymer may be or comprise PTFE particles. In some embodiments, the binder may be in the form of a commercially available PTFE dispersion or emulsion. In some embodiments, the additional hydrophobic particles may be different forms of PTFE particles, such as PTFE powder or microparticles. In some embodiments, the additional hydrophobic particles may be a combination of a binder and powder or microparticles. According to some embodiments, the active material may be carbon or contain carbon. In some embodiments, the active material may comprise carbon nanoparticles, carbon microparticles, carbon flakes, carbon allotropes (e.g., graphite, graphene, amorphous carbon), etc. In some embodiments, the active material may promote catalytic reactions, such as oxygen reduction reactions, CO2 reduction reactions, etc., at relatively low voltages relative to the voltages required in the absence of the active material.

[0091] In some embodiments, the size of the active material can be any of a variety of suitable sizes. In some cases, the average maximum size of the active material particles is at least 10 nm, at least 100 nm, at least 1 micrometer, or at least 10 micrometers. In some embodiments, the average maximum size of the active material particles is no more than 100 micrometers, no more than 10 micrometers, no more than 1 micrometer, or no more than 100 nanometers. Combinations of the above ranges are possible. Other ranges are also possible.

[0092] In some embodiments, the active material (e.g., carbon) can have a relatively high surface area. In some cases, a relatively high surface area can promote the formation of many and / or various types of interfaces, such as at and / or near the interfaces between the solution (e.g., the two-phase solution described elsewhere herein), the active material, and / or hydrophobic polymers present in the catalyst layer and / or present on the substrate, and at tri-phase interfaces. In some cases, the surface area of ​​the active material can be greater than or equal to 0.5 m². 2 / g, greater than or equal to 1 m 2 / g, greater than or equal to 5 m 2 / g, greater than or equal to 10 m 2 / g, greater than or equal to 50 m 2 / g, greater than or equal to 100 m 2 / g, greater than or equal to 500 m 2 / g, greater than or equal to 1,000 m 2 / g, greater than or equal to 2,000 m 2 / g, greater than or equal to 3,000 m 2 / g or greater than or equal to 4,000 m 2 / g. In some embodiments, the surface area of ​​the active material may be less than or equal to 5,000 m². 2 / g, less than or equal to 4,000 m 2 / g, less than or equal to 3,000 m 2 / g, less than or equal to 2,000m 2 / g, less than or equal to 1,000 m 2 / g, less than or equal to 500 m 2 / g, less than or equal to 100 m 2 / g, less than or equal to 50m 2 / g, less than or equal to 10 m 2 / g, less than or equal to 5 m 2 / g or less than or equal to 1 m 2 / g. Combinations of the above ranges are possible. Other ranges are also possible. In some implementations, the surface area is measured using Brunauer-Emmett-Teller (BET) surface area analysis.

[0093] In some embodiments, the active material may be present in the solution applied to the electrode in an amount greater than or equal to 0.01 wt%, greater than or equal to 0.1 wt%, greater than or equal to 1 wt%, greater than or equal to 2 wt%, greater than or equal to 5 wt%, greater than or equal to 10 wt%, greater than or equal to 15 wt%, greater than or equal to 20 wt%, greater than or equal to 30 wt%, or greater than or equal to 40 wt%. In some cases, the active material may be present in the solution applied to the electrode in an amount less than or equal to 50 wt%, less than or equal to 40 wt%, less than or equal to 30 wt%, less than or equal to 20 wt%, less than or equal to 15 wt%, less than or equal to 10 wt%, less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, or less than or equal to 0.1 wt%. Combinations of the above ranges are possible. Other ranges are also possible.

[0094] In some embodiments, the active material (e.g., carbon) can be added to the catalyst layer in any of a variety of suitable amounts. In some embodiments, the amount of active material added is greater than or equal to 0.1 mg / cm³. 2 ≥0.25 mg / cm 2 ≥0.5 mg / cm 2 ≥1 mg / cm 2 ≥1.5 mg / cm 2 ≥2 mg / cm 2 ≥2.5 mg / cm2 ≥3 mg / cm 2 ≥3.5 mg / cm 2 ≥4 mg / cm 2 or greater than or equal to 4.5 mg / cm 2 The substrate geometry exists. In some embodiments, the active material is added such that it is less than or equal to 5 mg / cm². 2 Less than or equal to 4.5 mg / cm 2 Less than or equal to 4 mg / cm 2 Less than or equal to 3.5 mg / cm 2 Less than or equal to 3 mg / cm 2 Less than or equal to 2.5 mg / cm 2 Less than or equal to 2 mg / cm 2 Less than or equal to 1.5 mg / cm 2 Less than or equal to 1 mg / cm 2 or less than or equal to 0.5 mg / cm 2 The geometric area of ​​the substrate exists. Combinations of the above ranges are possible. Other ranges are also possible.

[0095] In some embodiments, the catalyst layer does not contain a significant amount of metal (e.g., an immeasurable amount, such as that measured by EDS). This can be advantageous, according to some embodiments, because when metal is present, it may decompose the electrochemically generated compound (e.g., hydrogen peroxide) and / or the metal may be expensive. In some embodiments, the metal may not provide any advantage to the efficiency of the reaction, for example, when the electrochemically generated compound is hydrogen peroxide and the reaction occurs in an alkaline solution.

[0096] In other embodiments, the catalyst layer comprises an active material containing a metal. For example, the amount of metal present in the active material may be at least 0.0001 wt%, at least 0.001 wt%, at least 0.01 wt%, at least 0.1 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt%, at least 30 wt%, at least 40 wt%, or at least 50 wt%. In some embodiments, the metal may be present in the active material in amounts less than or equal to 60 wt%, less than or equal to 50 wt%, less than or equal to 40 wt%, less than or equal to 30 wt%, less than or equal to 20 wt%, less than or equal to 10 wt%, less than or equal to 5 wt%, less than or equal to 1 wt%, less than or equal to 0.1 wt%, less than or equal to 0.01 wt%, or less than or equal to 0.001 wt%. In some embodiments, the metal may be present only in trace amounts. According to some implementation schemes, the metal of the active material may include, but is not limited to, iron, nickel, cobalt, gold, platinum, iridium, palladium, silver, rhodium, copper, zinc, their oxides, their salts, and / or their organometallic complexes such as porphyrins. Other metals and metal-containing compounds are also possible.

[0097] In some embodiments, such as for electrocatalytic reactions or other reactions including 2-electron oxygen reduction, CO2 reduction, nitrogen fixation, and / or 4-electron oxygen reduction, the catalyst layer may comprise an active material containing a metal. For example, in some embodiments, the active material may further comprise metal nanoparticles. The average maximum cross-sectional size of the nanoparticles in the active material may, in some cases, not exceed 100 nm, 50 nm, 20 nm, or 10 nm. In some embodiments, the average maximum cross-sectional size of the nanoparticles in the active material may be at least 5 nm, at least 10 nm, at least 20 nm, or at least 50 nm. Combinations of the above ranges are possible. Other ranges are also possible. Furthermore, other forms of metal may be present in the catalyst layer, such as dopants, single atoms, and particles.

[0098] Once the catalyst layer is deposited, in some cases, hydrophobic island-like regions may form on at least a portion of the electrode surface, some of which may be at least partially surrounded by a hydrophilic surface. In some embodiments, the hydrophobic islands on the electrode surface can be determined using images collected by SEM and elemental analysis performed by energy-dispersive X-ray spectroscopy (EDS). For example, refer again... Figure 6 SEM images show the electrode 300 containing a nonwoven fiber 310 substrate. Aggregates of the catalyst layer 320 can be observed on a portion of the substrate surface.

[0099] Figure 7A This is another image acquired using SEM, with a magnification higher than [previous value]. Figure 6 , Figures 7B-7C It is a distribution map of the corresponding elements collected using EDS. Figure 7A The image shown is an exemplary electrode structure 400, which includes active material 410 and PTFE particles 420. Figure 7B Showing from Figure 7C Carbon elemental distribution map of the image. Figure 7C Showing from Figure 7A Image of fluorine distribution elemental map. Distribution of carbon and fluorine in... Figures 7B-7C They are complementary. For example, consider... Figure 7A The particles are outlined by black dashed circles. This position corresponds to... Figures 7B-7C The white dashed circle in the middle, Figure 7B This indicates a decrease in carbon strength. Figure 7C The images show that fluorine is dominant. Fluorine is localized within visible particles, indicating the presence of relatively hydrophobic regions (e.g., co-localization with the presence of PTFE particles). Fluorine-free regions contain relatively hydrophilic areas where the substrate and / or active material (e.g., carbon) are present.

[0100] In some cases, these hydrophobic regions may be at least partially surrounded by hydrophilic regions on the substrate. In some embodiments, at least a portion of the hydrophobic region is at least partially surrounded by a hydrophilic region. In some embodiments, at least a portion of the hydrophobic region is completely surrounded by a hydrophilic region. In some embodiments, the hydrophobic region corresponds to hydrophobic particles (e.g., PTFE particles). Therefore, in some embodiments, the size and distribution of the hydrophobic region on the electrode substrate correspond to the size and distribution of the hydrophobic particles forming the layer. In some cases, the hydrophilic and hydrophobic regions can typically be observed by SEM and subjected to complementary element mapping by EDS, such as... Figures 7B-7C As shown.

[0101] Electrodes can have a variety of suitable electrochemically active geometries. The electrochemically active geometries are two-dimensional areas (as opposed to surface areas considering pores), and can be determined using the geometry of the electrode exposed to the electrolyte solution during use. For example, if the electrochemically active geometries of an electrode exposed to the electrolyte during use have a length of 10 cm and a width of 5 cm, then its total electrochemically active geometries will be 50 cm². 2 In some cases, the electrode has a diameter greater than or equal to 1 cm. 2 ≥2 cm 2 5 cm or greater 2 10 cm or greater 2 50 cm or greater 2 ≥100 cm 2 500 cm or greater 2 ≥1,000 cm 2Or a larger electrochemically active geometric area. In some embodiments, the electrode has a surface area of ​​less than or equal to 2,500 cm². 2 Less than or equal to 2,000 cm 2 Less than or equal to 1,000 cm 2 500cm or less 2 Less than or equal to 100 cm 2 Less than or equal to 50 cm 2 Less than or equal to 10 cm 2 Less than or equal to 5 cm 2 Electrochemically active geometric area less than or equal to 2 cm² or smaller. Combinations of the above ranges are possible.

[0102] According to some embodiments, the electrodes used in this system can be formed by any of a variety of methods. For example, in some cases, the electrode substrate can be pretreated. According to some embodiments, an active material can be applied to the electrode substrate. In some cases, after pretreatment, the electrode can be heated in an inert gas environment (e.g., a non-oxidizing environment) to sinter particles on the electrode and / or remove surfactants from the electrode surface. In some cases, hydrophobic particles are sintered.

[0103] In some embodiments, the substrate (e.g., a nonwoven substrate) may be pretreated. The pretreated electrode may include applying a solution to the substrate, wherein the solution contains hydrophobic particles (e.g., PTFE particles). In some embodiments, PTFE powder and / or micronized powder may be used to pretreat the substrate instead of a PTFE dispersion. In other embodiments, the PTFE particles may be derived from a PTFE dispersion. In some embodiments, the pretreated electrode may make the electrode more hydrophobic and / or may promote, for example, further deposition of a catalytic layer onto the substrate. In some cases, the hydrophobic particles used for the pretreated electrode may be applied to the electrode in a solvent.

[0104] When processing the electrode substrate, various liquids can be used to apply hydrophobic particles. In some embodiments, the liquid is a solvent. According to some embodiments, various solvents can be used to apply hydrophobic particles when pretreating the electrode substrate. In some cases, the solvent may contain an organic solvent. According to some embodiments, the solvent may contain a polar organic solvent. In other cases, the solvent may contain a nonpolar organic solvent. According to some embodiments, the solvent may contain an aprotic polar organic solvent. According to some embodiments, the solvent may contain a protic polar organic solvent. Examples of protic polar organic solvents include, but are not limited to, methanol, ethanol, propanol, butanol, isopropanol, isobutanol, etc. In some cases, it may be advantageous to use a solvent containing isopropanol. In some embodiments, other solvents such as acetone, hexane, chloroform, and / or diethyl ether may be used as solvents during electrode substrate pretreatment. Other non-limiting examples of liquids (e.g., solvents) that can be used include ethyl acetate and / or acetone. In some cases, the solvent may be aqueous and therefore may contain water. Other solvents are also possible. In addition, mixed solvent systems, such as a 50 / 50 mixture of ethanol and isopropanol, may be used. In some cases, mixed solvent systems containing water and alcohol (e.g., IPA) may be used. Other ratios, solvent combinations, and quantities of solvent systems (e.g., at least one component solvent, at least two component solvents, at least three component solvents, etc.) have also been considered, as this disclosure is not limited thereto.

[0105] In some cases, the solvent is a liquid. Certain aspects of solvent selection may relate to its vapor pressure. For example, in some cases, solvents with relatively high vapor pressures may evaporate rapidly after pretreatment of the electrode, which may result in a relatively uniform deposition and associated distribution of hydrophobic particles (e.g., PTFE particles) on the substrate after pretreatment, compared to particle distribution obtained when pretreatment is performed using a relatively low-volatility solvent (e.g., water). In some embodiments, the vapor pressure of the solvent at 25°C may be greater than or equal to 0.1 kPa, greater than or equal to 1 kPa, greater than or equal to 5 kPa, greater than or equal to 10 kPa, greater than or equal to 15 kPa, greater than or equal to 20 kPa, greater than or equal to 25 kPa, or greater than or equal to 30 kPa. In some embodiments, the vapor pressure of the solvent at 25°C may be less than or equal to 35 kPa, less than or equal to 30 kPa, less than or equal to 25 kPa, less than or equal to 20 kPa, less than or equal to 15 kPa, less than or equal to 10 kPa, less than or equal to 5 kPa, or less than or equal to 1 kPa. Combinations of the above ranges are possible (e.g., greater than or equal to 1 kPa and less than or equal to 10 kPa). Other ranges are also possible. Accordingly, some aspects relate to methods for modifying electrodes, wherein the method includes pretreating the electrode by applying a first solution comprising a liquid having a vapor pressure greater than or equal to 1 kPa at 25°C. In some such embodiments, the first solution further comprises a first hydrophobic polymer.

[0106] According to some embodiments, the solution applied to the pretreated electrode may consist only of a solvent and hydrophobic particles. For example, in some such cases, the solution for the pretreated electrode may consist of isopropanol and PTFE particles. In some cases, a surfactant may not be present in the solution. In some such cases, using a relatively volatile solvent and / or not using a surfactant can result in relatively uniform penetration and the resulting hydrophobic particle distribution on the substrate surface after solvent evaporation. In other embodiments, the solution for the pretreated electrode may contain other components, such as surfactants, various solvents, binders, and / or other types of particles. In some embodiments, substrate pretreatment may not be required.

[0107] For example, consider Figure 5BThis illustrates the pretreatment of substrate 580. A pretreatment solution 585 comprising a first hydrophobic polymer 586 may be applied 587 to substrate 580. In some embodiments, multiple applications 588 (e.g., two, three, four, etc.) of the pretreatment solution 585 may allow the hydrophobic polymer 586 to further penetrate into substrate 580 to form a pretreated substrate. It should be understood that the pretreatment solution does not necessarily need to be applied directly to another untreated electrode. In some embodiments, the pretreatment solution may not be applied and / or the pretreatment solution may be applied to an electrode that has been modified by another material (e.g., a catalyst layer). In some cases, such as Figure 5C As shown, a pretreatment liquid is applied to both sides of the substrate, allowing the hydrophobic polymer to further penetrate into the substrate and / or penetrate from both sides of the substrate.

