Anion exchange membrane carbon oxide electrolyzers and methods of use

Abstract

Provided are methods for operating an electrolyzer equipped with an anion exchange membrane for carbon oxide reduction while monitoring conductivity of an anolyte solution. Adjustments can be made, or an anolyte restoration operation can be conducted when indicated by an elevated conductivity value or a reduced conductivity value; such as by replacing the anolyte solution with water, lowering the salt concentration of the anolyte solution or by current modulation. A method for activating an electrochemical cell and a method of preparing an electrochemical cell are also provided.

Description

ANION EXCHANGE MEMBRANE CARBON OXIDE ELECTROLYZERS AND METHODS OF USEINCORPORATION BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes.BACKGROUND

[0002] Anion exchange membranes are a well-known type of polymer electrolyte membrane useful for the electrolytic reduction of carbon oxides to produce carbon-containing products. However, during continuous operation the anion exchange membrane electrolyzers can become clogged with salt which can impact the normal performance of an electrochemical cell. An excess of salt or an elevated salt concentration in the electrochemical cell may hinder the desired electrochemical reaction, resulting in either detrimental slowing of the rate of reaction; or even cause complete cessation of functioning of the electrochemical cell. To scale up electrolytic reduction of carbon oxides, it would be desirable to have techniques for preventatively monitoring and addressing accumulation of salt in order to improve the efficiency and / or operational lifespan of an electrochemical cell’s anion exchange membrane (AEM).

[0003] The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0004] To improve activation and / or operation of an electrolyzer equipped with an anion exchange membrane for carbon oxide reduction, conductivity of an anolyte solution may be assessed initially and / or on an ongoing basis, and then certain system modifications may be made when an elevated conductivity measurement above a desired setpoint conductivity or a reduced conductivity measurement below a desired setpoint conductivity is noted. The modifications in response to elevated conductivity include replacing the anolyte solution withwater; lowering the salt concentration of the anolyte solution; current modulation; or a combination thereof. Such measures may ensure adequate control of the residual salt exiting an anion exchange membrane during use; improving operation time as well as reliability while also decreasing the likelihood of electrolyzer failures. A method of preparing an electrochemical cell is provided which calibrates conductivity prior to start-up of an electrochemical cell to optimize working conditions of the cell; as well as a method for preparing an electrochemical cell for use.

[0005] Accordingly, in a first aspect, the present disclosure encompasses a method of operating an electrolyzer for carbon oxide reduction. In some embodiments, the method includes a) providing an electrochemical cell having a membrane electrode assembly, the membrane electrode assembly including: i) a cathode, ii) an anode, and iii) an anion exchange membrane disposed between the cathode and the anode; b) introducing an anolyte solution to the electrochemical cell such that the anolyte solution contacts the anion exchange membrane, the anolyte solution comprising a salt and being supplied from an anolyte reservoir; c) measuring conductivity of the anolyte solution; d) inletting a gas comprising a carbon oxide to the cathode of the membrane electrode assembly; and e) applying a current of a first current density to the membrane electrode assembly to thereby reduce the carbon oxide and produce a carbon- containing reduction product.

[0006] In some embodiments, the method also includes detecting that the conductivity of the anolyte solution is greater than a desired setpoint conductivity after initiating step e), where the conductivity of the anolyte solution is an elevated conductivity; and performing an anolyte restoration operation in response to the detection of the elevated conductivity, the anolyte restoration operation including one or more operations selected from (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt of the anolyte solution within the anolyte reservoir, and (iii) reducing the first current density to a second current density after step e).

[0007] In some embodiments, the method also includes detecting that the conductivity of the anolyte solution is greater than a desired setpoint conductivity after initiating step e), where the conductivity of the anolyte solution is an elevated conductivity; and performing an anolyte restoration operation in response to the detection of the elevated conductivity, the anolyte restoration operation including one or more operations selected from (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt of the anolyte solution within the anolyte reservoir, and (iii) reducing the first current density to a second current density after step e).

[0008] In some embodiments, the anolyte restoration operation is (i) replacing the anolyte solution with water within the anolyte reservoir.

[0009] In some embodiments, the method also includes circulating the water from the anolyte reservoir through the electrochemical cell; and delivering the anolyte solution from the electrochemical cell to the anolyte reservoir such that a concentration of the anolyte solution is diluted by the water provided to the anolyte reservoir.

[0010] In some embodiments, the anolyte restoration operation is (ii) lowering the concentration of the salt of the anolyte solution to a salt concentration that is greater than zero and less than 100 mM.

[0011] In some embodiments, the anolyte restoration operation is (iii) reducing the first current density to a second current density after step e).

[0012] In some embodiments, the first current density is greater than about 10 mA / cm2and wherein the second current density is about 5 mA / cm2or less.

[0013] In some embodiments, reducing the first current density to the second current density is accomplished all at once.

[0014] In some embodiments, reducing the first current density to the second current density is accomplished in multiple increments.

[0015] In some embodiments, reducing the first current density to the second current density is accomplished in a continuous ramp.

[0016] In some embodiments, the method also includes detecting that the conductivity of the anolyte solution is less than or equal to the desired setpoint conductivity after the anolyte restoration operation has been executed; and returning the current applied at step e) to the first current density in response to the detection of the conductivity of the anolyte solution being less than or equal to the desired setpoint conductivity after the anolyte restoration operation has been executed.

[0017] In some embodiments, returning the current applied at step e) to the first current density is accomplished all at once.

[0018] In some embodiments, returning the current applied at step e) to the first current density is accomplished in incremental current adjustments.

[0019] In some embodiments, returning the current applied at step e) to the first current density is accomplished by a continuous current ramp.

[0020] In some embodiments, step c) of measuring the conductivity of the anolyte solution is performed in the anolyte reservoir.

[0021] In some embodiments, the elevated conductivity is at least about 10% greater inmagnitude than the desired setpoint conductivity.

[0022] In some embodiments, the anolyte solution has about 100 mM or less of a salt.

[0023] In some embodiments, the salt includes alkali metal ions.

[0024] In some embodiments, the salt is an anion selected from the group consisting of phosphate, sulfate, carbonate, bicarbonate, and hydroxide.

[0025] In some embodiments, the salt includes ions of potassium, cesium, sodium, rubidium, or a combination thereof.

[0026] In some embodiments, the salt is magnesium carbonate, calcium carbonate, cesium carbonate, or potassium carbonate.

[0027] In some embodiments, the carbon oxide is carbon dioxide, carbon monoxide, or a combination thereof.

[0028] In some embodiments, the carbon-containing reduction product is carbon monoxide, a hydrocarbon, or an organic oxygen-containing compound.

[0029] In some embodiments, the gas supplied at step d) includes water vapor.

[0030] In some embodiments, the carbon oxide supplied at step d) is a humidified carbon oxide.

[0031] In a second aspect, the present disclosure encompasses a method of preparing an electrochemical cell. In some embodiments, the method includes a) activating an anion exchange membrane to form an activated anion exchange membrane; b) rinsing the activated anion exchange membrane with water for between about 1 hour and about 48 hours to form a rinsed activated anion exchange membrane; and c) assembling the electrochemical cell comprising a membrane electrode assembly, where the membrane electrode assembly includes: i) a cathode; ii) an anode; and iii) the rinsed activated anion exchange membrane disposed between the cathode and the anode.

[0032] In some embodiments, step a) includes soaking the anion exchange membrane in an 0.5 to 2 M solution of a first electrolyte for about 1 to 48 hours.

[0033] In some embodiments, the first electrolyte is potassium hydroxide, sodium hydroxide, or calcium hydroxide.

[0034] In some embodiments, the method also includes rinsing the anion exchange membrane with water and then soaking the anion exchange membrane for about 48 to 72 hours in an 0.5 to 2 M of a second electrolyte before step b).

[0035] In some embodiments, the second electrolyte is magnesium carbonate, calcium carbonate, or potassium carbonate.

[0036] In a third aspect, the present disclosure encompasses a method of activating anelectrochemical cell. In some embodiments, the method includes a) providing an electrochemical cell having a membrane electrode assembly, where the membrane electrode assembly includes i) a cathode, ii) an anode, and iii) an anion exchange membrane disposed between the cathode and the anode and in contact with an anolyte solution, wherein the anolyte solution has about 100 mM or less of a salt and wherein the anolyte solution is supplied from an anolyte reservoir; b) applying a first current density to the electrochemical cell; c) measuring conductivity of the anolyte solution in the electrochemical cell; d) detecting a conductivity of the anolyte solution greater than a desired setpoint conductivity, such conductivity representing an elevated conductivity; and e) performing an adjustment operation, the adjustment operation including one or more of: (i) replacing the anolyte solution with water,(ii) lowering a concentration of the salt in the anolyte solution within the anolyte reservoir, and(iii) reducing the first current density to a second current density, until the conductivity of the anolyte solution is reduced to less than or equal to the desired setpoint conductivity.

[0037] In some embodiments, step c) of measuring the conductivity of the anolyte solution is performed in the anolyte reservoir.

[0038] In some embodiments, the first current density is greater than about 10 mA / cm2and wherein the second current density is about 5 mA / cm2or less.

[0039] In some embodiments, reducing the first current density to the second current density is accomplished all at once.

[0040] In some embodiments, reducing the first current density to the second current density is accomplished in multiple increments.

[0041] In some embodiments, reducing the first current density to the second current density is accomplished in a continuous ramp.

[0042] In some embodiments, the adjustment operation is lowering a concentration of the salt in the anolyte solution within the anolyte reservoir to a salt concentration that is greater than zero and less than 100 mM.

[0043] In some embodiments, the elevated conductivity is at least about 10% greater in magnitude than the desired setpoint conductivity.

[0044] In some embodiments, the salt includes alkali metal ions.

[0045] In some embodiments, the salt includes an anion selected from the group consisting of phosphate, sulfate, carbonate, bicarbonate, and hydroxide.

[0046] In some embodiments, the salt includes ions of potassium, cesium, rubidium, or a combination thereof.

[0047] In some embodiments, the salt is magnesium carbonate, calcium carbonate, orpotassium carbonate.

[0048] In some embodiments, the desired setpoint conductivity is 400 pS / cm.

[0049] In some embodiments, the anion exchange membrane is an activated anion exchange membrane, and where the anion exchange membrane is activated by soaking the anion exchange membrane in an 0.5 to 2 M solution of a first electrolyte for about 1 to 48 hours; rinsing the anion exchange membrane with water; soaking the anion exchange membrane for about 1 to 72 hours in an 0.5 to 2 M of a second electrolyte; and then rinsing the anion exchange membrane with water for between about 1 hour and about 48 hours.

[0050] In a third aspect, the present disclosure encompasses a COXreduction reactor. In some embodiments, the COXreduction reactor includes an electrochemical cell, the electrochemical cell comprises a membrane electrode assembly including a) a cathode; b) an anode; and c) an anion exchange membrane disposed between the cathode and the anode; an anolyte reservoir for an anolyte salt solution; an anolyte salt solution recirculation loop; anolyte salt solution evacuation lines; a water reservoir; a water delivery line; a power supply for supplying a current density; a pump configured to circulate an anolyte salt solution; and an electrical conductivity measurement device configured to measure conductivity of the anolyte salt solution.

[0051] In some embodiments, the reactor is configured to perform an anolyte salt solution restoration operation.

[0052] In some embodiments, the anolyte salt solution restoration operation includes one or more operations selected from (i) replacing the anolyte salt solution with water, (ii) lowering a salt concentration of the anolyte salt solution within the anolyte reservoir, and (iii) reducing the current density.

[0053] These and other aspects are described further below with reference to the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 depicts a system for controlling the operation of a carbon oxide reduction reactor that may include a cell comprising a MEA in accordance with certain disclosed embodiments.

[0055] FIG. 2 illustrates an example MEA for use in COXreduction in accordance with certain disclosed embodiments.

[0056] FIG. 3 is a process flow diagram for a method of operating an electrolyzer for carbon oxide reduction in accordance with certain disclosed embodiments.

[0057] FIG. 4 is a process flow diagram for a method of preparing an electrochemical cell in accordance with certain disclosed embodiments.