[0108] According to some embodiments, a catalytic layer comprising an active material may be applied to a substrate of an electrode. As described in more detail elsewhere herein, the active material may be applied to the electrode to provide a catalyst for certain electrochemical reactions. According to some embodiments, the catalytic layer may be applied after pretreatment of the electrode. In other cases, the catalytic layer may be applied to the electrode during pretreatment. In some embodiments, the active material may be applied directly to the electrode, for example, as a powder. In some cases, a dispersion of the active material may be deposited on the electrode, for example, to form a catalytic layer. According to some embodiments, the active material may be applied to the substrate of the electrode in the form of a slurry.

[0109] When applying a catalyst layer to a substrate, according to some embodiments, the material of the catalyst layer may initially be present in a solution, suspension, dispersion, or slurry. For example, in some cases, the solution used to apply the catalyst layer may consist only of a solvent and an active material. In some cases, the solution may contain a solvent, an active material, and other components. Solvents such as those used during electrode pretreatment can be used to apply the catalyst layer. Examples of other components include, but are not limited to, hydrophobic polymers, surfactants, and / or binders. In some cases, hydrophobic polymer particles (e.g., PTFE particles) may be provided in the form of dispersions or emulsions, which may act as binders and / or hydrophobic agents in the catalyst layer. In some cases, hydrophobic polymer particles (e.g., PTFE particles) added to the solution, suspension, dispersion, or slurry in the form of dry powder may act as hydrophobic agents and / or binders. In some embodiments, some or all of these components may be present in the solution to be applied to the substrate. In some such cases, the solution may be a slurry.

[0110] Figure 5D-5F An implementation scheme involving substrate treatment with active materials is demonstrated. In some cases, such as... Figure 5D-5EAs shown, the pretreated electrode can be coated with a solution 595 comprising an active material 596 and a second hydrophobic polymer 597 to deposit a catalytic layer on the pretreated substrate 589. In some cases, the pretreated electrode may contain a first hydrophobic polymer before the application of the active material and the second hydrophobic polymer. In some such cases, the first and second hydrophobic polymers are the same polymer. In other such cases, the first and second hydrophobic polymers are different. According to some embodiments, such as Figure 5F As shown, the active material 596 and the second hydrophobic polymer can be applied to a substrate 580 that has not undergone any other treatment. Other embodiments are also envisioned, in which the substrate may be treated with only the active material (e.g., without using the hydrophobic polymer).

[0111] In some embodiments, the electrode can be heated. In some embodiments, the electrode can be heated in a non-oxidizing atmosphere. It has been recognized that, in some cases, heating in an oxidizing environment may result in a relatively hydrophilic substrate, which may be undesirable and could lead to electrode immersion. However, in some cases, the electrode can be heated in an oxidizing environment. In some cases, the electrode can be heated before pretreatment, after pretreatment, and / or after the application of a catalyst layer material to the electrode substrate. According to some embodiments, heating the electrode can provide any of a variety of benefits to the electrode. In some cases, heating the electrode can remove surfactants and / or solvents from the substrate surface of the electrode, which can minimize or prevent the electrode from being submerged. Without wishing to be bound by any particular theory, it is believed that heating the electrode and removing surfactants and / or solvents from the substrate surface of the electrode can make at least a portion of the electrode surface more hydrophobic (e.g., any hydrophobic particles present on the substrate may no longer be covered by relatively hydrophilic surfactants and / or solvents). In some embodiments, heating the electrode in a non-oxidizing atmosphere can reduce the composition of the electrode, making the surface portions relatively hydrophobic and promoting the formation of a three-phase boundary. According to some implementations, the heating electrode can sinter particles present on the electrode substrate, which can provide advantages related to surface hydrophobicity and / or promote the adhesion of particles on the electrode surface.

[0112] In some embodiments, the electrode can be heated to any of a variety of temperatures. In some cases, the electrode can be heated to relatively high temperatures, for example, to obtain greater hydrophobicity of the substrate, better adhesion of particles to the substrate, and / or better removal of surfactants from the electrode. For example, in some embodiments, the electrode can be heated in an atmosphere having an average temperature greater than or equal to 50°C, greater than or equal to 100°C, greater than or equal to 150°C, greater than or equal to 200°C, greater than or equal to 250°C, greater than or equal to 300°C, greater than or equal to 350°C, or greater than or equal to 380°C. In some cases, the electrode can be heated in an atmosphere having an average temperature less than or equal to 400°C, less than or equal to 380°C, less than or equal to 350°C, less than or equal to 300°C, less than or equal to 250°C, less than or equal to 200°C, less than or equal to 150°C, or less than or equal to 100°C. Combinations of the above ranges are possible. Other ranges are also possible.

[0113] According to some embodiments, the atmosphere in which the electrode is heated may contain any of a variety of components. In some cases, the atmosphere may be non-oxidizing. For example, in some cases, the atmosphere in which the electrode is heated contains less than or equal to 1% by weight, less than or equal to 0.1% by weight, and less than or equal to 0.01% by weight of oxygen. In some cases, the atmosphere is substantially oxygen-free. In some cases, the atmosphere may be a reducing atmosphere. In some embodiments, the atmosphere may be dry. Exemplary gases present in the atmosphere include, but are not limited to, N2, CO, H2, and Ar. Vapors may be used in combination with exemplary gases. According to some embodiments, when heating the electrode, a mixture and gases with different proportions of constituent gases may be present in the atmosphere. In some cases, the electrode may be heated in a vacuum (e.g., with a pressure not exceeding 10 kPa, not exceeding 1 kPa, not exceeding 100 Pa, not exceeding 10 Pa, or not exceeding 1 Pa before being heated).

[0114] As described elsewhere herein, in some embodiments, the hydrophobic particles present on the electrode substrate may have any of a variety of sizes. In some cases, heating the electrode may sinter the particles present on the substrate. According to some embodiments, the average maximum cross-sectional area of ​​the hydrophobic particles may increase after heating the electrode. In some cases, the average maximum cross-sectional area of ​​the hydrophobic particles may increase to at least 10%, at least 20%, at least 30%, or at least 40% of the initial average maximum cross-sectional area of ​​the particle distribution. In some embodiments, the average maximum cross-sectional area of ​​the hydrophobic particles may increase to no more than 50%, no more than 40%, no more than 30%, or no more than 20% of the initial average maximum cross-sectional area of ​​the particle distribution. Combinations of the above ranges are possible. Other ranges are also possible. In some cases, heating the electrode may not cause any observable (e.g., measurable) growth of the hydrophobic particles.

[0115] According to some embodiments, after sintering, hydrophobic particles can be grown to have an average maximum cross-sectional size greater than or equal to 100 nanometers, greater than or equal to 500 nanometers, greater than or equal to 1 micrometer, greater than or equal to 3 micrometers, greater than or equal to 5 micrometers, greater than or equal to 10 micrometers, greater than or equal to 25 micrometers, or greater than or equal to 50 micrometers. In some cases, the average maximum cross-sectional size of the hydrophobic particles can be less than or equal to 100 micrometers, less than or equal to 50 micrometers, less than or equal to 25 micrometers, less than or equal to 10 micrometers, less than or equal to 5 micrometers, less than or equal to 3 micrometers, or less than or equal to 1 micrometer. Combinations of the above ranges are possible (e.g., greater than or equal to 1 micrometer and less than or equal to 10 micrometers). Other ranges are also possible.

[0116] As elsewhere in this article Figure 1 The disclosed electrodes can be used in electrochemical systems. These systems can contain various suitable volumes, for example, greater than or equal to 100 cm³. 3 500 cm or greater 3 ≥1,000 cm 3 ≥3,000 cm 3 ≥5,000 cm 3 ≥10,000 cm 3 ≥50,000 cm 3 ≥70,000 cm 3 ≥100,000 cm 3 ≥500,000 cm 3 , greater than or equal to 1 m 3 ≥10 m 3 50 m or greater 3≥100 m 3 Or larger. In some implementations, the volume of the electrochemical system can be less than or equal to 150 m³. 3 Less than or equal to 100 m 3 Less than or equal to 50 m 3 Less than or equal to 10m 3 Less than or equal to 1 m 3 Less than or equal to 500,000 cm 3 Less than or equal to 100,000 cm 3 Less than or equal to 70,000 cm 3 Less than or equal to 50,000 cm 3 Less than or equal to 10,000 cm 3 Less than or equal to 5,000 cm 3 Less than or equal to 3,000 cm 3 Less than or equal to 1,000 cm 3 or less than or equal to 500 cm 3 Combinations of the above ranges are possible. Other ranges are also possible. In some embodiments, the volume of a single electrode stack falls within one of these volume ranges. In some embodiments, the sum of the volumes of all electrode stacks in the system falls within one of these volume ranges. In some embodiments, the sum of the balanced volumes of all electrode stacks, tanks, and facilities employing the electrode stacks in the system falls within one of these volume ranges.

[0117] The electrodes described above can be used as cathodes in an electrochemical system (e.g., in each electrochemical cell of an electrode stack). According to some embodiments, an electrochemical system comprising the electrode structure described herein may further include other components of the electrochemical system.

[0118] For example, in some cases, these electrochemical systems may further include a second electrode, such as an anode. The anode material may comprise any of a variety of materials. For example, the anode may comprise carbon (e.g., graphite), noble metals and oxides or salts (e.g., Pt, Au, Ag), transition metals and oxides or salts (e.g., Ni, Co, Fe) and / or alloys (e.g., stainless steel), Raney nickel, or flame-sprayed materials. Other anode materials may also be used.

[0119] In some cases, the electrochemical system may further include a separator to minimize and / or prevent electrolyte cross-contamination between the anode and cathode electrodes of the battery. In some embodiments, the separator may be a cation exchange membrane. In some cases, the separator may be an anion exchange membrane. In some cases, using a cation exchange membrane as the separator may be advantageous because it can minimize and / or prevent cross-contamination of anions (e.g., perhydroxyl anions, metal-containing polyatomic anions such as zincates) present in the alkaline solution of the electrochemical battery. In some cases, using an anion exchange membrane as the separator may be advantageous to minimize and / or prevent cross-contamination of ions (e.g., metal cations) present in the acidic solution of the electrochemical battery. In some cases, the separator may comprise polyethylene, PTFE, polyvinyl chloride, ceramics, or fluorinated polymers (e.g., perfluorosulfonic acid (PFSA), Nafion). Other separator materials are also possible, as this disclosure is not limited thereto.

[0120] In some embodiments, the electrochemical system may further include a solvent system and / or an electrolyte. In some cases, the solvent system may be organic. In other cases, the solvent system may be aqueous. According to some embodiments, a variety of electrolytes may be used, such as metal ions, halides, acids, bases, and / or polyatomic ions. Exemplary cations include, but are not limited to, H+. + NH4 + Li + Na + K + Ca 2+ and Mg 2+ Examples of anions may include, but are not limited to, F. - Cl - ,Br - I - OH - SO4 2- CO3 2- NO3 - Perhydroxy anion and PO4 3- Other ions are also possible. In some embodiments, certain reduction reactions may proceed more efficiently at a relatively alkaline pH. Depending on the circumstances, a relatively alkaline solution may also be used on the anode side of the electrochemical cell. In some such cases, the electrochemically generated compounds from the anode may be anions and / or form anionic complexes after oxidation at the anode. In some such embodiments, when a cation exchange membrane is used, the electrochemically generated compounds from the anode may not cross the membrane to enter the cathode side of the electrochemical cell when they accumulate a negative charge due to electrolyte conditions.

[0121] Various concentrations of ions in the electrolyte solution used in the anode and / or cathode can be used. For example, in some cases, the ions present in the electrolyte can be present at concentrations of at least 100 mM, at least 500 mM, at least 1 M, at least 1.5 M, at least 2 M, at least 2.5 M, at least 3 M, at least 4 M, at least 5 M, or at least 8 M. In some cases, the electrolyte can be present at concentrations not exceeding 10 M, not exceeding 8 M, not exceeding 5 M, not exceeding 4 M, not exceeding 3 M, not exceeding 2.5 M, not exceeding 2 M, not exceeding 1.5 M, not exceeding 1 M, or not exceeding 500 mM. Combinations of the above ranges are possible. Other ranges are also possible. The electrolyte concentrations in the anode and cathode cells of an electrochemical cell can be different. In some cases, the electrolyte concentration can be selected such that any electrochemically generated compounds do not react within the system, form precipitates, or otherwise decompose.

[0122] According to some embodiments, the system can be configured to allow an electrolyte solution to flow over and / or through at least a portion of the electrodes. In some cases, the system can be configured to allow the electrolyte solution to flow over and / or through at least a portion of each electrode in the electrode stack. In some cases, the electrolyte solution can flow over and / or through each cathode in each electrochemical stack. In some cases, allowing the electrolyte solution to flow can minimize and / or prevent electrochemically generated compounds (e.g., hydrogen peroxide or related ions, or other compounds) from forming steep concentration gradients throughout the electrochemical system, such as near the membrane and / or near the electrodes. In some such cases, avoiding these steep concentration gradients can minimize and / or prevent electrolyte cross-contamination between half-cells (e.g., between the cathode and anode) and / or the formation of precipitates due to relatively high local concentrations of electrochemically generated compounds in the absence of flow. As described in more detail elsewhere herein, in some embodiments, the electrolyte can be recycled throughout the system to further mitigate steep concentration gradients of electrochemically generated compounds.

[0123] According to some embodiments, the electrolyte solution can flow through the system at any of a variety of flow rates. In some cases, using a relatively high flow rate may be advantageous, for example, to increase the mass transport of reactants to the electrode surface of the electrochemical system, to increase the mass transport of electrochemically generated compounds away from the electrode surface, and / or to allow the solution to flow through the pores of a relatively porous electrode (e.g., a carbon-containing nonwoven fiber). Advantageously, in some embodiments, using the electrode structure described herein in the electrochemical system can promote relatively high Faraday efficiency for certain electrochemically generated compounds, thus the concentration gradient of the electrochemically generated compound can be relatively steep near the electrode surface where the compound is electrogenerated. Therefore, a relatively high flow rate can promote the transport of the electrochemically generated compound away from the electrode surface, which can minimize and / or prevent precipitation or substances involving the electrochemically generated compound. According to some embodiments, pressure can be applied to achieve a relatively high flow rate.

[0124] In some cases, the linear flow rate of the electrolyte solution flowing through the electrode can be greater than or equal to 1 mm / s, greater than or equal to 1 cm / s, greater than or equal to 5 cm / s, greater than or equal to 10 cm / s, or greater than or equal to 25 cm / s. In some embodiments, the linear flow rate of the electrolyte solution flowing through the electrode can be less than or equal to 50 cm / s, less than or equal to 25 cm / s, less than or equal to 10 cm / s, less than or equal to 5 cm / s, or less than or equal to 1 cm / s. Combinations of the above ranges are possible. Other ranges are also possible.

[0125] In some cases, the electrolyte solution can flow across the nominal cross-section of the electrode at a rate greater than or equal to 1 mm / s, greater than or equal to 2 mm / s, greater than or equal to 3 mm / s, greater than or equal to 5 mm / s, greater than or equal to 8 mm / s, greater than or equal to 1 cm / s, greater than or equal to 5 cm / s, greater than or equal to 10 cm / s, or greater than or equal to 25 cm / s. In some embodiments, the electrolyte solution can flow across the nominal surface area of ​​the electrode at a rate less than or equal to 50 cm / s, less than or equal to 25 cm / s, less than or equal to 10 cm / s, less than or equal to 5 cm / s, less than or equal to 1 cm / s, less than or equal to 8 mm / s, less than or equal to 5 mm / s, less than or equal to 3 mm / s, or less than or equal to 2 mm / s. Combinations of the above ranges are possible. Other ranges are also possible.

[0126] In some implementations, the flow rates on each side of the electrochemical system (e.g., the cathode side relative to the inner side) can differ, for example, based on the electrodes present on each side of the electrochemical system. For instance, in some cases, a relatively porous electrode can be used on the cathode side, resulting in a higher flow rate; while a planar electrode can be used on the anode side, resulting in a lower flow rate. Other implementations have different electrode structures on both sides of the electrochemical system, and different flow rates can be used depending on the pressure drop associated with each electrode structure and the configuration of the electrochemical system. As described elsewhere herein, multiple pumps, mass flow controllers, sensors, etc., can be used to achieve different flow rates in different compartments of the electrochemical system.

[0127] According to some embodiments, the cathode side of the electrochemical cell may be fluidly connected to a circulation tank. In some embodiments, each cathode in the electrode stack may be fluidly connected to the circulation tank. In some cases, compounds electrocatalytically generated at the cathode flow from the cathode to the circulation tank. In some such cases, the amount of electrochemically generated compounds at the cathode may remain relatively constant over time while the absolute value of the current density at the cathode remains constant. Therefore, in some such cases, while maintaining the current density at the cathode, the solution flowing from the cathode into the circulation tank may contain a relatively constant amount of electrochemically generated compounds. In some cases, the circulation tank may further include a second inlet through which fresh cathode electrolyte (e.g., cathode electrolyte without electrochemically generated compounds, such as water) may be added, and / or an outlet through which a solution containing electrochemically generated compounds may be discharged.

[0128] According to some embodiments, the volume of the solution in the circulating tank can be maintained at a constant level, the concentration of the compound in the circulating tank can be maintained at a constant level (e.g., after a relatively constant current density is applied at the cathode and the system reaches equilibrium), and / or a portion of the compound can be discharged from the system (e.g., through an outlet) during continuous operation of the system. As described elsewhere herein, the flow rates through the cathode side of the electrochemical cell and the first inlet of the circulating tank, the flow rate through the second inlet of the circulating tank, and the flow rate through the outlet of the circulating tank can vary depending on the desired current density at the cathode and / or the desired rate of compound removal from the system.

[0129] The system may further include any of a variety of sensors. In some cases, sensors for measuring the flow rate into and / or out of electrochemical system components (e.g., electrode stacks, cathode reservoirs, anode reservoirs) may be used. Other sensors may also be used, such as sensors for measuring the concentration of substances in a solution (e.g., the concentration of electrochemically generated compounds). In some embodiments, a solution sample may be removed from the electrochemical system and tested outside the system to determine the concentration of substances in the solution. In some embodiments, sensors may be present to determine the formation and / or presence of undesirable materials (e.g., precipitates). According to some embodiments, substances such as precipitates may be observed by optical means (e.g., spectroscopy) and / or by increasing resistance or other electrical methods. Other methods are also possible. Sensors may provide real-time feedback and / or communicate with processors and / or controllers to adjust system parameters in real time to improve system efficiency, such as flow rate and / or the density of applied current. In some cases, the system may include a flow sensor but not other types of sensors. Other systems do not include any sensors.

[0130] According to some embodiments, a method comprising the steps of: mixing a liquid and a gas to form a two-phase solution, allowing the two-phase solution to flow over and / or through at least a portion of an electrode containing a substrate, and applying a voltage to the electrode such that at least a portion of the gas participates in a reaction to electrochemically generate a compound at the electrode. In some cases, the solution containing the electrochemically generated compound is recycled to a compartment containing the electrode, at least until the content of the compound in the solution is greater than or equal to 2% by weight. For example, refer again... Figure 3 -4 allows two-phase solutions to flow through the cathode substrate of an electrochemical cell, which may exist in an electrode stack.

[0131] According to some implementation schemes, the use of two-phase solutions can facilitate electrocatalytic reactions involving gaseous and liquid reactants. It is believed that the use of two-phase solutions can promote the formation of a three-phase interface on the electrode surface (e.g., on the outer surface of the electrode and / or in the pore space of the electrode). In some cases, a two-phase solution typically refers to two different phases (e.g., gas and liquid) flowing simultaneously and dispersed among themselves.

[0132] The properties of a two-phase solution may depend on the relative flow rates of the constituent phases, the properties of the phases, and / or the interaction between the phases and the system (e.g., the fluid channels that transport the two-phase solution, electrode structures, etc.).

[0133] In some embodiments, the liquid can be flowed at any of a variety of rates to the junction where a two-phase solution can be formed. In some cases, the liquid flow rate may depend on the volume of the system. In some embodiments, the liquid can flow to the junction where a two-phase solution can be formed at a rate greater than or equal to 0.2 mL / min, greater than or equal to 0.5 mL / min, greater than or equal to 1 mL / min, greater than or equal to 2 mL / min, greater than or equal to 5 mL / min, greater than or equal to 30 mL / min, greater than or equal to 50 mL / min, greater than or equal to 100 mL / min, greater than or equal to 500 mL / min, greater than or equal to 1,000 mL / min, or greater than or equal to 2,500 mL / min. In some cases, the liquid can flow at rates less than or equal to 5,000 mL / min, less than or equal to 2,500 mL / min, less than or equal to 1,000 mL / min, less than or equal to 500 mL / min, less than or equal to 100 mL / min, less than or equal to 50 mL / min, less than or equal to 30 mL / min, less than or equal to 5 mL / min, less than or equal to 2 mL / min, less than or equal to 1 mL / min, or less than or equal to 0.5 mL / min. Combinations of the above ranges are possible. Other ranges are also possible.

[0134] In some embodiments, the gas can be flowed to the junction at various flow rates, where a two-phase solution can be formed. In some cases, the liquid mass flow rate can depend on the system volume. In some embodiments, the gas can be flowed to the junction at a mass flow rate greater than or equal to 0.2 standard liters per minute (slpm), greater than or equal to 1 slpm, greater than or equal to 1 slpm, greater than or equal to 5 slpm, greater than or equal to 10 slpm, greater than or equal to 25 slpm, or greater than or equal to 35 slpm to form a two-phase solution. In some cases, the liquid can flow at a flow rate less than or equal to 50 slpm, less than or equal to 35 slpm, less than or equal to 25 slpm, less than or equal to 10 slpm, less than or equal to 5 slpm, less than or equal to 1 slpm, or less than or equal to 0.5 slpm. Combinations of the above ranges are possible. Other ranges are also possible.

[0135] In some cases, the ratio of the gas present in the two-phase solution to the amount of gas converted into a compound in the electrocatalytic reaction can be greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, or greater than or equal to 9. In other cases, the ratio of the gas present in the two-phase solution to the amount of gas converted into a compound in the electrocatalytic reaction can be less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, less than or equal to 5, less than or equal to 4, or less than or equal to 3. Combinations of the above ranges are possible (e.g., greater than or equal to 1 and less than or equal to 10, greater than or equal to 4 and less than or equal to 6). Other ranges are also possible.

[0136] According to some embodiments, electrocatalysis performed in the system described herein involves flowing a solution over and / or through at least one electrode in the system. For example, as described elsewhere herein, the system may comprise an electrode having a substrate, pretreatment of hydrophobic particles (e.g., PTFE particles), and a catalytic layer comprising active material and / or hydrophobic particles. In some such embodiments, pressurized flow may be used to facilitate the flow of the solution over and / or through at least one electrode in the system. In some embodiments, pressurized flow of a two-phase solution may facilitate its use in conjunction with the electrode structure described herein.

[0137] To achieve pressurized flow of fluid on and / or through the system electrodes, in some embodiments, any of a variety of methods may be employed. For example, in some embodiments, fluid pumps (e.g., peristaltic pumps, diaphragm pumps, gear pumps, centrifugal pumps, rotary vane pumps), compressed gases, hydraulic systems, or pneumatic systems may be used. Liquid ring compressors are particularly advantageous in providing pressure to gases. In some cases, liquid ring compressors can humidify the gas. Other methods may also be used, as this disclosure is not limited thereto. In some cases, mass flow controllers and / or mass flow sensors may be coupled to methods for pressurized flow to achieve a specific flow rate on and / or through at least one electrode of the system.

[0138] According to some embodiments, various pressures can be used. In some cases, the pressure can be varied to achieve different flow rates of the solution at and / or through the system electrodes. According to some embodiments, different flow rates may be desired based on a number of factors, including mass transport of reactants to the electrodes, mass transport of electrochemically generated compounds away from the electrodes, and / or maintaining a certain current density at the electrodes, as described in more detail elsewhere herein.

[0139] In some embodiments, recycling the cathode electrolyte and / or anolyte after they have passed through and / or traversed the cathode and anode, respectively, can provide any of a number of advantages. For example, in some cases, recycling electrochemically generated compounds from the anode and / or cathode in the system can reduce the concentration gradient of such electrochemically generated compounds near the anode or cathode. According to some such embodiments, this can reduce and / or eliminate the formation of precipitates including and / or involving the electrochemically generated compounds.

[0140] For example, such as Figure 1 As shown, solutions containing electrochemically generated compounds flowing from outlets A8 and C4 of the cathode or anode can flow into storage tanks A4 and C5. Electrochemically generated compounds collected in at least one storage tank can be separated from and / or discharged from the storage tank via outlets on the tank. In some embodiments, when the electrochemically generated compound is in solution (e.g., dissolved in solution), the electrochemically generated compound can be removed (e.g., from the system) via an outlet (e.g., a drain or pipe) suitable for the flow of the solution. In some embodiments, when the electrochemically generated compound is in a gaseous state (e.g., a gas undissolved in solution), the electrochemically generated compound can be removed via an outlet (e.g., a vent) suitable for the flow of gas. For example, a solution from the cathode storage tank is removed via outlet C6 to obtain a solution containing the electrochemically generated compound. As an alternative to the removed solution, a fresh reactant solution (e.g., a solution having substantially the same composition as the solution flowing through the electrode before electrogenesis of any compound, and / or an aqueous solution substantially free of electrochemically generated compounds) can be added to the reservoir via inlet C1. This helps maintain a constant level of electrochemically generated compounds within the reservoir (e.g., a cathode reservoir) when the system is operating in steady state. In some embodiments, the water added to the reservoir is deionized (DI) water.

[0141] Figure 1 The system shown offers various advantages; for example, its configuration promotes the recycling of compounds in the cathodic electrolyte (as shown, or in an alternative embodiment, the anodic electrolyte), thus minimizing the concentration gradient of electrochemically generated compounds near the cathode. Furthermore, Figure 1The system shown facilitates continuous operation while simultaneously extracting electrochemically generated compounds via, for example, outlet C6 of cathode electrolyte reservoir C5. In this manner, the rate at which electrochemically generated compounds are extracted from cathode electrolyte reservoir C5 using outlet C6 and inlet C1 can be based on the flow rate of the cathode electrolyte solution through outlet C6. In some such cases, if the removal rate of electrochemically generated compounds through the outlet is balanced with the rate of electrochemical generation of compounds at the electrodes (e.g., determined by current density), the concentration of electrochemically generated compounds throughout the system can be maintained at a relatively constant value during steady-state operation.

[0142] In some embodiments, due to the relatively high flow rates used in the system, the solution flowing into the storage tank from the system outlet may initially contain relatively small amounts of electrochemically generated compounds. For example, in some systems where hydrogen peroxide is electrochemically generated, hydrogen peroxide may be generated in the solution at concentrations not exceeding 2 wt%, 1 wt%, 0.8 wt%, 0.6 wt%, 0.4 wt%, 0.2 wt%, 0.1 wt%, 0.08 wt%, 0.05 wt%, 0.03 wt%, 0.01 wt%, 0.008 wt%, 0.005 wt%, or 0.003 wt% when the solution flows out of the outlet of the electrochemical system after a single pass through the cathode (e.g., the cathode in the electrode stack). In some such cases, it may be advantageous to recycle the solution from the system to accumulate more electrochemically generated compounds in the solution flowing through the system. In some embodiments, the system may be configured to not withdraw the solution from the storage tank until a certain amount of electrochemically generated compounds are present in the electrolyte solution recirculated through the system (e.g., present in the storage tank).

[0143] According to some implementation schemes, electrochemically generated compounds (e.g., desired, value-added electrochemically generated compounds, such as hydrogen peroxide) can be recycled through the system without removing any electrochemically generated compounds (e.g., via...). Figure 1The solution may contain, for example, an outlet (C5) from which the electrochemically generated compound is present in the solution at a predetermined concentration. In addition to the desired high-value electrochemically generated compound, other compounds may also be present in the solution. These compounds may be electrochemically generated and / or participate as charge carriers in the electrochemical generation of the desired compound (e.g., NaOH may be present in the solution and participate in the electrochemical generation of hydrogen peroxide and / or may be generated by the electrochemical reaction itself). The concentration ranges described in the following paragraphs should not be construed as limiting the amount of these additional compounds. For example, a solution containing an electrochemically generated compound may flow out from the outlet of a compartment containing an electrode, where the electrochemically generated compound is electrochemically generated at that electrode. According to some such embodiments, at least a portion of the solution from the outlet may be recycled from the outlet to the inlet of the compartment, such that the electrochemically generated compound is present in the solution at a predetermined concentration. In some embodiments, the amount of the electrochemically generated compound present in solution during recycling is greater than or equal to 0.2 wt%, greater than or equal to 0.4 wt%, greater than or equal to 0.6 wt%, greater than or equal to 0.8 wt%, greater than or equal to 1 wt%, greater than or equal to 1.5 wt%, greater than or equal to 2 wt%, greater than or equal to 3 wt%, greater than or equal to 4 wt%, greater than or equal to 5 wt%, or greater than or equal to 6 wt%. In some cases, the amount of the electrochemically generated compound present in solution during recycling is less than or equal to 7 wt%, less than or equal to 6 wt%, less than or equal to 5 wt%, less than or equal to 4 wt%, less than or equal to 2 wt%, less than or equal to 1.5 wt%, less than or equal to 1 wt%, less than or equal to 0.8 wt%, less than or equal to 0.6 wt%, or less than or equal to 0.4 wt%. Combinations of the above ranges are possible (e.g., greater than or equal to 2 wt% and less than or equal to 7 wt%). Other ranges are also possible.

[0144] According to some implementations, the electrochemically generated compound can be circulated in the system without removing any of the electrochemically generated compound (e.g., via...). Figure 1The electrochemically generated compound is present in the solution at a predetermined concentration, such as at least 0.2 wt%, at least 0.4 wt%, at least 0.6 wt%, at least 0.8 wt%, at least 1 wt%, at least 1.5 wt%, at least 2 wt%, at least 3 wt%, at least 4 wt%, at least 5 wt%, or at least 6 wt%. In some cases, the solution can be recycled without removing any electrochemically generated compound from the solution until the amount of the electrochemically generated compound in the solution does not exceed 7 wt%, 6 wt%, 5 wt%, 4 wt%, 2 wt%, 1.5 wt%, 1 wt%, 0.8 wt%, 0.6 wt%, or 0.4 wt%. Combinations of the above ranges are possible (e.g., greater than or equal to 2 wt% and less than or equal to 6 wt%). Other ranges are also possible. In some embodiments, once the desired amount of the electrochemically generated compound is reached in the circulating solution, it can be discharged through an outlet (e.g., as shown in the image). Figure 1 The outlet C6 of the cathode electrolyte reservoir shown removes at least a portion of the electrochemically generated compound from the circulating solution. In some embodiments, as described elsewhere herein, a fresh solution (e.g., deionized water and / or a solution not containing the electrochemically generated compound) can be introduced into the reservoir through inlet C1 at the same rate as the solution being removed from the reservoir. In some embodiments, this provides a method for continuously producing a solution containing the electrochemically generated compound at a desired concentration.