[0058] FIG. 5 is a process flow diagram for a method of activating an electrochemical cell inaccordance with certain disclosed embodiments.

[0059] FIG. 6 depicts a system for measuring conductivity before or during the operation of a carbon oxide reduction reactor that may include a cell comprising a MEA and performing anolyte salt solution restoration or adjustment operations in accordance with certain disclosed embodiments.DETAILED DESCRIPTION

[0060] In the following description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments.Definitions

[0061] An “electrochemical cell” includes electrolyzers such as CO2 electrolyzers and water electrolyzers. It also includes some forms of CO2 purifiers, particularly those that employ faradaic reactions at an anode and / or a cathode.

[0062] A “carbon oxide” or “COx” includes carbon dioxide (CO2), carbon monoxide (CO), carbonate ions (COa2'), bicarbonate ions (HCOa'Xand any combinations thereof.

[0063] A “mixture” contains two or more components and unless otherwise stated may contain components other than the identified components.

[0064] It is understood that throughout this specification the identifiers such as “first”, “second” and “third” are used solely to aid in distinguishing the various components and / or steps of the disclosed subject matter. The identifiers “first”, “second” and “third” are not intended to imply any particular order, amount, preference or importance to the components and / or steps modified by these terms.Introduction & Overview

[0065] Electrolyzers containing polymer-based membrane electrode assemblies (MEAs) are designed to produce products through the electrochemical reduction of reactants at the cathode. For example, carbon oxide electrolyzers containing polymer-based MEAs are designed to produce oxygen at the anode from water and one or more carbon-based compounds through the electrochemical reduction of carbon dioxide or other carbon oxide at the cathode. As used herein, the term carbon oxide includes carbon dioxide (CO2), carbon monoxide (CO), carbonateions (CO32’), bicarbonate ions (HCOf), and any combinations thereof. Water electrolyzers containing polymer-based membrane electrode MEAs are designed to produce hydrogen at the cathode through the electrochemical reduction of water at the cathode. Many of the MEAs described below contain only an anion exchange polymer or multiple anion exchange polymers, optionally provided as a plurality of layers.

[0066] Various examples of MEAs and MEA-based carbon oxide electrolyzers are described in the following references: Published PCT Application No. 2017 / 192788, published November 9, 2017, and titled “REACTOR WITH ADVANCED ARCHITECTURE FOR THE ELECTROCHEMICAL REACTION OF CO2, CO, AND OTHER CHEMICAL COMPOUNDS,” Published PCT Application No. 2019 / 144135, published July 25, 2019, and titled “SYSTEM AND METHOD FOR CARBON DIOXIDE REACTOR CONTROL,” and US Patent No. 11,680,328, issued June 20, 2023, and titled “MEMBRANE ELECTRODE ASSEMBLY FOR COx REDUCTION,” each of which is incorporated herein by reference in its entirety.Carbon Oxide Electrolyzers

[0067] FIG. 1 depicts a system 100 for controlling the operation of a carbon oxide reduction reactor that may include a cell comprising a MEA. Carbon oxide reduction reactor 103 may include a cell comprising a MEA such as any one or more of those described herein. The reactor may contain multiple cells or MEAs arranged in a stack. System 100 includes an anode subsystem that interfaces with an anode of reduction reactor 103 and a cathode subsystem that interfaces with a cathode of reduction reactor 103. System 100 is an example of a system that may be used with or to implement any of the methods or operating conditions described above.

[0068] As depicted, the cathode subsystem includes a carbon oxide source 109 configured to provide a feed stream of carbon oxide to the cathode of reduction reactor 103, which, during operation, may generate an output stream that includes product(s) of a reduction reaction at the cathode. The product stream 108 may also include unreacted carbon oxide and / or hydrogen.

[0069] The carbon oxide source 109 is coupled to a carbon oxide flow controller 113 configured to control the volumetric or mass flow rate of carbon oxide to reduction reactor 103. One or more other components may be disposed on a flow path from flow carbon oxide source 109 to the cathode of reduction reactor 103. For example, an optional humidifier 104 may be provided on the path and configured to humidify the carbon oxide feed stream. Humidified carbon oxide may moisten one or more polymer layers of an MEA and thereby avoid drying such layers. Another component that may be disposed on the flow path is a purge gas inlet coupled to a purge gas source 117. In certain embodiments, purge gas source 117 is configuredto provide purge gas during periods when current is paused to the cell(s) of reduction reactor 103. In some implementations, flowing a purge gas over an MEA cathode facilitates recovery of catalyst activity and / or selectivity. This may be due, at least in part, to flushing certain reaction intermediates off catalyst active sites and / or remove water from the cathode. Examples of purge gases include carbon dioxide, carbon monoxide, hydrogen, nitrogen, argon, helium, oxygen, and mixtures of any two or more of these. MEAs are described in more detail with reference to FIG. 2 below.

[0070] Returning to FIG. 1, during operation, the output stream from the cathode flows via a conduit 107 that connects to a backpressure controller 115 configured to maintain pressure at the cathode side of the cell within a defined range (e.g., about 10 to 800 psig, depending on the system configuration). The output stream may provide the reaction products 108 to one or more components (not shown) for separation and / or concentration.

[0071] In certain embodiments, the cathode subsystem is configured to controllably recycle unreacted carbon oxide from the outlet stream back to the cathode of reduction reactor 103. In some implementations, the output stream is processed to remove reduction product(s) and / or hydrogen before recycling the carbon oxide. Depending upon the MEA configuration and operating parameters, the reduction product(s) may be carbon monoxide, hydrogen, hydrocarbons such as methane and / or ethylene, oxy gen-containing organic compounds such as formic acid, acetic acid, and any combinations thereof. In certain embodiments, one or more components, not shown, for removing water from the product stream are disposed downstream from the cathode outlet. Examples of such components include a phase separator configured to remove liquid water from the product gas stream and / or a condenser configured to cool the product stream gas and thereby provide a dry gas to, e.g., a downstream process when needed. In some implementations, recycled carbon oxide may mix with fresh carbon oxide from source 109 upstream of the cathode.

[0072] As depicted in FIG. 1, an anode subsystem is configured to provide an anode feed stream to an anode side of the carbon oxide reduction reactor 103. In certain embodiments, the anode subsystem includes an anode water source, not shown, configured to provide fresh anode water (also referred to as the anolyte solution herein) to a recirculation loop that includes an anode water reservoir 119 and an anode water flow controller 111. The anode water flow controller 111 is configured to control the flow rate of anode water to or from the anode of reduction reactor 103. In the depicted embodiment, the anode water recirculation loop is coupled to components for adjusting the composition of the anode water. These may include a water reservoir 121 and / or an anode water additives source 123. Water reservoir 121 isconfigured to supply water having a composition that is different from that in anode water reservoir 119 (and circulating in the anode water recirculation loop). In one example, the water in water reservoir 121 is pure water that can dilute solutes or other components in the circulating anode water. Pure water may be conventional deionized water even ultrapure water having a resistivity of, e.g., at least about 15 MOhm-cm or over 18.0 MOhm-cm. Anode water additives source 123 is configured to supply solutes such as salts and / or other components to the circulating anode water.

[0073] In various embodiments, an MEA contains an anode layer, a cathode layer, electrolyte, and optionally one or more other layers. The layers may be solids and / or gels. The layers may include polymers such as ion-conducting polymers.

[0074] When in use, the cathode of an MEA promotes electrochemical reduction of COXby combining three inputs: COX, ions (e.g., protons) that chemically react with COX, and electrons. The reduction reaction may produce CO, hydrocarbons, and / or oxygen and hydrogen containing organic compounds such as methanol, ethanol, and acetic acid. When in use, the anode of an MEA promotes an electrochemical oxidation reaction such as electrolysis of water to produce elemental oxygen and protons. The cathode and anode may each contain catalysts to facilitate their respective reactions.

[0075] The compositions and arrangements of layers in the MEA may promote high yield of COXreduction products. To this end, the MEA may facilitate any one or more of the following conditions: (a) minimal parasitic reduction reactions (non-COxreduction reactions) at the cathode; (b) low loss of COXreactants at anode or elsewhere in the MEA; (c) maintain physical integrity of the MEA during the reaction (e.g., prevent delamination of the MEA layers);(d) prevent COXreduction product cross-over; (e) prevent oxidation production (e.g., O2) crossover; (f) maintain a suitable environment at the cathode for oxidation; (g) provide pathway for desired ions to travel between cathode and anode while blocking undesired ions; and (h) minimize voltage losses. As explained herein, the presence of salts or salt ions in the MEA can facilitate some of all of these conditions.

[0076] An example MEA 200 for use in COXreduction is shown in FIG. 2. The MEA 200 has a cathode layer 220 and an anode layer 240 separated by an ion-conducting polymer layer 260 that provides a path for ions to travel between the cathode layer 220 and the anode layer 240. In certain embodiments, the cathode layer 220 includes an anion-conducting polymer and / or the anode layer 240 includes a cation-conducting polymer. In certain embodiments, the cathode layer and / or the anode layer of the MEA are porous. The pores may facilitate gas and / or fluid transport and may increase the amount of catalyst surface area that is available forreaction.

[0077] The ion-conducting layer 260 may include two or three sublayers: a polymer electrolyte membrane (PEM) 265, an optional cathode buffer layer 225, and / or an optional anode buffer layer 245. One or more layers in the ion-conducting layer may be porous. In certain embodiments, at least one layer is nonporous so that reactants and products of the cathode cannot pass via gas and / or liquid transport to the anode and vice versa. In certain embodiments, the PEM layer 265 is nonporous. Example characteristics of anode buffer layers and cathode buffer layers are provided elsewhere herein. In certain embodiments, the ion-conducting layer includes only a single layer or two sublayers.

[0078] In some embodiments, a carbon oxide electrolyzer anode contains a blend of oxidation catalyst and an anode ion-conducting polymer. There are a variety of oxidation reactions that can occur at the anode depending on the reactant that is fed to the anode and the anode catalyst(s). In one arrangement, the oxidation catalyst is selected from the group consisting of metals and oxides of Ti, Pt, Ir, Pt, Ni, Ru, Pd, Au, and alloys and combinations thereof, IrRu, Ptlr, Ni, NiFe, stainless steel, and combinations thereof. The oxidation catalyst can further contain conductive support particles selected from the group consisting of carbon, boron-doped diamond, and titanium.

[0079] The oxidation catalyst can be in the form of a structured mesh or can be in the form of particles. If the oxidation catalyst is in the form of particles, the particles can be supported by electronically conductive support particles. The conductive support particles can be nanoparticles. The conductive support particles may be compatible with the chemicals that are present in an electrolyzer anode when the CRR is operating and are oxidatively stable so that they do not participate in any electrochemical reactions. It is especially useful if the conductive support particles are chosen with the voltage and the reactants at the anode in mind. In some arrangements, the conductive support particles are titanium, which is well- suited for high voltages. In other arrangements, the conductive support particles are carbon, which can be most useful at low voltages. In general, such conductive support particles are larger than the oxidation catalyst particles, and each conductive support particle can support many oxidation catalyst particles. In one arrangement, the oxidation catalyst is iridium ruthenium oxide. Examples of other materials that can be used for the oxidation catalyst include, but are not limited to, those listed above. It should be understood that many of these metal catalysts can be in the form of oxides, especially under reaction conditions.

[0080] In some embodiments, the MEA has an anode layer comprising oxidation catalyst and a second ion-conducting polymer. The second ion-conducting polymer can comprise one ormore polymers that contain covalently bound, negatively charged functional groups configured to transport mobile positively charged ions. The second ion-conducting polymer can be selected from the group consisting of ethanesulfonyl fluoride, 2-[l-[difluoro- [(trifluoroethenyl)oxy] methyl] - 1 ,2,2,2-tetrafluoroethoxy]- 1 , 1 ,2,2,-tetrafluoro-, with tetrafluoroethylene, tetrafluoroethylene-perfluoro- 3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer, other perfluorosulfonic acid polymers and blends thereof. Examples of cationconducting polymers include e.g., Nafion 115, Nafion 117, and / or Nafion 211.