[0145] Figure 8A general flow chart 800 related to the circulation of electrolyte in an electrochemical system for generating hydrogen peroxide is shown. This disclosure is not limited to this; other embodiments for the electrogeneration of other compounds are also possible. Raw materials, such as deionized (DI) water or water having at least a certain resistivity as described elsewhere herein, and / or other electrolyte components and / or reactants, may flow into an electrochemical stack 804 (e.g., a peroxide stack, the electrochemical system). Peroxides (e.g., other compounds in other systems) can be electrochemically generated by applying a current density 806 to the electrochemical stack 804 via a power source. Electrochemical generation of compounds such as peroxides, in some cases, refers to applying a voltage to electrodes to facilitate reduction and / or oxidation reactions at the electrodes. In some such embodiments described herein, such as peroxide generation, at least one reactant is reduced and / or oxidized at an electrode, and then that reactant can react with another substance in solution to form the final electrochemically generated compound. In some cases, a solution containing the electrochemically generated product may flow to a reservoir 810 (e.g., a cathode electrolyte tank), where it can be recycled back to the peroxide stack. When the solution is recycled, the electrochemically generated compound can be diluted before recycling by mixing with feedstock 802. In some cases, after the compound is electrochemically generated, some of the compound can be removed from solution 808 for use elsewhere. According to some embodiments, recycling can continue until the desired concentration of the electrochemically generated compound is present in the electrolyte solution before removing the electrochemically generated compound 808. For example, feedstock may not be continuously introduced into system 802 until the electrochemically generated compound is being withdrawn from 808, in order to maintain a relatively constant concentration of the electrochemically generated compound in the system.

[0146] Some aspects of this disclosure relate to methods of using and / or operating the systems described herein.

[0147] According to some embodiments, the electrode structures described elsewhere herein can be used in these systems, such as electrodes comprising a substrate. In some cases, the electrode structures disclosed herein can facilitate the formation of a three-phase boundary at which certain electrochemical reactions (e.g., oxygen reduction) can occur. As disclosed elsewhere herein, it is believed that discrete hydrophilic and hydrophobic regions on the electrode surface promote the formation of such a three-phase interface.

[0148] In some embodiments, to maintain discrete hydrophobic and hydrophilic regions on the electrode (e.g., hydrophilic active materials such as carbon and / or hydrophobic particles such as PTFE particles), it may be advantageous to keep the electrode dry when not in use (i.e., having minimal or no continuous phase of water on and / or throughout the electrode substrate). In some cases, it may be advantageous to allow a gas to flow through the electrode structure before allowing a solution to flow on and / or through the electrode. In some cases, the gas may be dry. In some cases, the gas may have a relative humidity greater than or equal to 50%, greater than or equal to 75%, greater than or equal to 90% up to 100%. In some embodiments, the gas may contain O2, N2, H2, Ar, etc. Other gases are also possible. Gas combinations are also possible, wherein these combinations have various proportions of constituent gases.

[0149] According to some embodiments, after the gas is allowed to flow, the solution can be allowed to flow over and / or through the electrode. In some embodiments, the flowing solution contains water. It should be understood that when water is described as flowing (e.g., flowing through a portion of the electrochemical system and / or over and / or through the electrode), the water can be in the form of pure water or can be mixed with one or more additional substances (e.g., as part of an aqueous solution). These additional substances can be, for example, solutes such as NaOH or other softeners. In some embodiments, the flowing water contains softened water. In some embodiments, the flowing water contains deionized water. In some embodiments, the solution may consist of deionized water. In some embodiments, the solution may flow over and / or through the electrode together with the gas. In some embodiments, the solution may contain an electrolyte solution, such as a solution containing water and electrolyte ions (e.g., dissociated NaOH, as described elsewhere herein).

[0150] In some cases, using the systems disclosed herein, electrochemical reactions at the electrodes can occur in a relatively efficient manner. For example, in some embodiments, the electrochemical reactions can proceed with relatively high Faraday efficiency and a low percentage of byproducts. According to some embodiments, the electrochemical reactions can proceed without the application of a significant amount of overpotential compared to the thermodynamic reduction potential of the reaction. Advantageously, in some such cases, although the kinetics of the reactions (e.g., oxygen reduction, CO2 reduction, etc.) are relatively slow, for example due to the electrode structure described herein and / or the disclosed systems (e.g., flowing two-phase solutions), the electrochemical reactions can still occur without the application of a significant amount of overpotential.

[0151] In some cases, the Faradaic efficiency of at least one reaction in an electrochemical system may be relatively high. In some embodiments, the Faradaic efficiency of reduction reactions (e.g., the two-electron reduction of oxygen to hydrogen peroxide) in an electrochemical system may be relatively high, for example, due to electrode structure and / or system design using a two-phase solution. According to some embodiments, the Faradaic efficiency of at least one reaction in an electrochemical system can be greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, greater than or equal to 98%, greater than or equal to 99%, greater than or equal to 99.5%, or greater than or equal to 99.9%. In some such cases, the Faradaic efficiency may refer to the reduction reaction (e.g., the reduction of oxygen to hydrogen peroxide). In some such cases, the Faradaic efficiency may refer to the oxidation reaction.

[0152] Accordingly, in some embodiments, because the Faraday efficiency of the at least one reaction in the electrochemical system is relatively high, a relatively low overpotential can be used to obtain a relatively high current density at the electrodes of the system. For example, in some cases, the overpotential input to the system relative to the thermodynamic reduction potential of a half-reaction (e.g., a reduction reaction) can be less than or equal to 500 mV, less than or equal to 400 mV, less than or equal to 300 mV, less than or equal to 200 mV, less than or equal to 100 mV, less than or equal to 50 mV, or less than or equal to 20 mV. In some cases, the overpotential input to the system relative to the thermodynamic potential difference between the two half-cells (e.g., between the anodic and cathodic reactions) can be less than or equal to 1 V, less than or equal to 900 mV, less than or equal to 800 mV, less than or equal to 700 mV, less than or equal to 600 mV, less than or equal to 500 mV, or lower. In some implementations, the overpotential of the input system may be related to the nature of the half-reaction, the potential loss due to the presence of the membrane, concentration polarization, and / or operating conditions (e.g., current density, temperature, etc.).

[0153] In some embodiments, the relatively high Faraday efficiency of the electrode structures and / or systems described herein for certain electrochemical reactions may facilitate the application of relatively high current densities at the electrodes in the system without significant energy loss and / or the generation of substantial byproducts. In some cases, the absolute value of the current density at the electrodes (e.g., at the cathode, for example during the oxygen reduction reaction; calculated using the projected 2-D area of ​​the untreated substrate) can be greater than or equal to 20 mA / cm². 2 ≥50 mA / cm 2 ≥100 mA / cm 2 ≥150 mA / cm 2 ≥200 mA / cm 2 ≥300 mA / cm 2≥400 mA / cm 2 ≥500 mA / cm 2 ≥600 mA / cm 2 ≥700 mA / cm 2 or greater than or equal to 800 mA / cm 2 In some implementations, the absolute value of the current density at the electrode can be less than or equal to 800 mA / cm². 2 Less than or equal to 700 mA / cm 2 Less than or equal to 600 mA / cm 2 Less than or equal to 500 mA / cm 2 Less than or equal to 400 mA / cm 2 Less than or equal to 300 mA / cm 2 Less than or equal to 200 mA / cm 2 Less than or equal to 150 mA / cm 2 Less than or equal to 100 mA / cm 2 or less than or equal to 50 mA / cm 2 Combinations of the above ranges are possible. Other ranges are also possible.

[0154] In some embodiments, the system can be configured to electrochemically generate substances (e.g., hydrogen peroxide) at various potential differences. In some embodiments, the system can be configured to electrochemically generate substances at voltages less than or equal to 4.5 V, less than or equal to 4 V, less than or equal to 3.5 V, less than or equal to 3 V, less than or equal to 2.5 V, less than or equal to 2.25 V, less than or equal to 2 V, less than or equal to 1.75 V, less than or equal to 1.5 V, less than or equal to 1.45 V, less than or equal to 1.4 V, less than or equal to 1.35 V, less than or equal to 1.3 V, less than or equal to 1.25 V, less than or equal to 1.2 V, less than or equal to 1.15 V, less than or equal to 1.1 V, less than or equal to 1.05 V, less than or equal to 1 V, or lower. In some embodiments, the voltage described in this disclosure is applied between the cathode and anode, for example, in a two-electrode cell.

[0155] In some cases, when the system is operating in steady state, the electrochemical reactions in the system can occur at a specific current density (e.g., greater than or equal to 150 mA / cm²). 2While the process can proceed under normal conditions, it may be advantageous to slowly increase the absolute value of the current density during system startup. For example, in some cases, slowly increasing the absolute value of the current density can gradually heat the system (e.g., the solution flowing through the system), thereby preventing and / or minimizing the amount of precipitates that may form in the system. In some cases, the system can be heated by Joule heating. In some embodiments, the system may include a built-in heater, such as a resistance heating coil and / or a heat exchanger. Other heaters are also possible. According to some embodiments, the solution may be heated before flowing through the system. In some cases, the absolute value of the current density can be increased in a linear ramp function, a step function, an exponential function, etc.

[0156] In some cases, the absolute value of the current density can be greater than or equal to 3 mA / cm². 2 / min, greater than or equal to 25 mA / cm 2 / min, greater than or equal to 50 mA / cm 2 / min, greater than or equal to 100 mA / cm 2 / min or greater than or equal to 150mA / cm 2 The current density increases at a rate of / min. In some implementations, the absolute value of the current density can be less than or equal to 200 mA / cm². 2 / min, less than or equal to 150 mA / cm 2 / min, less than or equal to 100 mA / cm 2 / min, less than or equal to 50 mA / cm 2 / min or less than or equal to 25 mA / cm 2 The rate of increase is [ / min]. The absolute value of the current density can be increased until the desired absolute current density required for operation of the electrochemical system is reached. Combinations of the above ranges are possible. Other ranges are also possible. In some embodiments, the desired current density for operation of the electrochemical system can be at least 150 mA / cm². 2 At least 175 mA / cm 2 At least 200 mA / cm 2 At least 225 mA / cm 2 At least 250 mA / cm 2 At least 275 mA / cm 2 At least 300 mA / cm 2 At least 325 mA / cm 2 At least 350 mA / cm 2 At least 375 mA / cm 2 Or at least 400 mA / cm 2 and / or not exceeding 425 mA / cm2 1. Not exceeding 450 mA / cm² 2. Not exceeding 475 mA / cm² 2 Not exceeding 500 mA / cm 2 Not exceeding 525 mA / cm 2 Not exceeding 550mA / cm 2 Not exceeding 575 mA / cm 2 or not exceeding 600 mA / cm 2 .

[0157] Therefore, in some cases, the absolute value of the current density can be greater than or equal to 15 mA / cm². 2 ≥20 mA / cm 2 ≥25 mA / cm 2 ≥30 mA / cm 2 ≥50 mA / cm 2 ≥100 mA / cm 2 ≥125 mA / cm 2 ≥250 mA / cm 2 ≥500 mA / cm 2 or greater than or equal to 750 mA / cm 2 The rate increases every 5 minutes. In some implementations, the absolute value of the current density can be less than or equal to 1,000 mA / cm². 2 Less than or equal to 750 mA / cm 2 Less than or equal to 500 mA / cm 2 Less than or equal to 250 mA / cm 2 Less than or equal to 125 mA / cm 2 Less than or equal to 100 mA / cm 2 Less than or equal to 75 mA / cm 2 Less than or equal to 50 mA / cm 2 or less than or equal to 40 mA / cm 2 The rate increases every 5 minutes. The absolute value of the current density can be increased until the desired absolute current density required for the operation of the electrochemical system is reached. Combinations of the above ranges are possible.

[0158] After an initial increase in the absolute value of the current density, the average temperature of the solution and / or system may be raised (e.g., by Joule heating) to greater than or equal to 25°C, greater than or equal to 30°C, greater than or equal to 35°C, or greater than or equal to 40°C, before the absolute value of the current density is increased again. In some cases, the average temperature of the solution and / or system may be raised to less than or equal to 45°C, less than or equal to 40°C, less than or equal to 35°C, or less than or equal to 30°C to change the absolute value of the current density again. Combinations of the above ranges are possible. Other ranges are also possible.

[0159] Some aspects of the aforementioned methods involve improving system efficiency and / or minimizing and / or preventing the formation of precipitates in the system. In some cases, after 6 hours of continuous system operation, the amount of precipitate formed in the system may be less than or equal to 10 g, less than or equal to 1 g, less than or equal to 0.1 g, or less than or equal to 0.01 g. In some embodiments, the precipitate may contain sodium peroxide hydrate. In some cases, the precipitate may contain Fe and / or Ni. In some embodiments, the precipitate may contain iron oxide. According to some embodiments, the precipitate may contain Fe2O3. In some cases, the precipitate may contain nickel oxide and / or nickel hydroxide. In some cases, the precipitate contains NiO and / or Ni(OH)2 and / or NiOOH. Other precipitates may also be present. In some embodiments, the exact identity of the precipitate may be unknown.

[0160] In some implementations, when precipitates form at a relatively slow rate (e.g., 0.01 g precipitate / 6 hours of operation), precipitates may accumulate during long-term system operation. The inventors have recognized in the context of this invention that regular cleaning of the system can provide certain advantages, such as precipitate removal and / or extended system lifespan.

[0161] In some embodiments, precipitates may form at the junction of the gas and liquid injection points. According to some embodiments, a humidifying gas is used to prevent precipitate formation. Using a liquid ring compressor may be advantageous because it naturally humidifies the reactant gases during operation. According to some embodiments, the gas injected at the junction is inert. For example, the gas may contain N2 and / or Ar. In some embodiments, the gas contains O2 and / or H2. Other gases and / or gas combinations are also possible. In some embodiments, it is desirable for the gas to contain very little or no CO2, as CO2 can form an alkaline solution and cause precipitate formation when the two-phase solution is flowing. In some embodiments, the gas is CO2-free or contains CO2 in amounts less than or equal to 5% by weight, less than or equal to 4% by weight, 3% by weight, less than or equal to 2% by weight, less than or equal to 1% by weight, less than or equal to 0.1% by weight, less than or equal to 0.01% by weight, less than or equal to 0.001% by weight, less than or equal to 0.0001% by weight, or less.

[0162] In some cases, the system can electrochemically generate compounds, and then the absolute value of the system's current density can be reduced to less than or equal to 1 mA / cm². 2 Less than or equal to 0.1 mA / cm 2 Or even less, for example, reduced to 0 mA / cm 2 In some embodiments, to remove precipitates, a solution containing a reducing agent and / or a chelating agent (e.g., a cleaning solution) may be flowed through the system. In some embodiments, the solution is an aqueous solution containing water and one or more solutes (e.g., electrolytes, NaOH, or other softeners). In other embodiments, the solution may be additive-free deionized water. In some cases, the solution may flow through the system as a two-phase solution along with a gas. In other embodiments, the solution may flow through the system without a gas. It should be understood that in some cases, when a solution (e.g., a cleaning solution, a solution containing a reducing agent and / or a chelating agent, an aqueous solution, deionized water) flows through the system, the solution may interact with chemicals (e.g., solutes or other substances (e.g., precipitates)). In some embodiments, interaction with a substance (e.g., a solute) may involve dissolving and / or suspending the substance. Therefore, in some embodiments, the solution flowing through the system contains a solute and / or forms a suspension containing solid matter suspended in the solution.

[0163] When a solution (e.g., a cleaning solution, a solution containing a reducing agent and / or a chelating agent, an aqueous solution, deionized water) flows through the system together with a gas to form a two-phase solution, in some embodiments, the gas is inert. For example, the gas may contain N2 and / or Ar. In some embodiments, the gas contains O2 and / or H2. Other gases and / or combinations of gases are also possible. In some embodiments, it is desirable for the gas to contain very little or no CO2, as CO2 can form an alkaline solution and cause precipitate formation when the two-phase solution flows. In some embodiments, the gas contains no CO2 or contains CO2 in an amount less than or equal to 5% by weight, less than or equal to 4% by weight, 3% by weight, less than or equal to 2% by weight, less than or equal to 1% by weight, less than or equal to 0.1% by weight, less than or equal to 0.01% by weight, less than or equal to 0.001% by weight, less than or equal to 0.0001% by weight, or less.

[0164] In some embodiments, the reducing agent in the solution used to treat one or more electrodes (e.g., to remove precipitates, remove contaminants, and / or increase hydrophobicity) comprises a sulfur-containing reducing agent. For example, the reducing agent may comprise hyposulfite, metabisulfite, thiosulfate, sulfite, and / or bisulfite anions (e.g., having counter anions such as sodium cations, potassium cations, or ammonium cations). In some embodiments, the reducing agent comprises an organic reducing agent, such as an organic acid. Examples of such reducing agents include, but are not limited to, ascorbic acid and / or oxalic acid. In some embodiments, the reducing agent in the solution used to remove precipitates may comprise sodium bisulfite, sodium metabisulfite, and / or sodium sulfite. In some embodiments, the reducing agent comprises bisulfite anions (e.g., sodium bisulfite), ascorbic acid, oxalic acid, and / or thiosulfate anions (e.g., sodium thiosulfate). In some embodiments, the reducing agent comprises sodium bisulfite. Other reducing agents are possible. In some cases, the solution used to remove precipitates may contain a chelating agent, such as citric acid. In some embodiments, the chelating agent comprises NTA, TPP, citric acid, and / or EDTA. In some embodiments, the chelating agent comprises EDTA. Other chelating agents are also possible.

[0165] According to some implementations, the solution can continuously flow through the system to clean it for at least 20 seconds and no more than 7 days. In some cases, such system cleaning can be performed at least once a year and no more than once a day. According to some implementations, the solution (e.g., a cleaning solution, a solution containing a reducing agent and / or a chelating agent, an aqueous solution, deionized water) can continuously flow through the system to clean it for at least 20 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 30 minutes, at least 1 hour, at least 2 hours, at least 3 hours, at least 6 hours, or at least 12 hours and / or no more than 1 day, no more than 2 days, no more than 3 days, no more than 4 days, no more than 5 days, no more than 6 days, or no more than 7 days. In some cases, such system cleaning can be performed at least once a year and no more than once a day.

[0166] In some cases, water can be flowed through the system after cleaning it with a solution containing reducing agents and chelating agents. In some embodiments, the water flowing through the system is deionized water. It should be understood that in some cases, when water (e.g., deionized water) flows through the system, the water may interact with chemicals (e.g., solutes) or other substances (e.g., precipitates). In some embodiments, interaction with a substance (e.g., solute) may involve dissolving and / or suspending that substance. Therefore, in some embodiments, the water (e.g., deionized water) flowing through the system may form a solution containing a solute and / or a suspension containing solids suspended in the water. Water (e.g., deionized water) may co-flow through the system with a gas, for example, to form a two-phase solution, thereby removing any residual precipitates and / or cleaning the solution and preventing the cathode electrode structure from being submerged. According to some embodiments, the liquid phase of the two-phase solution may interact with a substance such as a solute to form a solution containing that solute and / or a suspension containing that solid. In some embodiments, the flow of cleaning solution followed by water (e.g., deionized water) may be performed immediately before operating the system and / or before shutting it down.

[0167] In some embodiments, after reducing the absolute value of the applied current density in the electrochemical system, the solution is allowed to flow through the system for at least 1 minute, at least 5 minutes, or at least 10 minutes. In some cases, the solution contains an electrolyte used during operation of the electrochemical system. In some embodiments, the solution contains water with a resistivity greater than or equal to 1 megohmcm, greater than or equal to 10 megohmcm, or higher at 25°C. In some embodiments, the solution contains water with a resistivity greater than or equal to 15 megohmcm, greater than or equal to 17 megohmcm, greater than or equal to 18 megohmcm, or greater than or equal to 18.2 megohmcm at 25°C. In some embodiments, the solution flows through at least a portion of the electrochemical system described herein. In some embodiments, the solution is an aqueous solution and can flow through at least a portion of the system, wherein the aqueous solution has a resistivity corresponding to any of the above ranges. In some embodiments, the aqueous solution contains water and one or more solutes (e.g., NaOH, other softening agents). In some embodiments, deionized (DI) water can be allowed to flow through at least a portion of the system. It should be understood that in some embodiments, the water mentioned elsewhere herein (e.g., deionized (DI) water) may have a resistivity corresponding to any of the ranges described above. Gases may flow through the system, in some cases, together with the solution, for example, as a two-phase solution.

[0168] According to some embodiments, a two-phase solution comprising a solution and a gas can flow through the system (e.g., at least on the cathode side of the system). Advantageously, using a two-phase solution during system cleaning and / or shutdown reduces damage to the system (e.g., to the cathode of the system) compared to flowing only a liquid. In some embodiments, the gas flowing through the system (e.g., as part of the two-phase solution) is inert. For example, the gas may contain N2 and / or Ar. In some embodiments, the gas contains O2 and / or H2. Other gases and / or gas combinations are also possible. In some embodiments, it is desirable for the gas to contain very little or no CO2, as CO2 can form an alkaline solution and cause precipitate formation when the two-phase solution flows. In some embodiments, the gas contains no CO2 or contains CO2 in amounts less than or equal to 5% by weight, less than or equal to 4% by weight, 3% by weight, less than or equal to 2% by weight, less than or equal to 1% by weight, less than or equal to 0.1% by weight, less than or equal to 0.01% by weight, less than or equal to 0.001% by weight, less than or equal to 0.0001% by weight, or less.

[0169] In some embodiments, the liquid is allowed to flow through the electrochemical system before and / or after reducing the absolute value of the applied current density at any suitable flow rate. For example, the liquid may be allowed to flow through the system during system shutdown and / or cleaning. In some cases, the liquid flow rate may depend on the volume of the system. In some embodiments, the liquid may flow through the system at rates greater than or equal to 0.2 mL / min, greater than or equal to 0.5 mL / min, greater than or equal to 1 mL / min, greater than or equal to 2 mL / min, greater than or equal to 5 mL / min, greater than or equal to 30 mL / min, greater than or equal to 50 mL / min, greater than or equal to 100 mL / min, greater than or equal to 500 mL / min, greater than or equal to 1,000 mL / min, or greater than or equal to 2,500 mL / min. In some cases, the liquid can flow through the system at rates less than or equal to 5,000 mL / min, less than or equal to 2,500 mL / min, less than or equal to 1,000 mL / min, less than or equal to 500 mL / min, less than or equal to 100 mL / min, less than or equal to 50 mL / min, less than or equal to 30 mL / min, less than or equal to 5 mL / min, less than or equal to 2 mL / min, less than or equal to 1 mL / min, or less than or equal to 0.5 mL / min. Combinations of the above ranges are possible. Other ranges are also possible. The flow rates here are based on per individual cell meter (e.g., per single electrochemical cell in an electrode stack).

[0170] In some embodiments, gas is flowed through the electrochemical system at various suitable flow rates before and / or after the absolute value of the applied current density is reduced. For example, gas flow may be made through the system during system shutdown and / or cleaning. In some cases, the gas mass flow rate may depend on the system volume. In some embodiments, gas may flow through the system at a mass flow rate greater than or equal to 0.2 standard liters per minute (slpm), greater than or equal to 1 slpm, greater than or equal to 1 slpm, greater than or equal to 5 slpm, greater than or equal to 10 slpm, greater than or equal to 25 slpm, or greater than or equal to 35 slpm. In some cases, liquid may flow at a flow rate less than or equal to 50 slpm, less than or equal to 35 slpm, less than or equal to 25 slpm, less than or equal to 10 slpm, less than or equal to 5 slpm, less than or equal to 1 slpm, or less than or equal to 0.5 slpm. Combinations of the above ranges are possible. Other ranges are also possible. The flow rate here is based on a per-cell meter (e.g., each single electrochemical cell in an electrode stack).

[0171] In some embodiments, after flowing through the solution, a gas can be allowed to flow through the system to remove liquid from the electrode stack and / or maintain the hydrophobicity of the electrodes in the system. Therefore, the gas may contain O2, N2, H2, Ar, etc. Other gases and / or combinations of gases are also possible. Similar to the gases used in two-phase solutions, it may be desirable for the gas flowing through the system to purge to contain very little or no CO2 to avoid precipitation of compounds in the system. For example, the gas may be CO2-free or contain less than or equal to 5% by weight, less than or equal to 4% by weight, 3% by weight, less than or equal to 2% by weight, less than or equal to 1% by weight, less than or equal to 0.1% by weight, less than or equal to 0.01% by weight, less than or equal to 0.001% by weight, less than or equal to 0.0001% by weight, or less CO2.

[0172] In some embodiments, the electrodes, systems, and methods described herein generally relate to improving the efficiency of certain electrochemical reactions within the system and / or the lifetime of such systems. In some embodiments, the system can electrogenerate hydrogen peroxide with relatively high efficiency, having a low overpotential, and the electrolyte solution contains about 0.001 M, 0.01 M, 0.1 M, 0.5 M, 1 M, or 1.5 M and / or less than 2 M, 3 M, 4 M, or 4.8 M NaOH. In some embodiments, the system can electrogenerate hydrogen peroxide with relatively high efficiency, having a low overpotential, and the electrolyte solution contains about 0.001 M, 0.01 M, 0.1 M, 0.5 M, or 1 M and / or less than 1.2 M, 1.4 M, 1.6 M, 1.8 M, or 2 M H₂O₂. The system can be configured to electrochemically generate hydrogen peroxide at the current density described elsewhere herein when the system has an average temperature greater than or equal to 25°C, greater than or equal to 40°C, greater than or equal to 35°C, greater than or equal to 40°C, greater than or equal to 50°C, greater than or equal to 60°C, or greater than or equal to 70°C and / or less than or equal to 80°C, less than or equal to 90°C, or less than or equal to 100°C for at least 1,000 hours, at least 10,000 hours, or at least 30,000 hours. For example, in some cases, the system can electrochemically generate hydrogen peroxide with relatively high efficiency, having a small overpotential, and with an electrolyte solution containing about 2 M NaOH and 1 M hydrogen peroxide sustained at 35°C for at least 1,000 hours, at least 10,000 hours, or at least 30,000 hours. In some such embodiments, the system can operate for no more than 50,000 hours, no more than 30,000 hours, or no more than 10,000 hours. In some cases, due to certain aspects of the electrode structure and / or system described elsewhere herein, some systems can operate at relatively high efficiency (e.g., at least 90% Faraday efficiency, at least 95% Faraday efficiency, or similar for the target compound) and with extremely small overpotentials (e.g., not exceeding 1,000 mV, not exceeding 500 mV, not exceeding 200 mV, not exceeding 100 mV, or similar) for at least 1000 hours, at least 1,000 hours, or at least 10,000 hours. In some cases, the system can operate at such efficiency for no more than 50,000 hours, no more than 10,000 hours, or no more than 1,000 hours. In some cases, the long-term performance can be estimated by operating the relevant system at a relatively high density of applied current or absolute value of voltage relative to parameters sufficient to electrogenerate the desired compound.

[0173] Some aspects involve treating electrochemical systems, such as treating electrodes within an electrochemical system. In some embodiments, treating an electrochemical system includes exposing at least a portion of the electrodes of the electrochemical system to a treatment solution.

[0174] The treatment solution may contain a reducing agent and / or a chelating agent. In some embodiments, the treatment solution contains a reducing agent. In some embodiments, the treatment solution contains a chelating agent. It has been observed that certain cells and / or electrodes in electrochemical systems and / or systems may lose current efficiency after prolonged use (e.g., flooding due to increased hydrophilicity, e.g., from electrode surface oxidation). Surprisingly, it has been observed that certain treatment solutions (e.g., containing chelating agents and / or reducing agents) are able to recover at least some of the lost current efficiency.

[0175] In some embodiments, the treated electrochemical system (or electrodes within it) operates at a current density greater than or equal to 20 mA / cm². 2 (e.g., greater than or equal to 50 mA / cm) 2 ≥100 mA / cm 2 ≥150 mA / cm 2 ≥200 mA / cm 2 ≥300 mA / cm 2 And / or up to 1 A / cm 2 Up to 2 A / cm 2 Up to 3 A / cm 2 Up to 5 A / cm 2 The treatment is performed only after the system has been running for at least 100 hours (e.g., at least 1,000 hours, at least 2,000 hours, at least 5,000 hours, at least 10,000 hours, at least 12,500 hours, or longer) at a speed of 100 hours or more. According to some embodiments, the treated electrode is the cathode of the system. According to such embodiments, the treated cathode may comprise any electrode structure described elsewhere herein. For example, the cathode may comprise a carbon-containing material, such as a nonwoven carbon substrate.

[0176] In some embodiments, exposing at least a portion of the electrode to the treatment solution includes allowing the solution to flow over and / or through at least a portion of the electrode. This flow over and / or through at least a portion of the electrode can be performed at any suitable flow rate described elsewhere herein.

[0177] In some embodiments, the operation of the electrochemical system depends on the type of electrochemical system. In some embodiments, the electrochemical system comprising treated electrodes is configured to electrochemically generate the target substance. While aspects of this application are generally directed to systems configured to electrochemically generate the target substance (e.g., H₂O₂), the electrodes and methods described herein can also be used in other electrochemical systems. For example, other electrochemical systems (to which the aforementioned treatment with the treatment liquid can have beneficial effects (e.g., removal of impurities and / or surface oxidation that may lead to flooding and / or result in high overpotential, low current efficiency, or both; such that the treatment causes at least a partially recovered current efficiency and / or a partially recovered low overpotential)) include, but are not limited to, fuel cells and air batteries. In some embodiments, the electrochemical system is a fuel cell. In some embodiments, the electrochemical system is an air battery. Other electrochemical systems are also possible. For example, other electrochemical systems utilizing reactions believed to occur at a three-phase interface may benefit from the electrode structures and methods described herein. In some embodiments, the operation of an electrochemical system comprising electrodes treated with a treatment liquid involves the electrochemical generation of the desired compound (e.g., H₂O₂). In some implementations, the operation of the electrochemical system includes using the electrochemical system to generate energy (e.g., converting energy from chemical energy to electrical energy).

[0178] In some embodiments, treating the electrochemical system includes exposing at least a portion of the electrodes of the electrochemical system to a treatment solution containing a reducing agent. The reducing agent may contain any reducing agent described elsewhere herein. For example, in some cases, the reducing agent contains sodium bisulfite. It is believed that, in some embodiments, exposing at least a portion of the electrode to the reducing agent can remove at least some of the substances that increase the hydrophilicity of the electrode from at least a portion of the electrode surface. For example, in some embodiments, it is believed that the reducing agent can reduce surface oxidation of the electrode, thereby reducing the hydrophilicity of the electrode surface.

[0179] In some embodiments, treating the electrochemical system includes exposing at least a portion of the electrodes of the electrochemical system to a treatment solution containing a chelating agent. In some embodiments, the chelating agent may contain any chelating agent described elsewhere herein. For example, in some cases, the chelating agent contains EDTA. It is believed that, in some embodiments, exposing at least a portion of the electrodes to the chelating agent can remove at least a portion of substances (e.g., contaminants, precipitates, etc.) from at least a portion of the electrode surface and / or from the electrochemical system that reduce the current efficiency of the electrochemical system during operation by promoting side reactions and / or the decomposition of desired electrogenerated products (e.g., H₂O₂).