[0081] There may be tradeoffs in choosing the amount of ion-conducting polymer in the anode. It is important to include enough anode ion-conducting polymer to provide sufficient ionic conductivity. But it is also important for the anode to be porous so that reactants and products can move through it easily, and to maximize the amount of catalyst surface area that is available for reaction. In various arrangements, the ion-conducting polymer in the anode makes up approximately 50 wt % of the layer or between approximately 5 and 20 wt %, 10 and 90 wt %, between 20 and 80 wt %, between 25 and 70 wt %, or any suitable range. It is especially useful if the anode 240 can tolerate high voltages, such as voltages above about 1.2 V vs. a reversible hydrogen electrode. It is especially useful if the anode 240 is porous in order to maximize the amount of catalyst surface area available for reaction and to facilitate gas and liquid transport.

[0082] In one example of a metal catalyst, Ir or IrOx particles (100-200 nm) and Nafion ionomer form a porous layer approximately 10 pm thick. Metal catalyst loading is approximately 0.5-3 g / cm2.

[0083] In some embodiments, NiFeOx is used for basic reactions.COx Reduction Considerations

[0084] Polymer-based membrane assemblies such as MEAs have been used in various electrolytic systems such as water electrolyzers and in various galvanic systems such as fuel cells. However, COXreduction presents problems not encountered, or encountered to a lesser extent, in water electrolyzers and fuel cells.

[0085] For example, for many applications, an MEA for COXreduction requires a lifetime on the order of about 50,000 hours or longer (approximately five years of continuous operation), which is significantly longer than the expected lifespan of a fuel cell for automotive applications; e.g., on the order of 5,000 hours. And for various applications, an MEA for COXreduction employs electrodes having a relatively large surface area by comparison to MEAs used for fuel cells in automotive applications. For example, MEAs for COXreduction may employ electrodes having surface areas (without considering pores and other nonplanar features) of at least about 500 cm2.

[0086] COXreduction reactions may be implemented in operating environments that facilitate mass transport of particular reactant and product species, as well as to suppress parasitic reactions. Fuel cell and water electrolyzer MEAs often cannot produce such operating environments. For example, such MEAs may promote undesirable parasitic reactions such as gaseous hydrogen evolution at the cathode and / or gaseous CO2 production at the anode.

[0087] In some systems, the rate of a COXreduction reaction is limited by the availability of gaseous COXreactant at the cathode. By contrast, the rate of water electrolysis is not significantly limited by the availability of reactant: liquid water tends to be easily accessible to the cathode and anode, and electrolyzers can operate close to the highest current density possible.MEA Configurations

[0088] In certain embodiments, an MEA has a cathode layer, an anode layer, and a polymer electrolyte membrane (PEM) between the anode layer and the cathode layer. The polymer electrolyte membrane provides ionic communication between the anode layer and the cathode layer, while preventing electronic communication, which would produce a short circuit. The cathode layer includes a reduction catalyst and a first ion-conducting polymer. The cathode layer may also include an ion conductor and / or an electron conductor. The anode layer includes an oxidation catalyst and a second ion-conducting polymer. The anode layer may also include an ion conductor and / or an electron conductor. The PEM includes a third ion-conducting polymer.

[0089] In certain embodiments, the MEA has a cathode buffer layer between the cathode layer and the polymer electrolyte membrane. The cathode buffer includes a fourth ion-conducting polymer.

[0090] In certain embodiments, the MEA has an anode buffer layer between the anode layer and the polymer electrolyte membrane. The anode buffer includes a fifth ion-conducting polymer.

[0091] In connection with certain MEA designs, there are three available classes of ionconducting polymers: anion-conductors, cation-conductors, and mixed cation-and-anion- conductors. In certain embodiments, at least two of the first, second, third, fourth, and fifth ionconducting polymers are from different classes of ion-conducting polymers.Ion-conducting polymers for MEA layers

[0092] The term “ion-conducting polymer” is used herein to describe a polymer electrolyte having greater than about 1 mS / cm specific conductivity for anions and / or cations. The term “anion-conductor” describes an ion-conducting polymer that conducts anions primarily(although there will still be some small amount of cation conduction) and has a transference number for anions greater than about 0.85 at around 100 micron thickness. The terms “cationconductor” and / or “cation-conducting polymer” describe an ion-conducting polymer that conducts cations primarily (e.g., there can still be an incidental amount of anion conduction) and has a transference number for cations greater than approximately 0.85 at about 100 micron thickness. For an ion-conducting polymer that is described as conducting both anions and cations (a “cation-and-anion-conductor”), neither the anions nor the cations have a transference number greater than approximately 0.85 or less than approximately 0.15 at about 100 micron thickness. To say a material conducts ions (anions and / or cations) is to say that the material is an ion-conducting material or ionomer. Examples of ion-conducting polymers of each class are provided in the below Table 1.Table 1Polymeric structures

[0093] Examples of polymeric structures that can include an ionizable moiety or an ionic moiety and be used as ion-conducting polymers in the MEAs described here are provided below. The ion-conducting polymers may be used as appropriate in any of the MEA layers that include an ion-conducting polymer. Charge conduction through the material can be controlled by the type and amount of charge (e.g., anionic and / or cationic charge on the polymeric structure) provided by the ionizable / ionic moieties. In addition, the composition can include a polymer, a homopolymer, a copolymer, a block copolymer, a polymeric blend, other polymer- based forms, or other useful combinations of repeating monomeric units. As described below, an ion conducting polymer layer may include one or more of crosslinks, linking moieties, and arylene groups according to various embodiments. In some embodiments, two or more ion conducting polymers (e.g., in two or more ion conducting polymer layers of the MEA) may be crosslinked.

[0094] Non-limiting monomeric units can include one or more of the following:in which Ar is an optionally substituted arylene or aromatic; Ak is an optionally substituted alkylene, haloalkylene, aliphatic, heteroalkylene, or heteroaliphatic; and L is a linking moiety (e.g., any described herein) or can be -C(R7)(R8)-. Yet other non-limiting monomeric units can include optionally substituted arylene, aryleneoxy, alkylene, or combinations thereof, such as optionally substituted (aryl)(alkyl)ene (e.g., -Ak-Ar- or -Ak-Ar- Ak- or -Ar-Ak-, in which Ar is an optionally substituted arylene and Ak is an optionally substituted alkylene). One or more monomeric units can be optionally substituted with one or more ionizable or ionic moieties (e.g., as described herein).

[0095] One or more monomeric units can be combined to form a polymeric unit. Non-limiting polymeric units include any of the following:in which Ar, Ak, L, n, and m can be any described herein. In some embodiments, each m is independently 0 or an integer of 1 or more. In other embodiments, Ar can include two or more arylene or aromatic groups.

[0096] Other alternative configurations are also encompassed by the compositions herein, such as branched configurations, diblock copolymers, triblock copolymers, random or statistical copolymers, stereoblock copolymers, gradient copolymers, graft copolymers, and combinations of any blocks or regions described herein.

[0097] Examples of polymeric structures include those according to any one of formulas (I)- (V) and (X)-(XXXIV), or a salt thereof. In some embodiments, the polymeric structures are copolymers and include a first polymeric structure selected from any one of formulas (I)-(V) or a salt thereof; and a second polymeric structure including an optionally substituted aromatic, an optionally substituted arylene, a structure selected from any one of formulas (I)-(V) and (X)-(XXXIV), or a salt thereof.

[0098] In one embodiment, the MW of the ion-conducting polymer is a weight-average molecular weight (Mw) of at least 10,000 g / mol; or from about 5,000 to 2,500,000 g / mol. In another embodiment, the MW is a number average molecular weight (Mn) of at least 20,000 g / mol; or from about 2,000 to 2,500,000 g / mol.

[0099] In any embodiment herein, each of n, nl, n2, n3, n4, m, ml, m2, or m3 is, independently, 1 or more, 20 or more, 50 or more, 100 or more; as well as from 1 to 1,000,000, such as from 10 to 1,000,000, from 100 to 1,000,000, from 200 to 1,000,000, from 500 to 1,000,000, or from 1,000 to 1,000,000.

[0100] Non-limiting polymeric structures can include the following:or a salt thereof, wherein: each of R7, R8, R9, and R10is, independently, an electron- withdrawing moiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R7or R8can include the electron-withdrawingmoiety or wherein a combination of R7and R8or R9and R10can be taken together to form an optionally substituted cyclic group;Ar comprises or is an optionally substituted aromatic or arylene (e.g., any described herein); each of n is, independently, an integer of 1 or more; each of rings a-c can be optionally substituted; and rings a-c, R7, R8, R9, and R10can optionally comprise an ionizable or ionic moiety.

[0101] Further non-limiting polymeric structures can include one or more of the following:or a salt thereof, wherein:R7can be any described herein (e.g., for formulas (I)-(V)); n is from 1 or more; each L8A, LB, and LBis, independently, a linking moiety; and each X8A, X8A, X8A, XB, and XBis, independently, an ionizable or ionic moiety.

[0102] Yet other polymeric structures include the following:or a salt thereof, wherein: each of R1, R2, R3, R7, R8, R9, and R10is, independently, an electron- withdrawingmoiety, H, optionally substituted aliphatic, alkyl, heteroaliphatic, heteroalkylene, aromatic, aryl, or arylalkylene, wherein at least one of R7or R8can include the electron-withdrawing moiety or wherein a combination of R7and R8or R9and R10can be taken together to form an optionally substituted cyclic group; each Ak is or comprises an optionally substituted aliphatic, alkylene, haloalkylene, heteroaliphatic, or hetero alkylene; each Ar is or comprises an optionally substituted arylene or aromatic; each of L, L1, L2, L3, and L4is, independently, a linking moiety; each of n, nl, n2, n3, n4, m, ml, m2, and m3 is, independently, an integer of 1 or more; q is 0, 1, 2, or more; each of rings a-i can be optionally substituted; and rings a-i, R7, R8, R9, and R10can optionally include an ionizable or ionic moiety.

[0103] In particular embodiments (e.g., of formula (XIV) or (XV)), each of the nitrogen atoms on rings a and / or b are substituted with optionally substituted aliphatic, alkyl, aromatic, aryl, an ionizable moiety, or an ionic moiety. In some embodiments, one or more hydrogen or fluorine atoms (e.g., in formula (XIX) or (XX)) can be substituted to include an ionizable moiety or an ionic moiety (e.g., any described herein). In other embodiments, the oxygen atoms present in the polymeric structure (e.g., in formula XXVIII) can be associated with an alkali dopant (e.g., K+).

[0104] In particular examples, Ar, one or more of rings a-i (e.g., rings a, b,f, g, h, or z), L, L1, L2, L3, L4, Ak, R7, R8, R9, and / or R10can be optionally substituted with one or more ionizable or ionic moieties and / or one or more electron-withdrawing groups. Yet other non-limiting substituents for Ar, rings (e.g., rings a-i), L, Ak, R7, R8, R9, and R10include one or more described herein, such as cyano, hydroxy, nitro, and halo, as well as optionally substituted aliphatic, alkyl, alkoxy, alkoxyalkyl, amino, aminoalkyl, aryl, arylalkylene, aryloyl, aryloxy, arylalkoxy, hydroxyalkyl, and haloalkyl.

[0105] In some embodiments, each of R1, R2, and R3is, independently, H, optionally substituted aromatic, aryl, aryloxy, or arylalkylene. In other embodiments (e.g., of formulas (I)-(V) or (XII)), R7includes the electron-withdrawing moiety. In yet other embodiments, R8, R9, and / or R10includes an ionizable or ionic moiety.

[0106] In one instance, a polymeric subunit can lack ionic moieties. Alternatively, the polymeric subunit can include an ionic moiety on the Ar group, the L group, both the Ar and L groups, or be integrated as part of the L group. Non-limiting examples of ionizable and ionic moieties include cationic, anionic, and multi-ionic group, as described herein.