[0180] In some embodiments, the method of treating the electrode may further include flowing water over and / or through at least a portion of the electrode. In some embodiments, the water flowing over and / or through at least a portion of the electrode is deionized (DI) water. In some cases, a gas may also flow through the electrochemical system simultaneously with the flow of water (e.g., DI water). In some embodiments, as described elsewhere herein, water (e.g., DI water) and gas are flowed through the electrode in a two-phase solution for a duration of 1 minute or more, 5 minutes or more, etc. Any suitable gas described elsewhere herein may be used. It should be understood that the flow rates of the DI water and / or gas may be selected from the range described elsewhere herein.

[0181] In some embodiments, the electrochemical system may initially operate at a certain initial current efficiency (e.g., Faraday efficiency for electrogenerating the desired product). In some embodiments, the current efficiency of the electrochemical system may decrease after operating for at least 100 hours, at least 1,000 hours, etc. Therefore, in some such embodiments, treating the electrochemical system (e.g., by exposing at least a portion of the electrode (e.g., the cathode) to a treatment solution containing a chelating agent and / or a reducing agent) is expected to restore the current efficiency of the electrochemical system to at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or up to 100% of the initial current efficiency. This can advantageously increase the lifespan of the electrochemical system.

[0182] The embodiments of the technology described herein can be implemented in any of a variety of ways. For example, the embodiments can be implemented using hardware, software, or a combination thereof. When implemented in software, the software code can execute on any suitable processor or set of processors, whether these processors are provided in a single computing device or distributed across multiple computing devices. Such processors can be implemented as integrated circuits, having one or more processors within an integrated circuit assembly, including commercially available integrated circuit assemblies known in the art as CPU chips, GPU chips, microprocessors, microcontrollers, or coprocessors. Alternatively, the processor can be implemented in custom circuitry (e.g., ASICs) or in semi-custom circuitry generated by configuring programmable logic devices. As yet another alternative, the processor can be part of a larger circuit or semiconductor device, whether that device is commercially available, semi-custom, or custom. As a specific example, some commercially available microprocessors have multiple cores, such that one or a subset of these cores can constitute a processor. However, the processor can be implemented using circuitry of any suitable format.

[0183] Furthermore, it should be understood that a computing device including one or more processors can take the form of any of a variety of devices, such as rack-mount computers, desktop computers, laptop computers, or tablet computers. Additionally, computing devices can be embedded in devices that are not typically considered computing devices but have appropriate processing capabilities, including personal digital assistants (PDAs), smartphones, tablets, or any other suitable portable or fixed electronic devices.

[0184] In addition, a computing device may have one or more input and output devices. These devices can be used for purposes such as presenting a user interface. Examples of output devices that can be used to provide a user interface include a display screen for visual output presentation and a speaker or other sound-generating device for audible output presentation. Examples of input devices that can be used for a user interface include a keyboard, individual buttons, and pointing devices such as a mouse, touchpad, and digitizer. As another example, a computing device may receive input information via voice recognition or in other audible formats.

[0185] Such computing devices can be interconnected in any suitable form via one or more networks, including as local area networks (LANs) or wide area networks (WANs), such as corporate networks or the Internet. Such networks can be based on any suitable technology and operate according to any suitable protocol, and can include wireless networks, wired networks, or fiber optic networks.

[0186] Furthermore, the various methods or processes outlined in this paper can be encoded as software that can be executed on one or more processors employing any of a variety of operating systems or platforms. Additionally, such software can be written using any of a variety of suitable programming languages ​​and / or programming or scripting tools, and can also be compiled into machine language code or intermediate code that executes on a framework or virtual machine.

[0187] In this regard, the embodiments described herein can be embodied in a computer-readable storage medium (or multiple computer-readable media) (e.g., computer memory, one or more floppy disks, optical disks (CDs), optical discs, digital video optical discs (DVDs), magnetic tape, flash memory, RAM, ROM, EEPROM, field-programmable gate arrays or other semiconductor devices, or other tangible computer storage media) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods implementing the various embodiments described above. As illustrated in the foregoing examples, a computer-readable storage medium can retain information for a sufficiently long time to provide computer-executable instructions in a non-transitory form. Such a computer-readable storage medium can be removable, such that a program stored thereon can be loaded onto one or more different computing devices or other processors to implement the various aspects of this disclosure as described above. As used herein, the term "computer-readable storage medium" covers only non-transitory computer-readable media that can be considered an article of manufacture (i.e., an article of manufacture) or a machine. Alternatively or additionally, this disclosure can be embodied in computer-readable media other than computer-readable storage media, such as propagating signals.

[0188] The terms “program” or “software” are used in a general sense to refer to any type of computer code or set of computer-executable instructions that can be used to program a computing device or other processor to implement the various aspects of this disclosure as described above. Furthermore, it should be understood that, according to one aspect of this embodiment, one or more computer programs implementing the methods of this disclosure need not reside on a single computing device or processor when executed, but can be distributed in a modular manner across multiple different computers or processors to implement the various aspects of this disclosure.

[0189] Computer-executable instructions can take many forms, such as program modules that are executed by one or more computers or other devices. Typically, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In various implementation schemes, the functionality of program modules can be combined or distributed as needed.

[0190] The implementation described herein can be embodied as a method, of which an example has been provided. The actions performed as part of this method can be ordered in any suitable manner. Therefore, implementations can be constructed in which actions are performed in a different order than those shown, and these implementations may include performing some actions simultaneously, even if they are shown as sequential actions in the exemplary implementation.

[0191] Furthermore, some actions are described as being performed by a “user.” It should be understood that a “user” does not necessarily have to be a single individual, and in some implementations, actions attributable to a “user” may be performed by a group of individuals and / or by individuals in combination with computer-aided tools or other mechanisms.

[0192] In some implementations, the determination and / or monitoring of system parameters (e.g., flow rate, temperature, compound concentration, etc.) can be performed in real time and can be used to provide real-time feedback to adjust one or more parameters of the system (e.g., flow rate, density of applied current, voltage, etc.). Such methods can be implemented in some cases by one or more controllers, for example, including at least one processor operatively coupled to various controllable parts of the system as disclosed herein. The method can be embodied as computer-readable instructions stored on a non-transitory computer-readable memory associated with at least one processor, such that, when executed by at least one processor of the system, any action related to the method disclosed herein can be performed. Furthermore, it should be understood that the sequence of steps disclosed above is exemplary, and the disclosed steps can be performed in a different order, simultaneously, and / or may include one or more additional intermediate steps not shown, as this disclosure is not limited thereto.

[0193] The following examples are intended to illustrate certain embodiments of the present invention, but are not intended to represent the full scope of the invention.

[0194] Example 1

[0195] The following examples describe an electrochemical system for generating hydrogen peroxide.

[0196] The cathode block is made of resin-impregnated graphite. An inlet channel is configured to deliver premixed oxygen and an aqueous solution (e.g., a two-phase solution) from an external source to the cathode electrode, which comprises a nonwoven carbon substrate pretreated with hydrophobic particles and a catalyst layer. An outlet channel is connected to the cathode block and is typically parallel to the inlet channel.

[0197] The anode block is constructed from a nickel block and an anode electrode containing an expanded nickel metal mesh. The inlet channel is configured to deliver electrolyte from an external source to the anode. The outlet channel is connected to the anode and is typically parallel to the inlet channel.

[0198] The anode and cathode blocks are arranged in parallel, and the anode and cathode are separated by a cation exchange membrane (e.g., Nafion) to allow sodium ion conduction.

[0199] A mixture of aqueous electrolyte and oxygen is fed to the cathode block through an inlet channel, flows through the porous cathode, and then exits the cathode block through an outlet channel. An aqueous electrolyte is fed to the anode block through an inlet channel, passes through the anode, and exits the anode block through an outlet channel. Flow rates in the cathode and anode blocks are independently controlled by a mass flow controller and / or a peristaltic pump. The electrolyte flows through the anode block while the electrolyte / oxygen mixture flows through the cathode block, and a voltage of 1.0–1.4 V is applied. Table 1 shows that the amount of hydrogen peroxide generated by the system is 0.2 wt%–0.3 wt% of the electrolyte-oxygen mixture per pass through the cathode, with an efficiency of approximately 98%.

[0200] Table 1: Operating parameters of the system used to generate hydrogen peroxide.

[0201] quantity value <![CDATA[j (A / cm 2 )]]> 0.15-0.4 V 1.0-1.5 Faraday efficiency (%) Approximately 98 <![CDATA[H2O2 (wt%)]]> 0.005% - 0.5% by weight per cycle (e.g., and up to 5% by weight during recycling). NaOH (wt%) 2.1:1 – 3:1 ratio, 2-7 M anode <![CDATA[O2 (stoichiometric ratio with H2O2, x) in the cathode block]]> 2x-10x P (atm) 0.5-3 <![CDATA[Electrode area (cm 2 )]]> 100-500 diaphragm PFSA membrane catalyst Carbon and polytetrafluoroethylene electrode Carbon paper / carbon cloth / carbon felt Flow field Forced convection

[0202] Example 2

[0203] The following examples describe the pretreatment of the electrodes.

[0204] The electrodes are pretreated with PTFE particles suspended in alcohol (e.g., isopropanol, IPA) or water containing surfactants. Figure 9A Images of the electrodes obtained after pretreatment. The left image shows the result of the IPA-pretreated electrode, while the right image shows the water-pretreated electrode. With IPA as the solvent, these electrodes exhibit a relatively uniform PTFE coating (e.g., after IPA evaporation) compared to electrodes prepared using a mixture of water and surfactants as the solvent. Figure 9B show Figure 9A Alternate cross-sectional images of the electrodes shown. The electrode on the left, treated with IPA, exhibits a more uniform PTFE particle distribution than the water-treated electrode on the right, which shows PTFE aggregation on one side of the electrode. The results indicate that pretreatment of the electrode with an IPA solution results in a relatively uniform PTFE distribution on the substrate compared to pretreatment with a solution of water and surfactant.

[0205] Example 3

[0206] The following examples describe the construction and operation of an electrochemical system.

[0207] like Figure 1As shown, an electrochemical system 1 is constructed using the following method. First, an electrochemical cell is constructed, each cell comprising an anode plate, a cathode plate, and a separator. These electrochemical cells are arranged sequentially to form a stack S1. The stack is clamped with a compression plate. An anolyte inlet A7 and an anolyte outlet A8 are provided, connected to the anode plate and fluidly connected to the anode of each cell cell via a common manifold and / or a manifold. A cathode liquid inlet C3 (e.g., for liquid) and a cathode gas inlet O2 and outlet C4 are provided, connected to the cathode plate and fluidly connected to the cathode of each cell cell via a common manifold and / or a manifold.

[0208] Anode electrolyte storage tank A4 is connected to anode electrolyte inlet A7 using anode electrolyte pump A5. Cathode electrolyte storage tank C5 is connected to cathode electrolyte inlet C3 using cathode electrolyte pump C2. Product gas and / or excess reactant gas are captured in collection tank O8 through anode exhaust port O4 and cathode exhaust port O3, and then recirculated to the cathode by liquid ring compressor O5. The flow rates of cathode electrolyte, anode electrolyte, reactant gas, and product gas are metered and regulated by a flow control device (not shown).

[0209] An electric current is applied while the anolyte, catholyte, and reactant gas flow through the electrode stack to electrogenerate compounds.

[0210] Example 4

[0211] The following examples describe electrodes with different substrates, each used to generate hydrogen peroxide. Each electrode is assembled into an electrochemical cell comprising a target cathode electrode, a separator, and a porous metal anode.

[0212] Two electrodes were used for peroxide generation: one containing a substrate of carbon cloth, and the second containing a substrate of carbon felt (e.g., nonwoven fiber). Each electrode was pretreated with PTFE powder suspended in IPA, and then a slurry containing PTFE powder, a PTFE dispersion as a binder, and a carbon-containing active material was applied to the electrode. The electrode was sintered prior to the experiment. The electrolytes used in each experiment were similar to those used in Table 1. Results are as follows: Figure 10 As shown, carbon cloth 902 achieves a maximum current of 24 A at a battery voltage of 1.6 V. Carbon felt can achieve 30 A at a battery voltage of less than or equal to 1.4 V. This indicates that using a substrate containing carbon felt can generate peroxides more efficiently than using a carbon cloth substrate.

[0213] Example 5

[0214] The following examples describe electrodes heated under different conditions during the manufacturing process, wherein each electrode is used to form hydrogen peroxide.

[0215] Six electrodes were used for peroxide generation, each heated under different conditions. The electrodes were prepared in the same manner as in Example 4 and then used for peroxide generation. The results are as follows: Figure 11A-11B As shown.

[0216] The first set of four electrodes was sintered in nitrogen at different temperatures. The voltage required to maintain the applied current is as follows: Figure 11A As shown, the voltage is inversely proportional to the sintering temperature. For example, electrode 916, with the highest sintering temperature at 400°C, produces the lowest operating voltage. Electrode 910, with the lowest sintering temperature of 300°C, cannot maintain the applied current. Electrode 916, sintered at 400°C, also exhibits the longest service life.

[0217] The second set of two electrodes were sintered at similar temperatures in different atmospheres. The voltage required to maintain the applied current is shown in [figure missing]. Figure 11B In the oxidizing atmosphere, electrode 918 requires a lower voltage. However, the voltage increases rapidly and the electrode's Faraday efficiency begins to decline after 500 hours. Electrode 920, sintered in an inert atmosphere, can persist for 2,000 hours before showing signs of declining Faraday efficiency. Sintering in an oxidizing atmosphere increases the hydrophilicity of the carbon-containing active material. Initially, this provides a higher reaction surface area. However, it quickly begins to flood, disrupting oxygen transport to the catalytic site and ultimately leading to failure.

[0218] Example 6

[0219] The following examples describe electrodes with different compositions of slurry containing PTFE and active materials, wherein each electrode is used to form hydrogen peroxide.

[0220] Three electrodes for peroxide generation were prepared, each using a different PTFE particle source in a slurry containing active material. These electrodes were prepared as described in Example 4 and then used for peroxide generation. A maintenance voltage of 300 mA / cm² was maintained. 2 The voltage required for a current density of 50 hours (e.g., PTFE powder only, and PTFE powder and binder) or 500 hours (e.g., PTFE binder only), and the voltage subsequently maintained at 400 mA / cm on each electrode. 2 The voltage required for current density is as follows Figure 12 As shown. Electrode 922 was prepared using only a binder, electrode 924 was prepared using only PTFE powder, and electrode 926 was prepared using both PTFE powder and a binder. Throughout the experiment, electrode 926 was maintained at 400 mA / cm². 2 The electrode 926 has the lowest voltage required to maintain the applied current density, indicating higher electrocatalytic efficiency compared to other electrodes. The voltage rise rate of electrode 926 is also the slowest.

[0221] Example 7

[0222] The following examples describe electrodes with different amounts of PTFE in the catalyst layer, wherein each electrode is used to form hydrogen peroxide.

[0223] Three electrodes were prepared for peroxide generation, each using a different amount of PTFE powder in a slurry containing active material and PTFE particles. The pretreatment of the three electrodes was identical. The electrodes were prepared in the same manner as in Example 4 and then used for peroxide generation. A voltage of 300 mA / cm² was maintained on each electrode. 2 and 400 mA / cm 2 The voltage required for current density is as follows Figure 13 As shown. It has 0.6 mg / cm³. 2 The electrode of PTFE 934 has a lower content of PTFE powder than 932 (0.3 mg / cm³). 2 ) and contains a relatively high amount of PTFE powder 930 (1.9 mg / cm³). 2 The electrode exhibits higher efficiency. This indicates that the amount of PTFE present in the electrode affects catalysis, and that too much or too little PTFE (e.g., or other hydrophobic polymers) may reduce catalytic efficiency.