[0107] In any embodiment herein, the electron- withdrawing moiety can include or be an optionally substituted haloalkyl, cyano (CN), phosphate (e.g., -O(P=O)(ORpl)(ORp2) or -O- [P(=O)(ORP1)-O]P3-RP2), sulfate (e.g., -O-S(=O)2(ORS1)), sulfonic acid (-SO3H), sulfonyl (e.g., -SO2-CF3), difluoroboranyl (-BF2), borono (B(OH)2), thiocyanato (-SCN), or piperidinium. Yet other non-limiting phosphate groups can include derivatives of phosphoric acid, such as orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, and / or phosphoric anhydride, or combinations thereof.

[0108] Yet other polymeric units can include poly(benzimidazole) (PBI), polyphenylene (PP), polyimide (PI), poly(ethyleneimine) (PEI), sulfonated polyimide (SPI), polysulfone (PSF), sulfonated polysulfone (SPSF), poly(ether ether ketone) (PEEK), PEEK with cardo groups (PEEK-WC), polyethersulfone (PES), sulfonated polyethersulfone (SPES), sulfonated poly(ether ether ketone) (SPEEK), SPEEK with cardo groups (SPEEK-WC), poly(p-phenylene oxide) (PPO), sulfonated polyphenylene oxide (SPPO), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), poly(epichlorohydrin) (PECH), poly(styrene) (PS), sulfonated poly(styrene) (SPS), hydrogenated poly (butadiene- styrene) (HPBS), styrene divinyl benzene copolymer (SDVB), styrene-ethylene-butylene-styrene (SEBS), sulfonated bisphenol-A- poly sulfone (SPSU), poly(4-phenoxy benzoyl- 1,4-phenylene) (PPBP), sulfonated poly(4- phenoxy benzoyl- 1,4-phenylene) (SPPBP), poly(vinyl alcohol) (PVA), poly(phosphazene), poly(aryloxyphosphazene), polyetherimide, as well as combinations thereof.

[0109] MEAs may include a polymer electrolyte membrane (PEM) disposed between and conductively coupled to the anode catalyst layer and the cathode catalyst layer. In certain embodiments, a polymer electrolyte membrane has high ionic conductivity (e.g., greater than about 1 mS / cm) and is mechanically stable. Mechanical stability can be evidenced in a variety of ways such as through high tensile strength, modulus of elasticity, elongation to break, and tear resistance. Many commercially available membranes can be used for the polymer electrolyte membrane. Examples include, but are not limited to, various Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion ® (PFSA) (Solvay).

[0110] In one arrangement, the PEM comprises at least one ion-conducting polymer that is a cation-conductor. The third ion-conducting polymer can comprise one or more covalently- bound, negatively-charged functional groups configured to transport mobile positively-charged ions. The third ion-conducting polymer can be selected from the group consisting of ethanesulfonyl fluoride, 2-[l-[difluoro-[(trifluoroethenyl)oxy]methyl]- 1 ,2,2,2- tetrafluoroethoxy]-l,l,2,2,-tetrafluoro-, with tetrafluoroethylene, tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer, other perfluoro sulfonic acid polymers and blends thereof.

[0111] When the polymer electrolyte membrane is a cation conductor (e.g., it conducts protons), it may contain a high concentration of protons during operation of the CRR, while a cathode may operate better when a low concentration of protons is present. A cathode buffer layer may be provided between the polymer electrolyte membrane and the cathode to provide a region of transition from a high concentration of protons to a low concentration of protons. In one arrangement, a cathode buffer layer is an ion-conducting polymer with many of the same properties as the ion-conducting polymer in the cathode. A cathode buffer layer may provide a region for the proton concentration to transition from a polymer electrolyte membrane, which has a high concentration of protons, to the cathode, which has a low proton concentration. Within the cathode buffer layer, protons from the polymer electrolyte membrane may encounter anions from the cathode, and they may neutralize one another. The cathode buffer layer may help ensure that a deleterious number of protons from the polymer electrolyte membrane does not reach the cathode and raise the proton concentration. If the proton concentration of the cathode is too high, COXreduction does not occur. A high proton concentration may be a concentration in the range of about 10 to 0.1 molar and low proton concentration may be a concentration of less than about 0.01 molar.

[0112] A cathode buffer layer can include a single polymer or multiple polymers. If the cathode buffer layer includes multiple polymers, the multiple polymers can be mixed together or can be arranged in separate, adjacent layers. Examples of materials that can be used for the cathode buffer layer include, but are not limited to, FumaSep FAA-3, Tokuyama anion exchange membrane material, and poly ether-based polymers, such as polyethylene oxide (PEO), and blends thereof. Further examples are given above in the discussion of the cathode catalyst layer.

[0113] The thickness of the cathode buffer layer is chosen to be sufficient that COXreduction activity is high due to the proton concentration being low. This sufficiency can be different for different cathode buffer layer materials. In general, the thickness of the cathode buffer layer is between approximately 200 nm and 100 pm, between 300 nm and 75 pm, between 500 nm and 50 pm, or any suitable range.

[0114] In some embodiments, the cathode buffer layer is less than 50 pm, for example between 1-25 pm such between 1-5 pm, 5-15 pm, or 10-25 pm. By using a cathode buffer layer in this range of thicknesses, the proton concentration in the cathode can be reduced while maintaining the overall conductivity of the cell. In some embodiments, an ultra-thin layer (100nm-1 pm and in some embodiments, sub-micron) may be used. And as discussed above, in some embodiments, the MEA does not have a cathode buffer layer. In some such embodiments, anion-conducting polymer in the cathode catalyst layer is sufficient. The thickness of the cathode buffer layer may be characterized relative to that of the PEM.

[0115] Water and CO2 formed at the interface of a cathode buffer layer and a PEM can delaminate the MEA where the polymer layers connect. The delamination problem can be addressed by employing a cathode buffer layer having inert filler particles and associated pores. One possible explanation of its effectiveness is that the pores create paths for the gaseous carbon dioxide to escape back to the cathode where it can be reduced.

[0116] Materials that are suitable as inert filler particles include, but are not limited to, TiO2, silica, PTFE, zirconia, and alumina. In various arrangements, the size of the inert filler particles is between 5 nm and 500 pm, between 10 nm and 100 pm, or any suitable size range. The particles may be generally spherical.

[0117] If PTFE (or other filler) volume is too high, it will dilute the polymer electrolyte to the point where ionic conductivity is low. Too much polymer electrolyte volume will dilute the PTFE to the point where it does not help with porosity. In many embodiments a mass ratio of polymer electrolyte / PTFE is 0.25 to 2, and more particularly, 0.5 to 1. A volume ratio polymer electrolyte / PTFE (or, more generally, polymer electrolyte / inert filler) may be 0.25 to 3, 0.5 to 2, 0.75 to 1.5, or 1.0 to 1.5.

[0118] In other arrangements, porosity is achieved by using particular processing methods when the layers are formed. One example of such a processing method is laser ablation, where nano to micro- sized channels are formed in the layers. Another example is mechanically puncturing a layer to form channels through it.

[0119] In one arrangement, the cathode buffer layer has a porosity between 0.01% and 95% (e.g., approximately between, by weight, by volume, by mass, etc.). However, in other arrangements, the cathode buffer layer can have any suitable porosity (e.g., between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%). In some embodiments, the porosity is 50% or less, e.g., 0.1-50%, 5-50%, 20-50%, 5-40%, 10-40%, 20-40%, or 25%-40%. In some embodiments, the porosity is 20% or below, e.g. 0.1-20%, 1-10%, or 5-10%.

[0120] Porosity may be measured as described above with respect to the catalyst layer, including using mass loadings and thicknesses of the components, by methods such as mercury porosimetry, x-ray diffraction (SAXS or WAXS), and image processing on TEM images to calculate filled space vs. empty space. Porosity is measured when the MEA is completely dry as the materials swell to varying degrees when exposed to water during operation.

[0121] Porosity in layers of the MEA, including the cathode buffer layer, is described further below.Anode buffer layer

[0122] In some CRR reactions, bicarbonate is produced at the cathode. It can be useful if there is a polymer that blocks bicarbonate transport somewhere between the cathode and the anode, to prevent migration of bicarbonate away from the cathode. It can be that bicarbonate takes some CO2 with it as it migrates, which decreases the amount of CO2 available for reaction at the cathode. In some MEAs, the polymer electrolyte membrane includes a polymer that blocks bicarbonate transport. Examples of such polymers include, but are not limited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion ® (PFSA) (Solvay). In some MEAs, there is an anode buffer layer between the polymer electrolyte membrane and the anode, which blocks transport of bicarbonate. If the polymer electrolyte membrane is an anion-conductor, or does not block bicarbonate transport, then an additional anode buffer layer to prevent bicarbonate transport can be useful. Materials that can be used to block bicarbonate transport include, but are not limited to Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), and Aquivion ® (PFSA) (Solvay). Of course, including a bicarbonate blocking feature in the ion-exchange layer is not particularly desirable if there is no bicarbonate in the CRR.

[0123] In certain embodiments, an anode buffer layer provides a region for proton concentration to transition between the polymer electrolyte membrane to the anode. The concentration of protons in the polymer electrolyte membrane depends both on its composition and the ion it is conducting. For example, a Nafion polymer electrolyte membrane conducting protons has a high proton concentration. A FumaSep FAA-3 polymer electrolyte membrane conducting hydroxide has a low proton concentration. For example, if the desired proton concentration at the anode is more than 3 orders of magnitude different from the polymer electrolyte membrane, then an anode buffer layer can be useful to affect the transition from the proton concentration of the polymer electrolyte membrane to the desired proton concentration of the anode. The anode buffer layer can include a single polymer or multiple polymers. If the anode buffer layer includes multiple polymers, the multiple polymers can be mixed together or can be arranged in separate, adjacent layers. Materials that can be useful in providing a region for the pH transition include, but are not limited to, Nafion, FumaSep FAA-3, Sustainion®, Tokuyama anion exchange polymer, and polyether-based polymers, such as polyethylene oxide (PEG), blends thereof, and / or any other suitable materials. High proton concentration is considered to be in the range of approximately 10 to 0.1 molar and low concentration isconsidered to be less than approximately 0.01 molar. Ion-conducting polymers can be placed in different classes based on the type(s) of ions they conduct. This has been discussed in more detail above. There are three classes of ion-conducting polymers described in Table 1 above. In one embodiment of the invention, at least one of the ion-conducting polymers in the cathode, anode, polymer electrolyte membrane, cathode buffer layer, and anode buffer layer is from a class that is different from at least one of the others.

[0124] It can be useful if some or all of the following layers are porous: the cathode, the cathode buffer layer, the anode and the anode buffer layer. In some arrangements, porosity is achieved by combining inert filler particles with the polymers in these layers. Materials that are suitable as inert filler particles include, but are not limited to, TiCh, silica, PTFE, zirconia, and alumina. In various arrangements, the size of the inert filler particles is between 5 nm and 500 pm, between 10 nm and 100 pm, or any suitable size range. In other arrangements, porosity is achieved by using particular processing methods when the layers are formed. One example of such a processing method is laser ablation, where nano to micro-sized channels are formed in the layers. Laser ablation can additionally or alternatively achieve porosity in a layer by subsurface ablation. Subsurface ablation can form voids within a layer, upon focusing the beam at a point within the layer, and thereby vaporizing the layer material in the vicinity of the point. This process can be repeated to form voids throughout the layer, and thereby achieving porosity in the layer. The volume of a void is preferably determined by the laser power (e.g., higher laser power corresponds to a greater void volume) but can additionally or alternatively be determined by the focal size of the beam, or any other suitable laser parameter. Another example is mechanically puncturing a layer to form channels through the layer. The porosity can have any suitable distribution in the layer (e.g., uniform, an increasing porosity gradient through the layer, a random porosity gradient, a decreasing porosity gradient through the layer, a periodic porosity, etc.).

[0125] The porosities (e.g., of the cathode buffer layer, of the anode buffer layer, of the membrane layer, of the cathode layer, of the anode layer, of other suitable layers, etc.) of the examples described above and other examples and variations preferably have a uniform distribution, but can additionally or alternatively have any suitable distribution (e.g., a randomized distribution, an increasing gradient of pore size through or across the layer, a decreasing gradient of pore size through or across the layer, etc.). The porosity can be formed by any suitable mechanism, such as inert filler particles (e.g., diamond particles, boron-doped diamond particles, polyvinylidene difluoride / PVDF particles, polytetrafluoroethylene / PTFE particles, etc.) and any other suitable mechanism for forming substantially non-reactive regionswithin a polymer layer. The inert filler particles can have any suitable size, such as a minimum of about 10 nanometers and a maximum of about 200 nanometers, and / or any other suitable dimension or distribution of dimensions.

[0126] As discussed above, the cathode buffer layer preferably has a porosity between about 1 and 90 percent by volume but can additionally or alternatively have any suitable porosity (including, e.g., no porosity). However, in other arrangements and examples, the cathode buffer layer can have any suitable porosity (e.g., between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1- 90%, etc.), in some embodiments, the porosity is 20% or below, e.g. 0.1-20%, 1-10%, or 5- 10%.

[0127] In some embodiments, the cathode buffer layer is porous but at least one layer between the cathode layer and the anode layer is nonporous. This can prevent the passage of gases and / or bulk liquid between the cathode and anode layers while still preventing delamination. For example, the nonporous layer can prevent the direct passage of water from the anode to the cathode.

[0128] In some implementations, an MEA cell configured to produce methane from carbon dioxide employs a sodium containing salt and is operated in a manner that produces products at the cathode having at least about 50 mole% methane or at least about 70 mole% methane. Other products that may be produced at the cathode include hydrogen, carbon monoxide, one or more two or more carbon organic molecules, and the like. An MEA cell configured to produce methane may comprise copper or other transition metal at the cathode. An MEA cell configured to produce methane may comprise a bipolar membrane assembly.

[0129] In some implementations, an MEA cell configured to produce ethylene and / or other organic compounds having two or more carbon atoms from carbon dioxide employs a potassium, cesium, or rubidium-containing salt and is operated in a manner that produces products at the cathode having at least about 60 mole % ethylene and / or other organic compounds having two or more carbon atoms or at least about 80 mole % ethylene and / or other organic compounds having two or more carbon atoms. Other products that may be produced at the cathode include hydrogen, methane, and carbon monoxide. An MEA cell configured to produce ethylene and / or other organic compounds having two or more carbon atoms may comprise copper or other transition metal at the cathode. An MEA cell configured to produce ethylene and / or other organic compounds having two or more carbon atoms may comprise a bipolar membrane assembly.

[0130] In certain embodiments, the voltage efficiency and / or the product selectivity for methane or organic compound production in an MEA cell employing a sodium, potassium,cesium, or rubidium containing salt in water does not decrease by more than about 1%, or by more than about 0.3%, or by more than about 0.01%, over 90 A-hr.

[0131] The cathode catalysts described herein include alloys, doped materials, and other variants of the listed material. For example, an MEA cathode catalyst described as containing gold or other noble metal is understood to include alloys, doped metals, and other variants of gold or other noble metals. Similarly, an MEA cathode catalyst described as containing copper or other transition metal is understood to include alloys, doped metals, and other variants of copper or other transition metals.Salts

[0132] The introduction of salt ions may affect the carbon oxide electrolysis performance through any of several possible mechanisms. While not wishing to be bound by theory, the following is a list of example mechanisms by which salts may influence operation of an MEA cell during electrolytic carbon oxide reduction.

[0133] The presence of cations and / or anions from a salt reduces the activation energy of one or more catalytic pathways. This may be due to any of many possible mechanisms. For example, a salt may change the local electrolyte structure and / or electron density on the catalyst surface. It has been observed that salt ions increase in Faradaic yield in some carbon oxide reduction systems. It has also been observed that the presence of particular ions changes the selectivity of a catalyst for one reaction over another.

[0134] Cations and / or anions from a salt may help hydrate polymer-electrolyte, particularly anion exchange polymers. Ions travel as hydrates; i.e., they carry water molecules with them as they move across polymer layers. Hydration of the MEA, and particularly portions of the MEA close to the cathode catalyst, may facilitate the reduction reaction by preventing the flowing carbon oxide from evaporating water in the MEA. In general, salt ions may promote hydration of the MEA, particularly at regions of the MEA susceptible to drying. In various embodiments, the presence of salt in the polymer renders the polymer more hygroscopic.

[0135] The presence of salts and the ions from a salt may increase the conductivity of one or more MEA layers. In particular, the ions may increase the conductivity of anion exchange polymers, which tend to have relatively low conductivity compared to cation exchange polymers. Increasing conductivity of the polymers may reduce the overall resistance of the MEA cell.

[0136] The presence of a salt may raise the pH of one or more polymer-electrolyte layers. This should be compared with proton donating additives, which lower the polymers’ pH.

[0137] The presence of cations and / or anions from a salt changes water uptake and swelling of 1polymer electrolyte layers. If volumetric changes due to swelling are mismatched between the anode side and the cathode side of an MEA, mechanical stress on the MEA can degrade cell performance. In certain embodiments, the presence of a salt at a defined concentration tunes the relative amounts of swelling in two or more different layers of an MEA to equalize the swelling exhibited by these layers.

[0138] The presence of cations and / or anions provided by salts may change the conductivity at the interface between two layers of the MEA. In a bipolar interface, for example, protons may have to jump across an interfacial gap to meet anions. This jump has an associated resistance. The presence of a salt may decrease the barrier to protons and anions coming together across the interface. Note that pores in Nafion and similar polymers have sulfonic acid groups to allow protons to move with low resistance. At a bipolar interface, these groups are not present to facilitate continued movement. A salt can provide a non-charge depleted region at the interface to facilitate protons and anions coming together (e.g., protons come from the anode side and react with bicarbonate ions from the cathode side). Stated another way, a salt solution present at the interface may provide a conductive bridge or and ionically conductive bridge between the anion conducting polymer and the cation conducting polymer.

[0139] Cations and / or anions provided by a salt may provide a counter ion for charged carbonbased species formed by the cathode reduction reaction. Such charged species require an available counter ion to maintain charge neutrality. In some implementations, the reduction reaction at the cathode produces a carboxylate product (e.g., formate, oxalate, or acetate). However, if there are relatively few available cations, the reaction may be disfavored. This may be the case where the cathode layer comprises an anion exchange polymer, such as an anion exchange membrane (AEM), which blocks the flux of protons (potential counterions). Cations donated by a salt may provide the needed species to facilitate carboxylate-producing reactions.

[0140] A salt concentration gradient may induce osmotic pressure. For example, the salt concentration may be greater on the anode side, which draws water away from the cathode and thereby reduces the occurrence of cathode flooding. Note that water present on the cathode side may be provided, at least in part, by reaction of hydrogen ions and bicarbonate ions in the MEA interior. This water does not initially have salt ions, which contributes to the concentration gradient.

[0141] Various types of salt may be used in an MEA cell. Such salts may have inorganic or organic cations and anions. The salt composition may affect cell operating conditions such as overpotential, Faradaic efficiency, and / or selectivity among multiple carbon oxide reductionreactions. Various factors influencing the choice of salt composition are described herein.

[0142] The salt composition may depend on the catalyst used at the cathode. In certain embodiments, the salt does not contain a cation that could poison the cathode catalyst. For example, the salt may not contain a cation that could be reduced at a cathode catalyst such as a catalyst comprising gold or another noble metal. Such catalysts are sometimes used in MEA cells configured to reduce carbon dioxide to carbon monoxide or other reduction product. It has been found that reduction of metal ions such as iron or other transition metal ions on catalyst particles can poison the catalyst or otherwise decrease the catalytic conversion of carbon dioxide to a reduction product such as carbon monoxide.

[0143] In certain embodiments, a salt employed in a carbon oxide reduction reactor contains only cations that are not reducible in an aqueous medium to elemental metal under operating conditions for carbon dioxide reduction at a cathode. In certain embodiments, a salt employed in the reactor does not have transition metal ions. In certain embodiments, a salt employed in the reactor has only alkali metal cations and / or alkaline earth element cations.

[0144] While generation of carbon monoxide from carbon dioxide may be performed with a gold or silver catalyst, generation of hydrocarbons and / or organic oxygen-containing compounds from a carbon oxide may be performed with a copper or other transition metal catalyst at the cathode. In some cases, a salt employed in a cell configured to produce hydrocarbons and / or organic oxygen-containing compounds has one or more cations that are not alkali metal ions or alkaline earth element ions. For example, an MEA with a transition metal catalyst may be configured with a salt comprising one or more transition metals.

[0145] The types of salts used as well as their concentration may vary depending upon whether the carbon oxide reduction reactor is one that uses a bipolar MEA, one that uses an anion exchange polymer only MEA, or one that uses some other MEA configuration. A cell configured to reduce carbon monoxide may employ an anion exchange polymer only MEA because little or no bicarbonate is formed at the cathode and so the MEA need not include a cation-conducting polymer to block bicarbonate transport to the anode where it could liberate carbon dioxide that would otherwise be used in a reduction reaction at the cathode. Such cells may employ salts that contain cations of transition metals or other metals that might poison a noble metal catalyst. In certain embodiments, a carbon dioxide reduction cell having a bipolar MEA employs a salt that does not have transition metal ions.

[0146] In certain embodiments, the salt contains a cation that adjusts the pH at one or more locations in a carbon oxide reducing cell (e.g., at the anode, the cathode, or an intermediate ionically conductive polymer layer). In some cases, during operation, the salt adjusts the pH tobe more acidic or more basic at one or more such locations. In certain embodiments, the anion is ammonium, a derivatized ammonium cation such as a quaternary ammonium ion, an alkali metal ion, or an alkaline earth metal ion.

[0147] The salt composition may be influenced by the reaction at the anode of a carbon dioxide reduction cell. In certain embodiments, a salt contains an anion that does not readily oxidize at the anode and / or does not readily reduce at the cathode under operating conditions of the cell. In certain embodiments, the anion is not a halide. In some cases, the anion is not chloride, bromide, or iodide. Halides potentially oxidize at the anode where they could form elemental halogen. Note that in certain embodiments, however, a halide is used in a carbon dioxide reduction cell where the reduction product is a halogenated compound. In certain embodiments, a salt has an anion that is not an oxidizable nitrogen-containing anion such as a nitrite or an amine. In certain embodiments, a salt has an anion that is not an organic anion; for example, the salt does not contain a carboxylate ion.

[0148] In certain embodiments, the salt contains an anion that adjusts the pH at one or more locations in a carbon oxide reducing cell (e.g., at the anode, the cathode, or an intermediate ionically conductive polymer layer). In some cases, during operation, the salt adjusts the pH to be more acidic or more basic at one or more such locations. In certain embodiments, the anion is hydroxide, bicarbonate, sulfite, or sulfate.

[0149] One consideration in choosing the cation and / or an anion of a salt is the ion’s mobility. In certain embodiments, the ion has a relatively high mobility in the polymers of an ME A. In some cases, one or more layers of an MEA with the salt present each have an ionic conductivity of at least about 4 mS / cm. In some implementations, ions that are relatively small in atomic weight are used. In some cases, the cation of the salt has an atomic or molecular weight of about 140 or lower, or about 90 or lower, or about 40 or lower. In some cases, the anion of the salt has an atomic or molecular weight of about 100 or lower.

[0150] In certain embodiments, the salt is relatively soluble in aqueous media. For example, the salt may have a solubility of at least about 1 mol / L, or least about 2 mol / L, or at least about 10 mol / L in otherwise deionized water at 25°C.

[0151] The type of the salt can impact product selectivity in an MEA cell. The choice of one cation over another may change the ratio of one product over another by, e.g., at least about 10%.