[0224] Example 8

[0225] The following examples describe electrodes with different amounts of active material, wherein each electrode is used to form hydrogen peroxide.

[0226] Two electrodes for hydrogen peroxide generation were prepared, each using a different amount of active material coated onto a pretreated electrode. The electrodes were prepared in the same manner as in Example 4 and then used for peroxide generation. A voltage of 300 mA / cm² was maintained on each electrode. 2 The voltage required for the current density is shown in FIG14. The total active material concentration is 3.4 mg / cm³. 2 The electrode 942 (containing carbon, PTFE binder, and PTFE powder) has a total active material content of 0.85 mg / cm³. 2 Electrode 940 exhibits higher efficiency. This indicates that the amount of active material present in the electrode affects the catalytic activity, and insufficient loading may reduce catalytic efficiency.

[0227] Example 9

[0228] The following examples describe electrodes with different amounts of hydrophobic particles pretreated on a substrate, wherein each electrode is used to form hydrogen peroxide.

[0229] Three electrodes for hydrogen peroxide generation were prepared, each with a different amount of hydrophobic particles coated on a pretreated electrode. The electrodes were prepared in the same manner as in Example 4 and then used for peroxide generation. An electrode 904 was formed with 3 mg / cm² particles on the top and bottom planes of the substrate. 2 Hydrophobic particles with a moderate loading. Another electrode 950 is formed, which is located on the top and bottom planes of the substrate at a loading of 2 mg / cm². 2 Hydrophobic particles with low loading are used to form the third electrode 952, which has a loading of 4.5 mg / cm² only on a single plane opposite the substrate and the plane forming the active material. 2 Maintain 300 mA / cm on each electrode. 2 The voltage required for current density is as follows Figures 15A-15B As shown. There is 3.0 mg / cm² on both sides. 2 The 904 electrode with hydrophobic particles has a 2.0 mg / cm² difference compared to the two sides. 2 Electrodes with hydrophobic particles exhibited higher efficiency. Electrode 952, which underwent pretreatment on only one of the two planes of the substrate, performed worse than electrodes 904 and 952, with the voltage increasing before 750 hours of operation. This indicates that the amount of hydrophobic particles present in the electrode pretreatment affects catalysis, and insufficient loading may reduce catalytic efficiency. Furthermore, this suggests that particles may need to be present on both sides of the substrate. In other words, it is insufficient to include hydrophobic particles only in the active material forming the catalyst layer.

[0230] Example 10

[0231] The following examples describe exemplary electrodes 904 and 960 that demonstrate long lifespan, wherein each electrode is used to form hydrogen peroxide.

[0232] The active material loading in electrode 960 is approximately twice that of electrode 904, and the pretreatment process involves 50% more hydrophobic particles. Maintaining 300 mA / cm² 2 The voltage required for the operating current is as follows Figure 16 As shown. The voltage of electrodes 904 and 960 remained below 1.5 V for more than 10,000 hours, and the Faraday efficiency of hydrogen peroxide production remained above 95%.

[0233] Example 11

[0234] The following examples describe exemplary electrodes.

[0235] The electrode was prepared as described in Example 10 and operated within the current density range used to generate hydrogen peroxide. Figure 17 The experimental results are presented. During the electrochemical generation of hydrogen peroxide, the voltage required for each applied current density is among the lowest values ​​reported in the literature.

[0236] Example 12

[0237] The following examples describe a method for treating an electrochemical system.

[0238] Electrodes in electrochemical systems can be fabricated to possess specific hydrophobicities (or hydrophilicities) desirable for certain applications. However, during operation of the electrochemical system, surface functional groups (e.g., oxygen) may form on certain surfaces of the electrodes. This is particularly relevant in the case of carbon electrodes. The introduction of such surface functional groups can alter the hydrophobicity (hydrophilicity) of the electrode from its initial fabrication state, which can adversely affect electrochemical performance. For example, in some embodiments, increased electrode hydrophilicity may lead to higher overpotentials and / or undesirable side reactions manifested as reduced current efficiency for the desired product. Additionally, feedstocks to the electrochemical system (e.g., water, treated water, and / or electrolyte solutions) may occasionally or continuously contain contaminants that can further alter the electrode's hydrophobicity (e.g., by altering hydrophobicity or otherwise) and / or cause undesirable side reactions (e.g., by catalytic decomposition of electrochemically generated compounds of interest). Such contaminants can be difficult to trace.

[0239] In this embodiment, an electrochemical cell (according to an embodiment of this disclosure) comprising a nonwoven carbon substrate cathode is operated to generate hydrogen peroxide for approximately 18,000 hours. Figure 18 The graphs show the changes in battery voltage and current efficiency over time. During the first 12,500 hours of operation, the battery efficiency was 3 kA / m. 2 It operates at current densities with voltage varying between 1.2 and 1.5 V. The current efficiency generated by the peroxide is approximately 95%–100%.

[0240] After approximately 12,500 hours of operation, an unknown contaminant in the water entering the cathode caused the current efficiency to drop to as low as approximately 20%. The battery was shut down following the procedure described elsewhere in this document. A treatment solution containing an aqueous solution of ethylenediaminetetraacetic acid (EDTA) was prepared using deionized water, and this solution was circulated through the cathode electrode while oxygen also flowed through it in a two-phase solution. The cathode electrode was then rinsed with deionized water for 5 minutes while oxygen continued to flow. The battery was restarted, and the current efficiency temporarily recovered to approximately 50%. The procedure was repeated several times, and the battery eventually reached a current efficiency of 95%. However, during the next 2,000 hours of operation, the current efficiency subsequently dropped below 80%. The loss of current efficiency was attributed to the unknown contaminant promoting side reactions and / or the decomposition of hydrogen peroxide, and it was believed that EDTA chelated the unknown contaminant and removed it from the system, resulting in a temporary recovery of the current efficiency to 95%. The subsequent drop in current efficiency to 80% was attributed to electrode flooding.

[0241] The current density was reduced to 1.5 kA / m. 2 The current efficiency increased to approximately 85%. This improvement in current efficiency at lower operating current densities was expected due to the lower overpotential, which drives fewer side reactions. However, the efficiency did not improve further, and the cell shut down again. A 0.3% sodium bisulfite aqueous solution was prepared using deionized water and circulated through the cathode electrode while oxygen also flowed through it. Washing was performed for 60 minutes. Then, the cathode electrode was rinsed with deionized water for 5 minutes while oxygen continued to flow. The cell was then operated at 1.5 kA / m 2 The current density was restarted. The current efficiency increased to approximately 95%. After approximately 100 hours, the current density increased to 3 kA / m. 2 The current efficiency subsequently stabilized at approximately 95%. The additional recovery of current efficiency to 95% is attributed to the removal of surface oxidation by the reducing agent (sodium bisulfite). Surface oxidation is believed to cause the electrode surface to become flooded, thereby reducing the current efficiency of the oxygen reduction reaction to generate hydrogen peroxide. Furthermore, the reducing agent is believed to also contribute to the removal of contaminants.

[0242] While several embodiments of the invention have been described and illustrated herein, those skilled in the art will readily conceive of a variety of other means and / or structures for implementing the functions described herein and / or obtaining the results and / or one or more advantages described herein, and each of such variations and / or modifications is considered to be within the scope of the invention. More generally, those skilled in the art will readily understand that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and actual parameters, dimensions, materials, and / or configurations will depend on the specific application to which the teachings of the invention are applied. Those skilled in the art will recognize or be able to determine many equivalent embodiments of the specific embodiments of the invention described herein through experiments not exceeding conventional methods. Therefore, it should be understood that the foregoing embodiments are presented by way of example only, and that the invention may be practiced in ways other than those specifically described and claimed within the scope of the appended claims and their equivalents. The invention is directed toward each individual feature, system, article, material, and / or method described herein. Furthermore, any combination of two or more of these features, systems, articles, materials, and / or methods is also included within the scope of the invention if they do not contradict each other.

[0243] The articles “a” and “an” used in the specification and claims herein, unless the opposite is explicitly stated, shall be understood to mean “at least one (agent)”.

[0244] The phrase “and / or” as used herein in the specification and claims should be understood to mean “any one or both” of the elements so connected, that is, elements that coexist in some cases and exist separately in others. Other elements may optionally be present, whether or not they are related to the specifically designated elements, unless expressly stated otherwise. Thus, as a non-limiting example, when used in conjunction with open-ended language such as “comprising”, “A and / or B” may refer to A without B (optionally including elements other than B) in one embodiment; to B without A (optionally including elements other than A) in another embodiment; to both A and B (optionally including other elements) in yet another embodiment; and so on.

[0245] As used in this specification and claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” should be interpreted as inclusive, that is, including multiple elements or at least one of the elements in the list, but also including more than one, as well as optional additional items not listed. Only terms that explicitly indicate the opposite (e.g., “only one of…” or “exact one of…”, or, when used in the claims, “consisting of…”) will refer to multiple elements or exactly one of the elements in the list. In general, as used herein, the term “or” followed by an exclusive term (e.g., “any one of…”, “one of…”, “only one of…”, or “exact one of…”) should be interpreted only as indicating an exclusive alternative (i.e., “one or the other, but not both”). “Substantially consisting of…” when used in the claims should have its ordinary meaning as used in the field of patent law.

[0246] As used in this specification and claims, the phrase "at least one" when referring to a list of one or more elements should be understood to mean at least one element selected from any one or more elements in the list, but not necessarily including at least one of every element specifically listed in the list, and does not exclude any combination of elements in the list. This definition also allows for the optional presence of elements other than those explicitly identified in the list of elements referred to by the phrase "at least one," whether related to or unrelated to those explicitly identified elements. Thus, as a non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B," or equivalently "at least one of A and / or B") can mean, in one embodiment, at least one (optionally including more than one) A, with no B (and optionally including elements other than B); in another embodiment, at least one (optionally including more than one) B, with no A (and optionally including elements other than A); in yet another embodiment, at least one (optionally including more than one) A and at least one (optionally including more than one) B (and optionally including other elements); and so on.

[0247] As used in this article, “weight%” is an abbreviation for weight percentage.

[0248] Some implementation schemes may be embodied as methods, of which various examples have been described. Actions performed as part of a method may be ordered in any suitable manner. Thus, implementation schemes may be constructed in which actions are performed in a different order than those shown, and these implementation schemes may include actions different from those described (e.g., more or fewer), and / or may involve performing some actions simultaneously, even though these actions are shown to be performed sequentially in the implementation schemes specifically described above.

[0249] The use of ordinal terms (such as "first", "second", "third" etc.) to modify claim elements does not indicate any priority, order, or sequence of one claim element relative to another, nor does it indicate the chronological order of the method actions. Rather, it serves only as a label to distinguish one claim element with a certain name from another element with the same name (but without ordinal terms).

[0250] In the claims and the foregoing description, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” etc., shall be understood as open-ended, meaning including but not limited to. Only the transitional phrases “consisting of” and “consisting substantially of” shall be closed or semi-closed transitional phrases as specified in Section 2111.03 of the U.S. Patent Examination Procedure Manual.

Claims

1. An electrode comprising: Nonwoven substrates, which include fibers containing carbon; A first hydrophobic polymer is formed on at least a portion of the nonwoven substrate; and The catalyst layer comprises a second hydrophobic polymer and a carbon-containing active material, said active material having a surface area greater than or equal to 5 μm. 2 / g and less than or equal to 5,000 m 2 / g surface area, and formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer.

2. An electrode comprising: Nonwoven substrates, including carbon-containing fibers; and Multiple hydrophobic regions are distributed on at least a portion of the nonwoven substrate. At least a portion of the plurality of hydrophobic regions is at least partially surrounded by hydrophilic regions.

3. A system comprising the electrode as claimed in claim 1.

4. A system comprising the electrode as claimed in claim 2.

5. The system of claim 3 or 4, wherein the electrode is configured to electrogenerate hydrogen peroxide.

6. The system of claim 5, wherein the system is configured to operate with a Faraday efficiency of greater than or equal to 95% for generating hydrogen peroxide.

7. The electrode of claim 1, wherein the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

8. The electrode of claim 1 or 7, wherein the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

9. The electrode according to any one of claims 1 and 7-8, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises PTFE powder and / or PTFE micropowder.

10. The electrode according to any one of claims 1 and 7-9, wherein the nonwoven substrate has a porosity of at least 0.

85.

11. The electrode according to any one of claims 1 and 7-10, wherein the thickness of the nonwoven substrate is greater than or equal to 0.75 mm.

12. The electrode according to any one of claims 1 and 7-11, wherein the thickness of the nonwoven substrate is greater than or equal to 2 mm.

13. The electrode of any one of claims 11-12, wherein the thickness is the uncompressed thickness.

14. The electrode of any one of claims 1 and 7-13, wherein the nonwoven substrate has an uncompressed thickness, wherein the substrate has a compressed thickness when incorporated into the electrochemical system, and wherein the ratio of the uncompressed thickness to the compressed thickness is greater than or equal to 1.05 and less than or equal to 2.

0.

15. The electrode according to any one of claims 1 and 7-14, wherein the nonwoven substrate comprises elemental carbon.

16. The electrode according to any one of claims 1 and 7-15, wherein the nonwoven substrate comprises carbon felt.

17. The electrode according to any one of claims 1 and 7-16, wherein the nonwoven substrate is carbon felt.

18. The electrode according to any one of claims 8-17, wherein the average maximum cross-sectional size of the PTFE particles does not exceed 25 micrometers.

19. The electrode according to any one of claims 8-18, wherein the PTFE particles form a plurality of hydrophobic regions.

20. The electrode of claim 2, wherein the plurality of hydrophobic regions comprise a hydrophobic polymer.

21. The electrode of claim 2 or 20, wherein the hydrophobic polymer is PTFE.

22. The electrode of any one of claims 2 and 20-21, wherein the hydrophilic region comprises carbon.

23. The electrode of any one of claims 8-22, wherein the PTFE particles permeate at least 5% of the thickness of the nonwoven substrate.

24. The electrode of any one of claims 8-23, wherein the PTFE particles penetrate the entire thickness of the nonwoven substrate.

25. The electrode of any one of claims 1, 7-19, and 23-24, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises PTFE from a dispersion and / or emulsion.

26. The electrode of any one of claims 1, 7-19, and 23-25, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises PTFE powder and / or micropowder and / or a mixture of PTFE from dispersions and / or emulsions.

27. An electrode comprising: Nonwoven substrates, which include fibers containing carbon; A first hydrophobic polymer is formed on at least a portion of the nonwoven substrate; and The catalyst layer comprises a second hydrophobic polymer and a carbon-containing active material. The electrode is configured to contain greater than or equal to 0.001 M and less than or equal to 4.8 M OH. - When configured in a system containing ≥0.001 M and ≤2 M H₂O₂ with an average temperature of at least 35°C, at a voltage of ≤1.5 V at a voltage of ≥300 mA / cm², 2 Electrochemical generation of hydrogen peroxide at a current density lasted for 1,000 hours or more.

28. The electrode of claim 27, wherein the OH - The equilibrium ions are alkali metals.

29. The electrode of claim 27 or 28, wherein the OH - The equilibrium ion is Na. + and / or K + .

30. The electrode according to any one of claims 27-29, wherein OH in the system + The molecular ratio of H2O2 to H2O2 is approximately 2 to 1.

31. A method comprising: Mixing liquids and gases to form a two-phase solution; The two-phase solution flows over and / or through at least a portion of an electrode comprising a substrate including carbon-containing nonwoven fibers; as well as A voltage is applied to the electrode, causing at least a portion of the gas to participate in the reaction to electrochemically generate a compound at the electrode.