[0152] In certain embodiments, a sodium-containing salt such as sodium bicarbonate when used in an MEA cell with a gold catalyst on the cathode selectively increases production of carbon monoxide over the byproduct hydrogen during carbon dioxide reduction. This increasein carbon monoxide production is observed in comparison to similar gold catalyst-containing MEA cells containing no salt. For example, an MEA cell having a gold catalyst and employing sodium bicarbonate may increase the carbon monoxide production by at least about 100% when compared to a similar MEA cell that uses no salt. In other words, an MEA cell employing a sodium-containing salt such as sodium bicarbonate generates carbon monoxide in a molar quantity that is at least about two-fold higher than that produced by the same MEA cell operated in the same way but with substantially no salt. In some embodiments, the MEA cell employing a sodium containing salt generates carbon monoxide in a molar quantity that is at least about three-fold higher. In some cases, an MEA cell employing a potassium containing salt such as potassium bicarbonate generates carbon monoxide in a molar quantity that is at least about twofold higher than that produced by the same MEA cell operated in the same way but with substantially no salt. In some cases, an MEA cell employing a salt with higher atomic weight alkali metal such as cesium or rubidium generates carbon monoxide in a molar quantity that is at least about two-fold higher than that produced by the same MEA cell operated in the same way but with substantially no salt.

[0153] In some implementations, an MEA cell configured to produce carbon monoxide from carbon dioxide employs an alkali metal containing salt and is operated in a manner that produces products at the cathode having at least about 70 mole % carbon monoxide or at least about 80 mole % carbon monoxide among various products, but not including unreacted carbon dioxide. Other products that may be produced at the cathode include hydrogen, one or more hydrocarbons, one or more carbonyl-containing products, and the like. An MEA cell configured to produce carbon monoxide may comprise gold, silver, or other noble metal at the cathode. An MEA cell configured to produce carbon monoxide may comprise a bipolar membrane assembly.

[0154] In certain embodiments, the concentration of a sodium, potassium, cesium, or rubidium containing salt in water delivered to an MEA cell is about 1 mM to 20 mM. This concentration range may apply to MEA cells configured to produce carbon monoxide from carbon dioxide. In certain embodiments, such cells comprise a gold or other noble metal as a cathode catalyst. As used herein, a noble metal is a metal that strongly resists chemical action. Examples include platinum and silver, in addition to gold.

[0155] In some cases, MEA cells with relatively smaller surface areas (e.g., about 10 cm2to about 50 cm2assuming a planar face) skew to a relatively lower concentration range, such as from about 1 mM to 5 mM, while MEA cells with relatively larger surface areas (e.g., about 50 cm2to about 1000 cm2) skew to a relatively higher concentration range, such as from about5 inM to 20 mM.

[0156] In certain embodiments, a salt such as sodium bicarbonate when supplied via anode water to an MEA cell with a gold catalyst on the cathode improves energy efficiency by about 9%-25%. Further, in certain embodiments, desirable levels of selectivity for CO and cell voltage, observed during initial operation of a cell, are more than an order of magnitude more stable when the salt solution is used.

[0157] In some cases, an MEA cell employing a sodium containing salt such as sodium bicarbonate has a voltage efficiency for producing carbon monoxide that is at least about 5% higher than the voltage efficiency of the same MEA cell operated in the same way but with substantially no salt. In some cases, the MEA cell employing a sodium containing salt such as sodium bicarbonate has a voltage efficiency for producing carbon monoxide that is at least about 10% higher, or at least about 20% higher, than the voltage efficiency of the same MEA cell operated in the same way but with no substantially salt. In some cases, an MEA cell employing a potassium containing salt such as potassium bicarbonate has a voltage efficiency for producing carbon monoxide that is at least about 5% higher than the voltage efficiency of the same MEA cell operated in the same way but with substantially no salt. In some cases, an MEA cell employing a salt with a higher atomic weight alkali metal such as cesium or rubidium has a voltage efficiency for producing carbon monoxide that is at least about 5% higher than the voltage efficiency of the same MEA cell operated in the same way but with substantially no salt. In certain embodiments, the voltage efficiency for producing carbon monoxide in a bipolar MEA having gold or other noble metal cathode catalyst is at least about 25%.

[0158] As an example, a tested cell with no salt in the anode water has an average voltage of 3.86V and an average CO Faradaic yield of 0.53 for the first hour at 0.5A / cm2and decay rate of 144 mV / hour and 0.018 CO Faradaic yield / hour for hours 2-5 at 500mA / cm2. In comparison, the same cell operated with 2mM NaHCOa has an average voltage of 3.52 V and an average CO Faradaic yield of 0.936 for the first hour at 0.5A / cm2and decay rate of 15.5 mV / hour and 0.001 CO Faradaic yield / hour for hours 2-5 at 500mA / cm2. In certain embodiments, an MEA cell configured to produce carbon monoxide from carbon dioxide has an average voltage of at most about 3.6 V for the first hour of operation and a decay rate of no more than about 16 mV / hour for hours 2-5.

[0159] In certain embodiments, the voltage efficiency and / or the product selectivity for carbon monoxide production in an MEA cell employing a sodium, potassium, cesium, or rubidium containing salt in water is stable over a period of operation that is at least 10 times longer than that of a corresponding MEA cell operated in the same way, over the same period, but withsubstantially no salt. In certain embodiments, the voltage for carbon monoxide production in an MEA cell employing an aqueous sodium, potassium, cesium, or rubidium containing salt does not increase by more than about 0.5%, or by more than aboutl6 mV per hour, at an applied current density of 600 mA / cm2or lower for more than 8 hours of operation. In certain embodiments, the mole fraction of carbon monoxide among all other products (excluding carbon dioxide) produced at the cathode of an MEA cell employing an aqueous sodium, potassium, cesium, or rubidium containing salt does not decrease by more than about 1 % per hour, at an applied current density of 600 mA / cm2or lower for more than 8 hours of operation. In certain embodiments, the voltage for carbon monoxide production in an MEA cell employing an aqueous sodium, potassium, cesium, or rubidium containing salt does not increase by more than about 0.03 %, or by more than about 0.05 mV per hour, at an applied current density of 300 mA / cm2or below for more than 100-hour operation. In certain embodiments, the mole fraction of carbon monoxide among all other chemicals produced at the cathode of an MEA cell employing an aqueous sodium, potassium, cesium, or rubidium containing salt does not decrease by more than about 0.1 % per hour, at an applied current density of 300 mA / cm2or lower for more than 100-hour operation.

[0160] Faraday efficiency, which is also sometimes referred to as Faradaic yield, coulombic efficiency or current efficiency, is the efficiency with which charge is transferred in a system facilitating an electrochemical reaction. The use of Faraday’s constant in Faradaic efficiency correlates charge with moles of matter and electrons. Faradaic losses are experienced when electrons or ions participate in unwanted side reactions. These losses appear as heat and / or chemical byproducts.

[0161] Voltage efficiency describes the fraction of energy lost through overpotential or resistance to charge movement in the MEA cell. For an electrolytic cell this is the ratio of a cell's thermodynamic potential divided by the cell's experimental cell voltage, converted to a percentile. Fosses in a cell’s voltage due to overpotentials are described by voltage efficiency. For a given type of electrolysis reaction, electrolytic cells with relatively higher voltage efficiencies have relatively lower overall cell voltage losses due to resistance.

[0162] In certain embodiments, a sodium containing salt such as sodium bicarbonate when used in a bipolar MEA cell with copper catalyst on the cathode produces methane with improved voltage efficiency in proportion with increasing salt concentration. An increase in voltage efficiency by 6.5% was observed when increasing salt concentration from 3mM to 20 mM sodium bicarbonate.

[0163] In certain embodiments, a sodium-containing salt such as sodium bicarbonate whenused in a bipolar MEA cell with copper catalyst on the cathode produces methane with improved voltage efficiency as compared to deionized water. At least about a 30% improvement in initial voltage efficiency and at least about 8x improvement in voltage decay rate was seen when sodium bicarbonate was used as anolyte as compared to deionized water.

[0164] In certain embodiments, a potassium containing salt such as potassium bicarbonate used in an MEA cell having a copper catalyst on a cathode selectively produces ethanol and ethylene over methane during carbon dioxide reduction. By contrast, a sodium containing salt such as sodium bicarbonate when used in an MEA cell having a copper catalyst on a cathode selectively produces methane during carbon dioxide reduction. In MEA cells employing copper reduction catalysts, salts with higher atomic weight cations increase the Faradaic yield of multi-carbon products (e.g., ethylene).Representative Examples of Salts

[0165] In certain embodiments, a salt employed in the reactor has cations that are not ions of transition metals. In certain embodiments, the salt contains a cation that is an alkali metal ion or an alkaline earth metal ion. In certain embodiments, the salt contains a lithium ion, sodium ion, potassium ion, cesium ion, and / or a rubidium ion. In certain embodiments, the salt contains no cations other than sodium, and / or potassium ions. In some implementations, the salt contains only cations that are monovalent such as alkali metal ions.

[0166] In certain embodiments, the salt contains an anion that is hydroxide, bicarbonate, carbonate, perchlorate, phosphate, or sulfate. In some cases, the salt contains an anion that is hydroxide, bicarbonate, carbonate, or sulfate. In certain embodiments, the salt contains no halide ions. In certain embodiments, the salt contains an anion that is produced from the carbon oxide reduction reaction. Examples include carboxylates such as formate, oxalate, and acetate.

[0167] In certain embodiments, the salt is selected from the group including sodium bicarbonate, potassium bicarbonate, potassium sulfate, sodium sulfate, cesium bicarbonate, cesium sulfate, and any combination thereof.

[0168] In some cases, an MEA employs multiple salts or a mixed salt. For example, the MEA may employ multiple cations (e.g., sodium and potassium ions) but only a single anion (e.g., sulfate). In another example, the MEA employs only a single cation (e.g., sodium ions) but multiple anions (e.g., bicarbonate and sulfate). In yet another example, the MEA employs at least two cations and at least two anions. In certain embodiments, the salts include a combination of sodium bicarbonate and potassium bicarbonate. In certain embodiments, the salts include a combination of potassium bicarbonate and potassium phosphate.Delivery of Salt to MEA

[0169] A salt may be delivered to the cell in various ways. In one example, a salt is provided with an MEA as fabricated and / or is provided with a reconstituted MEA. In another example, a salt is provided with a feedstock (a reactant containing composition) to the anode or cathode. In some implementations, water is a reactant at the anode and a salt is provided with the anode reactant. Water supplied to the anode is sometimes termed “anode water.” The anode water may be an aqueous solution that, during operation, is flowed to the anode. In some embodiments, the anode reaction is oxidation of water to produce oxygen. In some embodiments, liquid water containing a salt is delivered to the cathode in any of various ways. For example, the salt may be delivered via flowing a liquid solution to the cathode during operation. The liquid may contain dissolved carbon dioxide or dissolved carbon monoxide. In some cases, aqueous solutions of salt are delivered to the cathode as a mixture of liquid and gas. For example, a salt solution may be sprayed on the MEA.

[0170] Salt-containing solution provided to the MEA directly or via anode water during operation may be prepared in various ways. In some cases, salt-containing solutions are made by dissolving salt directly in water. In some cases, salt-containing solutions are made by passing water through a resin (optionally in a column) that releases salt into the water.Salt Concentration

[0171] In embodiments where salt is provided to the MEA by way of liquid water such as anode water, the salt may be provided at a set concentration. The salt concentration may vary depending upon the materials, MEA configuration, desired reaction, and the particular cathode catalyst employed, as well as the associated carbon oxide reduction reaction.

[0172] In some embodiments, the MEA may be any assembly containing a salt-activated membrane, including but not limited to, anion exchange membranes, polymer electrolyte membranes, or bipolar membranes.

[0173] In some embodiments employing a bipolar membrane MEA, the salt is provided in an aqueous solution at a concentration of about 1 mM to about 30 mM or at a concentration of about 3 mM to about 30 mM. In some embodiments employing a bipolar membrane MEA, the salt is provided at a concentration of about 2 mM to about 15 mM. In some embodiments employing a bipolar membrane MEA, the salt is provided at a concentration of about 0.1 mM to about 30 mM, or about 5 mM to about 10 mM.

[0174] In some embodiments employing a bipolar membrane MEA configured for hydrocarbon production from carbon dioxide, the salt is provided in anode water or other source at a concentration of about 2 mM to about 50 mM. In some MEAs employed in cellsconfigured for methane production from carbon dioxide, the salt is provided in a concentration of about 10 mM to 30 mM. In various implementations, such cells employ a copper catalyst and a salt selected from the group including sodium bicarbonate, potassium bicarbonate, potassium sulfate, sodium sulfate, cesium bicarbonate, cesium sulfate, and any combination thereof. In various embodiments, the salt employed for methane selectivity is sodium bicarbonate, which has been shown to enhance methane to ethylene ratio by at least about 20: 1.

[0175] In certain embodiments employing a bipolar membrane MEA configured for hydrocarbon product generation from a carbon oxide, and particularly carbon dioxide, the salt is provided at a concentration of about 2 mM to 1 M. In some implementations, the salt is potassium bicarbonate, which has been shown to enhance C2-C3 product selectivity over methane by a ratio of about 5:1 compared to sodium bicarbonate, is provided at a concentration of about 100 mM to about 500 mM. In certain embodiments, where the MEA is configured with a copper catalyst as cathode to reduce carbon dioxide to ethylene, the potassium bicarbonate concentration is about 1 mM to 5 mM. In certain embodiments, where the MEA is configured to reduce carbon monoxide to ethylene, the salt concentration, particularly potassium bicarbonate, is about 150 mM to about 250 mM.

[0176] In some embodiments employing an MEA containing only anion-conducting polymer(s), the salt is provided in an aqueous solution at a concentration of about 1 mM to 10 M . In some embodiments employing an MEA containing only anion-conducting polymer, the salt is provided in a concentration of about 100 mM to 5 molar. In certain embodiments employing potassium hydroxide as a salt, the salt concentration is about 50 to 150 mM. In certain embodiments employing potassium bicarbonate as a salt, the salt concentration is about 4 to 10 mM.

[0177] The following concentration ranges are useful for anion conducting polymer only and bipolar cells employing anode water with potassium hydroxide and / or potassium bicarbonate. In certain MEA cells employing potassium hydroxide, the salt concentration is about 10 mM to 15 M. In some MEA cells employing potassium hydroxide, the salt concentration is about 50 to 500 mM. In some MEA cells employing potassium hydroxide, the salt concentration is about 0.5 M to-15 M. In certain MEA cells employing potassium bicarbonate, the salt concentration is about 1 mM to 1 M. In some MEA cells employing potassium bicarbonate, the salt concentration is about 1 to 50 mM. In some MEA cells employing potassium bicarbonate, the salt concentration is about 100 mM to 500 mM.

[0178] The following salt concentration ranges are used, in certain embodiments, employing carbon dioxide as a reactant in an MEA cell:

[0179] Anion conducting polymer only MEA for ethylene production (e.g., copper-containing catalyst): The salt concentration in anode water is about 0.05 M-5 M, or about 0.05 M-l M, or about 0.5 M-l M, or about 0.05 M-0.5 M. In certain embodiments, any of these concentration ranges is used when the salt is potassium hydroxide. In certain embodiments, any of these concentration ranges is used for MEA cells having cathode surface areas of about 25 cm2.

[0180] The following salt concentration ranges are used, in certain embodiments, employing carbon monoxide as a reactant in an MEA cell:

[0181] Anion conducting polymer only MEA for ethylene production (e.g., copper-containing catalyst): The salt concentration in anode water is about 0.05 M-5 M, or about 0.05 M-l M, or about 0.5 M-l M, or about 0.05 M-0.5 M, or about 0.5 M-10 M. In certain embodiments, any of these concentration ranges is used when the salt is potassium hydroxide. In certain embodiments, any of these concentration ranges is used for MEA cells having cathode surface areas of about 25cm2.

[0182] Anion conducting polymer only MEA for methane production (e.g., copper-containing catalyst): The salt concentration in anode water is about 0.05 M-10 M, or about 0.05 M-l M, or about 0.05 M-0.5 M, or about 0.5 M-10 M, or about 0.5 M-l M. In certain embodiments, any of these concentration ranges is used when the salt is potassium hydroxide or sodium hydroxide. In certain embodiments, any of these concentration ranges is used for MEA cells having cathode surface areas of about 25cm2.

[0183] While the salt concentrations provided herein may be appropriate for MEAs of any size, in certain embodiments, they are appropriate for cells employing MEAs having a surface area of about 25 cm2and the listed ranges may be scaled for cells with MEAs having larger surface areas. For example, in some embodiments, the salt concentrations increase with MEA area increases by a ratio of about 3:4. So, for example, if a salt concentration of 2mM is appropriate for a cell having an MEA area of 25 cm2, the concentration may be increased to 6mM for a cell having an MEA area of 100 cm2. As used herein, the area of an MEA is the area of a geometric plane at the MEA surface; it does account for pores or other deviations from planarity at the MEA surface.

[0184] In certain embodiments, the concentration of salt in an MEA, in moles of salt per mass of polymer electrolyte, is between about 1 and 3 mM / g. In certain embodiments, the concentration of salt in the polymer is estimate using conductivity measurements.

[0185] In some implementations, the concentration of any impurity other than introduced salt in anode or cathode water is very low; e.g., on the order of parts per million. This is particularly true of anions that are oxidizable at the anode and cations that are reducible at the cathode. Incertain embodiments, the water containing one or more introduced salts has substantially no other ions other than those of the salt. For example, the water may contain no more than about 100 ppb of any transition metal ion other than any transition metal in the introduced salt. In some cases, the concentration of reducible transition metal ion is no greater than 10 ppb, or no greater than 1 ppb, or no greater than 0.1 ppb. In another example, the water contains no more than about 10 ppm of any halide ion. In another example, the water contains no more than about 10 ppm of any cation other than alkali metal ions and / or alkaline earth metal ions. In another example, the water contains no more than about 10 ppm of any cation other than alkali metal ions. In certain embodiments, the salt-containing water contains no more than about 100 ppm of unintentionally provided ion. In some cases, the salt-containing water contains no more than about 10 ppm of unintentionally provided ion, or no more than about 1 ppm of unintentionally provided ion, or no more than about 0.1 ppm of unintentionally provided ion.

[0186] In certain embodiments, unwanted ions and / or other impurities are removed from water prior to delivery of the water to a carbon dioxide reducing cell. This may be accomplished by purifying water upstream of the anode and / or cathode to which it is delivered. The water may be purified by any of various techniques such as passing the water through a resin column containing a chelating-type resin such as CR11 available from Sigma- Aldrich. Examples of techniques to achieve ultra-high purity water include gross filtration for large particulates, carbon filtration, water softening, reverse osmosis, exposure to ultraviolet (UV) light for TOC and / or bacterial static control, polishing using either ion exchange resins or electrodeionization (EDI) and filtration or ultrafiltration. The specific steps are affected by the starting quality of the water. With certain combinations of steps, it is possible to purify water to the point where it has a resistance of greater than about 18 MOhms. In certain embodiments, a resistance of only about 10 MOhm prior to the deliberate addition of salt is sufficient water purification for CO2 electrolysis.

[0187] The salt concentration values presented herein may define salt concentration in an aqueous solution supplied to an MEA cell. Such solutions include anode water supplied during cell operation, a solution in which an MEA is soaked or otherwise contacted to infuse salt, and the like. The salt concentration may be different in an MEA than in a solution that supplies salt to the MEA. Typically, salt ions will penetrate the MEA from the solution and then move through the MEA via one or more transport mechanisms. In one mechanism, salt ions pass into the MEA via the supply solution. This may be the case when the solution permeates the MEA via pores or other openings in the MEA. Once in the MEA, the solution may move under a pressure gradient. The moving solution carries the salt ions along with it. While the salt ionsare carried in the supply solution, their overall concentration in the MEA may be reduced because they occupy a greater volume: they occupy the volume of the supply solution in addition to the volume of the MEA polymers.

[0188] Salt ions in the solution may move independently of the bulk solution under the influence of a salt concentration gradient (diffusion or osmosis) or under the influence of an electric field (migration). These transport phenomena may also modify the salt concentration within the MEA. Independently of movement within the supply solution, salt ions may move by ionic conduction through the conductive polymers of the MEA. For example, salt cations may move by ionic conduction in the polymer matrix of a cation exchange membrane such as a sulfonated tetrafluoroethylene. And salt anions may move by ionic conduction through the matrix of an anion exchange membrane. The movement of salt ions in such polymer matrixes is sometimes referred to hopping, with the salt ions hopping between adjacent charged sites within a polymer matrix. During operation of an MEA cell, the salt ions within the polymer matrixes have their own concentrations that contribute to the overall salt or salt ion concentration in the MEA.

[0189] Due to the above factors and possibly other factors, the salt concentration in the MEA may be different from the salt concentration in the supply solution. While the salt concentration values presented herein typically represent the salt concentrations within the supply solution, before it penetrates the MEA, the values may also represent the concentration within an MEA. To the extent that the values represent concentrations within an MEA, they should be considered average values throughout the MEA. Note that salt ions may have different molar concentrations than their source salts. For example, a 1 M solution of sodium sulfate may, when fully dissociated, be viewed as providing a 2 M solution of sodium ions.Delivery of Salt via the MEA

[0190] In certain embodiments, salt is provided, at least in part, via pre-operation introduction to one or more components of the MEA. For example, the PEM, cathode buffer layer, anode buffer layer, anode catalyst layer, cathode catalyst layer, or any combination thereof may be pre-loaded with salt. The pre-loading may be performed before, during, or after assembly of individual MEA layers into an MEA stack. In some implementations, before the assembly, the pre-loading is achieved by soaking different layers of MEA in salt-containing solutions at various preferred concentrations. In some implementations, during the assembly, the pre- loading is achieved by adding droplets of salt-containing solutions onto different layers of MEAs. In some implementations, after the assembly, the pre-loading is achieved by circulating salt-containing solutions at the anode and / or the cathode compartment.

[0191] In certain embodiments, salt is introduced to an MEA after the MEA has operated for a time in a carbon oxide reduction cell. In some cases, after a certain amount of usage, the MEA is taken out of service and exposed to a composition that introduces salt into the polymers of the MEA. This may be accomplished, for example, by adding salt to the anode water or by putting salt-containing water through the cathode of the cell.Remove Salt from MEA Cell

[0192] In certain embodiments, salts can precipitate or otherwise come out of solution and accumulate in certain locations within the cell. For example, salts may deposit in a cell’s flow field and / or MEA layers and ultimately foul the cell.

[0193] To address this concern or for other reasons, the cell may be periodically taken off line and exposed to a flow of water (e.g., deionized water) under hydrodynamic conditions (flow velocity, pressure, and the like) that purge solid salt from the flow field or other structure where it has formed. In some cases, deionized water is flowed through the cell under thermodynamic conditions that facilitate dissolution of the solid salt.Management of Salt Concentration and. Water Delivery in MEA Cells

[0194] As mentioned, salt may be provided to an MEA from various sources including anode water and preloaded MEA polymer layers. Salts provided to an MEA cell can become depleted over the course of the cell’s operation. This may happen even when salt-containing anode water is recycled to the MEA. Various mechanisms may account for this loss. For example, salt from anode water may be taken up by one or more MEA components such as a PEM or other cation exchange polymer layer. Further, some salt may move by diffusion, migration, and / or osmosis from a region of high concentration (anode) to a region of lower concentration (cathode). The anode water itself — not just its salt content — may move due to permeation of the anode water from the anode to the cathode where it is swept away by flowing gaseous carbon oxide.

[0195] Various mechanisms may be employed to manage salt concentration during operation of an MEA cell. For example, anode water may be treated to (a) add salt, (b) remove impurities, and / or (c) add purified water. Such treatment may be accomplished by dosing concentrated salt solutions and / or purified water to anode water in an anode water reservoir. Removing impurities may be accomplished by filtration and / or treatment with ion exchange resins.

[0196] Various mechanisms may be employed to manage anode water depletion during operation of an MEA cell. One way is to capture the water that leaves the anode and recirculate the water back to an anode water inlet. Another way is by recycling water recovered in the cathode product stream. In some implementations, the cathode water includes salts introducedvia the anode water.

[0197] Returning to FIG. 1, during operation the anode subsystem may provide water or other reactant to the anode of reactor 103, where it at least partially reacts to produce an oxidation product such as oxygen. The product along with unreacted anode feed material is provided in a reduction reactor outlet stream. Not shown in FIG. 1 is an optional separation component that may be provided on the path of the anode outlet stream and configured to concentrate or separate the oxidation product from the anode product stream.