32. The method of claim 31, wherein the hydrophobic polymer and / or catalyst layer are located on the substrate.

33. The method of claim 31 or 32, wherein the electrode comprises a core having a depth of 100 cm or greater. 3 In a volumetric electrochemical system, wherein the flow rate of the liquid in the two-phase solution is greater than or equal to 30 mL / min and / or the mass flow rate of the gas in the two-phase solution is greater than or equal to 0.2 slpm.

34. The method of claim 33, wherein the liquid flow rate of the two-phase solution is greater than or equal to 30 mL / min per individual cell meter, and / or the gas mass flow rate of the two-phase solution is greater than or equal to 0.2 slpm per individual cell meter.

35. The method of any one of claims 31-34, wherein the electrodes have a diameter greater than or equal to 1 cm per individual cell. 2 The electrochemically active geometric area, and the liquid flow rate of the two-phase solution is greater than or equal to 30 mL / min per individual cell and / or the gas mass flow rate of the two-phase solution is greater than or equal to 0.2 slpm per individual cell.

36. The method of any one of claims 31-35, wherein the liquid flow rate of the two-phase solution is greater than or equal to 200 mL / min and the gas mass flow rate of the two-phase solution is greater than or equal to 5 slpm.

37. The method of any one of claims 31-36, wherein the liquid flow rate of the two-phase solution is greater than or equal to 200 mL / min per individual cell meter, and / or the gas mass flow rate of the two-phase solution is greater than or equal to 5 slpm per individual cell meter.

38. The method of any one of claims 31-37, wherein the compound is hydrogen peroxide.

39. The method of any one of claims 31-38, wherein the gas comprises oxygen.

40. The method of any one of claims 31-39, wherein the liquid comprises an alkaline hydroxide.

41. The method of any one of claims 31-40, wherein the liquid flows at a rate of at least 5 mL / min.

42. The method of any one of claims 41, wherein the liquid flows at a rate of at least 5 mL / min based on each individual cell.

43. The method of any one of claims 31-42, wherein the gas flows at a mass flow rate of at least 0.5 slpm.

44. The method of claim 43, wherein the gas flows at a mass flow rate of at least 0.5 slpm per individual cell.

45. The method of any one of claims 31-44, wherein the electrode is the cathode in the system.

46. ​​The method of any one of claims 32-45, wherein the hydrophobic polymer is a first hydrophobic polymer and the catalyst layer comprises a second hydrophobic polymer and / or an active material containing carbon, and wherein the catalyst layer is formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer.

47. The method of claim 46, wherein the surface area of ​​the active material is greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g.

48. The method of claim 46 or 47, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises PTFE particles.

49. The method of any one of claims 46-48, wherein the catalyst layer comprises less than or equal to 0.01% by weight of metal.

50. A method comprising: The solution flows over at least a portion of the surface area of ​​the electrodes in the compartment; A compound is electrochemically generated in the solution at the electrode. The solution flows from the electrode through the outlet of the compartment; as well as At least a portion of the solution is recirculated from the outlet of the compartment to the inlet of the compartment, such that the compound is present in the solution in an amount greater than or equal to 0.2% by weight.

51. The method of claim 50, further comprising causing the recirculated solution to flow over and / or through at least a portion of the surface area of ​​the electrode.

52. The method of any one of claims 50 or 51, further comprising removing at least a portion of the solution containing the electrochemically generated compound.

53. The method of any one of claims 50-52, wherein the compound is hydrogen peroxide.

54. The method of any one of claims 50-53, wherein the electrode is part of a system comprising at least one gas manifold and at least one liquid manifold, wherein the at least one gas manifold and at least one liquid manifold supply only to a junction of gas and liquid inlets in the cathode or anode flow plate and / or flow box within the battery.

55. The method of any one of claims 50-54, wherein the electrode comprises a substrate including carbon-containing nonwoven fibers.

56. The method of claim 55, wherein the hydrophobic polymer and / or catalyst layer are located on the substrate.

57. The method of any one of claims 50-56, wherein the electrode is the cathode in the system.

58. The method of claim 56 or 57, wherein the hydrophobic polymer is a first hydrophobic polymer and the catalyst layer comprises a second hydrophobic polymer and / or an active material containing carbon, and wherein the catalyst layer is formed on at least a portion of the nonwoven substrate and / or the first hydrophobic polymer.

59. The method of claim 58, wherein the surface area of ​​the active material is greater than or equal to 5 m². 2 / g and less than or equal to 5,000 m 2 / g.

60. The method of claim 58 or 59, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises PTFE particles.

61. The method of any one of claims 56-60, wherein the catalyst layer comprises less than or equal to 0.01% by weight of metal.

62. A method for modifying an electrode, the method comprising: The electrode is provided, the electrode comprising a nonwoven substrate containing carbon fibers; The electrode is pretreated by applying a first solution containing a liquid having a vapor pressure greater than or equal to 1 kPa and a first hydrophobic polymer to the electrode; as well as A second solution comprising a second hydrophobic polymer and / or PTFE binder and a carbon-containing active material is applied to the electrode.

63. The method of claim 62, wherein the liquid in the first solution comprises an organic solvent.

64. The method of claim 62 or 63, wherein the liquid in the first solution comprises a polar organic solvent.

65. The method of any one of claims 62-64, wherein the liquid in the first solution comprises an alcohol.

66. The method of any one of claims 62-65, wherein the liquid in the first solution comprises isopropanol.

67. The method of any one of claims 62-66, wherein the second solution comprises water.

68. The method of any one of claims 62-67, wherein the second solution comprises a surfactant.

69. The method of any one of claims 62-68, wherein the nonwoven substrate comprises carbon felt.

70. The method of any one of claims 62-69, further comprising heating the electrode.

71. The method of claim 70, wherein heating the electrode is performed in an atmosphere at a temperature greater than or equal to 380°C.

72. The method of claim 70 or 71, wherein heating of the electrode is performed in a non-oxidizing atmosphere.

73. The method of claim 72, wherein the non-oxidizing atmosphere contains less than or equal to 1% by weight of oxygen.

74. The method of any one of claims 70-73, wherein heating of the electrode is performed in an atmosphere containing N2 and / or Ar.

75. The method of any one of claims 62-74, wherein the liquid in the first solution has a vapor pressure of less than or equal to 30 kPa.

76. The method of any one of claims 62-75, wherein the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

77. The method of any one of claims 62-76, wherein the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

78. The method of claim 77, wherein the polytetrafluoroethylene (PTFE) particles of the first hydrophobic polymer and / or the second hydrophobic polymer are derived from PTFE powder and / or micropowder.

79. A method for electrochemically generating a compound, the method comprising: The electrode stack is purged by allowing gas to flow through it. Allow water to flow through the electrode stack; The electrolyte is allowed to flow through the electrode stack for at least 1 minute, while the absolute value of the applied current is less than or equal to 0.1 mA / cm². 2 ; The absolute value of the applied current density is greater than or equal to 15 mA / cm². 2 And less than or equal to 125 mA / cm 2 The amount is increased every 5 minutes until the density of the applied current reaches at least 150 mA / cm². 2 ; A compound is electrochemically generated in the electrode stack and the electrode stack is heated to at least 35°C, while the applied current is maintained at at least 150 mA / cm². 2 ; as well as Increase the absolute value of the applied current to at least 300 mA / cm. 2 .

80. The method of claim 79, wherein the water flowing through the electrode stack is deionized water.

81. The method of claim 79 or 80, wherein the absolute value of the applied current density increases by 30 mA / cm² every 5 minutes. 2 Until the density of the applied current reaches at least 150 mA / cm². 2 .

82. The method of any one of claims 79-81, wherein the compound is hydrogen peroxide.

83. The method of any one of claims 79-82, wherein heating the electrode stack comprises Joule heating.

84. The method of any one of claims 79-83, wherein heating the electrode stack comprises heating the electrolyte solution.

85. The method of claim 84, wherein heating the electrolyte solution comprises Joule heating.

86. The method of any one of claims 79-85, wherein heating the electrolyte solution and / or heating the electrode stack comprises using a resistance heating coil.

87. The method of any one of claims 79-86, wherein heating the electrode stack comprises using a heat exchanger.

88. The method of any one of claims 79-87, wherein the average temperature of the electrolyte solution as it flows into and / or flows through the electrode stack is at least 35°C.

89. The method of any one of claims 79-88, wherein the absolute value of the density of the applied current is less than or equal to 10 mA / cm². 2 / min increase.

90. The method of any one of claims 79-89, wherein the electrochemical generation of the compound occurs at the electrodes in the electrode stack.

91. The method of claim 90, wherein the electrode comprises a substrate including carbon-containing nonwoven fibers.

92. The method of claim 90 or 91, wherein the electrode further comprises a first hydrophobic polymer formed on at least a portion of the substrate.

93. The method of any one of claims 90-92, wherein the electrode further comprises a catalytic layer on at least a portion of the substrate, the catalytic layer comprising a second hydrophobic polymer and / or an active material.

94. The method of claim 92, wherein the first hydrophobic polymer and / or the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

95. The method of claim 93 or 94, wherein the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

96. The method of any one of claims 93-95, wherein the catalyst layer comprises an active material on at least a portion of the substrate, wherein the active material comprises carbon.

97. The method of any one of claims 93-96, wherein the active material comprises less than or equal to 0.01% by weight of a metal.

98. The method of any one of claims 91-97, wherein the substrate comprises carbon felt.

99. A method for shutting down an electrode stack, the method comprising: Compounds are electrochemically generated in the electrode stack; Reduce the absolute value of the current applied to the electrode stack to less than or equal to 0.1 mA / cm. 2 ; The absolute value of the applied current is less than or equal to 0.1 mA / cm. 2 Simultaneously, the liquid flows through the electrode stack for a duration of greater than or equal to 1 minute; and Gas is flowed through the electrode stack to purge liquid from the electrode stack.

100. The method of claim 99, wherein, based on each individual battery, the flow rate of the liquid is greater than or equal to 0.2 mL / min and less than or equal to 5,000 mL / min.

101. The method of claim 99 or 100, wherein, based on a single battery, the mass flow rate of the gas is greater than or equal to 0.2 slpm and less than or equal to 50 slpm.

102. The method of any one of claims 99-101, further comprising flowing water through the electrode stack.

103. The method of claim 102, wherein the water flowing through the electrode stack is deionized water.

104. The method of any one of claims 102-103, wherein the gas and the liquid flow simultaneously through the electrode stack in the form of a two-phase solution.

105. The method of any one of claims 99-104, wherein the gas contains no CO2 or contains less than or equal to 5% by weight of CO2.

106. A method for cleaning an electrode stack, the method comprising: Compounds are electrochemically generated in the electrode stack; Reduce the absolute value of the current applied to the electrode stack to less than or equal to 0.1 mA / cm. 2 ; Precipitates are removed from the electrode stack by allowing a solution containing a reducing agent and / or a chelating agent to flow continuously for less than or equal to 5 minutes. as well as Water is allowed to flow through the electrode stack for a continuous period of 30 minutes or more.

107. The method of claim 106, wherein the water flowing through the electrode stack is deionized water.

108. The method of any one of claims 106-107, wherein the electrode stack is cleaned at least once a year.

109. The method of any one of claims 106-108, further comprising flowing gas through the electrode stack to dry the electrode stack.

110. The method of claim 109, wherein the gas contains no CO2 or contains less than or equal to 5% by weight of CO2.

111. The method of any one of claims 109-110, wherein the gas and the water flow simultaneously through the electrode stack in the form of a two-phase solution.

112. The method of any one of claims 106-111, wherein the electrode stack is cleaned at least once a year for a continuous operation with a lifespan of 10,000 hours or more.

113. The method of any one of claims 106-112, wherein the electrochemical generation of the compound occurs at the electrodes in the electrode stack.

114. The method of claim 113, wherein the electrode comprises a substrate including carbon-containing nonwoven fibers.

115. The method of claim 113 or 114, wherein the electrode further comprises a first hydrophobic polymer formed on at least a portion of the substrate.

116. The method of any one of claims 113-115, wherein the electrode further comprises a catalytic layer on at least a portion of the substrate, the catalytic layer comprising a second hydrophobic polymer and / or an active material.

117. The method of claim 115 or 116, wherein the first hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

118. The method of claim 116 or 117, wherein the second hydrophobic polymer comprises polytetrafluoroethylene (PTFE) particles.

119. The method of any one of claims 116-118, wherein the active material comprises carbon.

120. The method of claim 116, wherein the active material comprises less than or equal to 0.01% by weight of a metal.

121. The method of any one of claims 114-120, wherein the substrate comprises carbon felt.

122. The method of any one of claims 106-121, wherein the reducing agent comprises sodium bisulfite, sodium metabisulfite, and / or sodium sulfite.

123. The method of any one of claims 106-122, wherein the chelating agent comprises citric acid.

124. The method of any one of claims 111-123, wherein the gas is passed through a liquid ring compressor prior to the formation of the two-phase solution.

125. The method of any one of claims 31-49, wherein the gas is passed through a liquid ring compressor before the liquid and the gas are mixed to form a two-phase solution.

126. The system of any one of claims 3-6, wherein the electrode is configured to electrogenerate a compound.

127. The method of any one of claims 62-78, further comprising the step of repeatedly pretreating the electrode.

128. A method for treating an electrochemical system, the method comprising: The value is greater than or equal to 20 mA / cm 2 At least a portion of the electrodes in an electrochemical system operating at a current density of at least 100 hours are exposed to a treatment solution containing a reducing agent and / or a chelating agent.

129. The method of claim 128, wherein during the exposure, the electrochemical system was at a voltage greater than or equal to 20 mA / cm². 2 It can operate at a current density for at least 1,000 hours.

130. The method of claim 128 or 129, further comprising restoring the current efficiency of the electrochemical cell to 70% of the efficiency prior to operation for at least 100 hours.

131. The method of any one of claims 128-130, wherein exposing the at least portion of the electrode to the treatment liquid comprises causing the treatment liquid to flow over and / or through the at least portion of the electrode.

132. The method of any one of claims 128-131, further comprising removing at least a portion of the precipitate from the electrochemical system and / or removing hydrophilic sources and / or contaminants from said at least a portion of the electrode.

133. The method of any one of claims 128-132, further comprising removing at least a portion of the surface oxidation source from said at least a portion of the electrode.

134. The method of any one of claims 128-133, further comprising allowing water and gas to flow simultaneously through the electrochemical system in the form of a two-phase solution for a duration of greater than or equal to 1 minute.

135. The method of claim 134, wherein the water flowing through the electrochemical system is deionized water.

136. The method of any one of claims 128-135, wherein the electrochemical system is an electrolysis system, a fuel cell, and / or an air battery.

137. The method of any one of claims 128-136, wherein the operation of the electrochemical system comprises electrochemically generating a substance.

138. The method of claim 137, wherein the substance is hydrogen peroxide.

139. The method of any one of claims 128-138, wherein operation of the electrochemical system comprises electrochemically generating energy using the electrochemical system.

140. The method of any one of claims 128-139, wherein the electrode is a cathode.

141. The method of claim 140, wherein the cathode comprises an electrode as described in any one of claims 1, 2 or 7-30.

142. The method of any one of claims 128-141, wherein the treatment liquid comprises a reducing agent.

143. The method of claim 142, wherein the reducing agent comprises bisulfite anion, ascorbic acid, oxalic acid and / or thiosulfate anion.

144. The method of any one of claims 128-143, wherein the reducing agent comprises a bisulfite anion.

145. The method of claim 144, wherein the reducing agent comprises sodium bisulfite.

146. The method of any one of claims 128-145, wherein the treatment liquid comprises the chelating agent.

147. The method of any one of claims 128-146, wherein the chelating agent comprises NTA, TPP, citric acid and / or EDTA.

148. The method of any one of claims 128-147, wherein the chelating agent comprises ethylenediaminetetraacetic acid (EDTA).

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