[0198] Other control features may be included in system 100. For example, a temperature controller may be configured to heat and / or cool the carbon oxide reduction reactor 103 at appropriate points during its operation. In the depicted embodiment, a temperature controller 105 is configured to heat and / or cool anode water provided to the anode water recirculation loop. For example, the temperature controller 105 may include or be coupled to a heater and / or cooler that may heat or cool water in anode water reservoir 119 and / or water in reservoir 121. In some embodiments, system 100 includes a temperature controller configured to directly heat and / or cool a component other than an anode water component. Examples of such other components in the cell or stack and the carbon oxide flowing to the cathode.

[0199] Depending upon the phase of the electrochemical operation, including whether current is paused to carbon oxide reduction reactor 103, certain components of system 100 may operate to control non-electrical operations. For example, system 100 may be configured to adjust the flow rate of carbon oxide to the cathode and / or the flow rate of anode feed material to the anode of reactor 103. Components that may be controlled for this purpose may include carbon oxide flow controller 113 and anode water controller 111.

[0200] In addition, depending upon the phase of the electrochemical operation including whether current is paused, certain components of system 100 may operate to control the composition of the carbon oxide feed stream and / or the anode feed stream. For example, water reservoir 121 and / or anode water additives source 123 may be controlled to adjust the composition of the anode feed stream. In some cases, additives source 123 may be configured to adjust the concentration of one or more solutes such as one or more salts in an aqueous anode feed stream.

[0201] In some cases, a temperature controller such controller 105 is configured to adjust the temperature of one or more components of system 100 based on a phase of operation. For example, the temperature of cell 103 may be increased or decreased during break-in, a current pause in normal operation, and / or storage.

[0202] In some embodiments, a carbon oxide electrolytic reduction system is configured tofacilitate removal of a reduction cell from other system components. This may be useful with the cell needs to be removed for storage, maintenance, refurbishment, etc. In the depicted embodiments, isolation valves 125a and 125b are configured to block fluidic communication of cell 103 to a source of carbon oxide to the cathode and backpressure controller 115, respectively. Additionally, isolation valves 125c and 125d are configured to block fluidic communication of cell 103 to anode water inlet and outlet, respectively.

[0203] The carbon oxide reduction reactor 103 may also operate under the control of one or more electrical power sources and associated controllers. See block 133. Electrical power source and controller 133 may be programmed or otherwise configured to control current supplied to and / or to control voltage applied to the electrodes in reduction reactor 103. The current and / or voltage may be controlled to execute the current schedules and / or current profiles described elsewhere herein. For example, electrical power source and controller 133 may be configured to periodically pause current applied to the anode and / or cathode of reduction reactor 103. Any of the current profiles described herein may be programmed into power source and controller 133.

[0204] In certain embodiments, electric power source and controller 133 performs some but not all the operations necessary to implement desired current schedules and / or profiles in the carbon oxide reduction reactor 103. A system operator or other responsible individual may act in conjunction with electrical power source and controller 133 to fully define the schedules and / or profiles of current applied to reduction reactor 103. For example, an operator may institute one or more current pauses outside the set of current pauses programmed into power source and controller 133.

[0205] In certain embodiments, the electrical power source and controller acts in concert with one or more other controllers or control mechanisms associated with other components of system 100. For example, electrical power source and controller 133 may act in concert with controllers for controlling the delivery of carbon oxide to the cathode, the delivery of anode water to the anode, the addition of pure water or additives to the anode water, and any combination of these features. In some implementations, one or more controllers are configured to control or operate in concert to control any combination of the following functions: applying current and / or voltage to reduction cell 103, controlling backpressure (e.g., via backpressure controller 115), supplying purge gas (e.g., using purge gas component 117), delivering carbon oxide (e.g., via carbon oxide flow controller 113), humidifying carbon oxide in a cathode feed stream (e.g., via humidifier 104), flow of anode water to and / or from the anode (e.g., via anode water flow controller 111), and anode water composition (e.g., via anodewater source 105, pure water reservoir 121, and / or anode water additives component 123).

[0206] In the depicted embodiment, a voltage monitoring system 134 is employed to determine the voltage across an anode and cathode of an MEA cell or across any two electrodes of a cell stack, e.g., determining the voltage across all cells in a multi-cell stack. The voltage determined in this way can be used to control the cell voltage during a current pause, inform the duration of a pause, etc. In certain embodiments, voltage monitoring system 134 is configured to work in concert with power supply 133 to cause reduction cell 103 to remain within a specified voltage range. For example, power supply 133 may be configured to apply current and / or voltage to the electrodes of reduction cell 103 in a way that maintains the cell voltage within a specified range during a current pause. If, for example during a current pause, the cell’s open circuit voltage deviates from a defined range (as determined by voltage monitoring system 134), power supply may be configured to apply current or voltage to the electrodes to maintain the cell voltage within the specified range.

[0207] A condition that may trigger protection mode is loss of power to the electrolyzer. Under such a condition, it may be desirable to apply a small current to the electrolyzer while power is otherwise unavailable. To accomplish this, some electrolyzer systems include an uninterruptible power supply (UPS) which may include a power source such as a battery or battery pack having a capacity sufficient to provide at least limited amounts of current to the electrolyzer. As indicated, supplying such current may mitigate problems or potential problems created by unforeseen interruptions such as a power outage.

[0208] In some embodiments, a UPS is directly integrated with a carbon oxide electrolyzer or a group of electrolyzers. Some industrial scale carbon oxide electrolyzer systems may employ a dedicated UPS. Examples of industrial scale electrolyzers include those configured to consume at least about 100 kg of carbon dioxide per day. In some cases, such industrial scale carbon oxide electrolysis systems can operate off the power of about 100 kW or greater.

[0209] An electrolytic carbon oxide reduction system such as that depicted in FIG. 1 may employ a control system that includes one or more controllers and one or more controllable components such as pumps, sensors, dispensers, valves, and power supplies. Examples of sensors include pressure sensors, temperature sensors, flow sensors, conductivity sensors, voltmeters, ammeters, electrolyte composition sensors including electrochemical instrumentation, chromatography systems, optical sensors such as absorbance measuring tools, and the like. Such sensors may be coupled to inlets and / or outlets of an MEA cell (e.g., in a flow field), in a reservoir for holding anode water, pure water, salt solution, etc., and / or other components of an electrolytic carbon oxide reduction system.

[0210] Among the various functions that may be controlled by one or more controllers are: applying current and / or voltage to a carbon oxide reduction cell, controlling backpressure on an outlet from a cathode on such cell, supplying purge gas to a cathode inlet, delivering carbon oxide to the cathode inlet, humidifying carbon oxide in a cathode feed stream, flowing anode water to and / or from the anode, and controller anode feed composition. Any one or more of these functions may have a dedicated controller for controlling its function alone. Any two or more of these functions may share a controller. In some embodiments, a hierarchy of controllers is employed, with at least one master controller providing instructions to two or more component controllers. For example, a system may comprise a master controller configured to provide high level control instructions to (i) a power supply to a carbon oxide reduction cell, (ii) a cathode feed stream flow controller, and (iii) an anode feed stream flow controller. For example, a programmable logic controller (PLC) may be used to control individual components of the system.

[0211] In certain embodiments, a control system is configured to apply current to a carbon oxide reduction cell comprising an MEA in accordance with a current schedule, which may have any of the characteristics described herein. For example, the current schedule may provide periodic pauses in the applied current. In some cases, the control system provides the current pauses with defined profiles such as ramps and / or step changes as described herein.

[0212] In certain embodiments, a control system is configured to control the flow rate of one or more feed streams (e.g., a cathode feed stream such as a carbon oxide flow and an anode feed stream) in concert with a current schedule. For example, the flow of carbon oxide or a purge gas may be turned on, turned off, or otherwise adjusted when current applied to an MEA cell is paused.

[0213] In certain embodiments, a control system may be configured to implement a recovery sequence as described herein. Such control system may be configured to pause or reduce current, flow a recovery gas, flow water or other liquid, dry the cathode, resume normal operation, or any combination thereof. The controller may be configured to control the initiation of a recovery sequence, control the duration of any operation in a recovery sequence, etc.

[0214] A controller may include any number of processors and / or memory devices. The controller may contain control logic such software or firmware and / or may execute instructions provided from another source. A controller may be integrated with electronics for controlling operation the electrolytic cell before, during, and after reducing a carbon oxide. The controller may control various components or subparts of one or multiple electrolytic carbon oxidereduction systems. The controller, depending on the processing requirements and / or the type of system, may be programmed to control any of the processes disclosed herein, such as delivery of gases, temperature settings (e.g., heating and / or cooling), pressure settings, power settings (e.g., electrical voltage and / or current delivered to electrodes of an MEA cell), liquid flow rate settings, fluid delivery settings, and dosing of purified water and / or salt solution. These controlled processes may be connected to or interfaced with one or more systems that work in concert with the electrolytic carbon oxide reduction system.

[0215] In various embodiments, a controller comprises electronics having various integrated circuits, logic, memory, and / or software that receive instructions, issue instructions, control operations described herein. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and / or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a process on one or more components of an electrolytic carbon oxide reduction system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during generation of a particular reduction product such as carbon monoxide, hydrocarbons, and / or other organic compounds.

[0216] The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may utilize instructions stored remotely (e.g., in the “cloud”) and / or execute remotely. The computer may enable remote access to the system to monitor current progress of electrolysis operations, examine a history of past electrolysis operations, examine trends or performance metrics from a plurality of electrolysis operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the internet. The remote computer may include a user interface that enables entry or programming of parameters and / or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations.

[0217] The controller may be distributed, such as by comprising one or more discretecontrollers that are networked together and working towards a common purpose, such as applying current to an MEA cell and other process controls described herein. An example of a distributed control system for such purposes includes one or more processors on a system for electrolytically reducing a carbon oxide and one or more processors located remotely (such as at the platform level or as part of a remote computer) that combine to control a process.

[0218] Controllers and any of various associated computational elements including processors, memory, instructions, routines, models, or other components are sometimes described or claimed as “configured to” perform a task or tasks. In such contexts, the phrase “configured to” is used to connote structure by indicating that the component includes structure (e.g., stored instructions, circuitry, etc.) that performs a task or tasks during operation. As such, a controller and / or associated component can be said to be configured to perform the task even when the specified component is not necessarily currently operational (e.g., is not on).

[0219] Controllers and other components that are “configured to” perform an operation may be implemented as hardware — for example, circuits, memory storing program instructions executable to implement the operation, etc. Additionally, controllers and other components “configured to” perform an operation may be implemented as hardware that is manipulated by software and / or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the recited task(s). Additionally, “configured to” can refer to one or more memories or memory elements storing computer executable instructions for performing the recited task(s). Such memory elements may include memory on a computer chip having processing logic.Method of Operating an Electrochemical Cell with Conductivity Measurement

[0220] FIG. 3 is a process flow diagram for a method 300 of operating an electrolyzer for carbon oxide reduction in accordance with certain disclosed embodiments.

[0221] As represented by block 301, the first step is to provide an electrochemical cell having a membrane electrode assembly, where the membrane electrode assembly includes a cathode, an anode, and an anion exchange membrane disposed between the cathode and the anode.

[0222] At block 303, an anolyte solution is introduced into the electrochemical cell such that the anolyte solution contacts the anion exchange membrane. The anolyte solution includes a salt and is supplied from an anolyte reservoir. Suitable salts and salt concentrations are as described above. In some embodiments, the salts may be alkali metal ions. In some embodiments, the salt is an anion including, but not limited to, phosphate, sulfate, carbonate, bicarbonate, and / or hydroxide. In some embodiments, the salt comprises ions of potassium, sodium, cesium, rubidium, or a combination thereof. In some embodiments, the salt comprisesmagnesium carbonate, calcium carbonate, cesium carbonate, or potassium carbonate. The anolyte solution comprises about 100 mM or less of a salt in certain embodiments.

[0223] At block 305, the conductivity of the anolyte solution is measured. The terms “measuring”, “measure”, or “measurement” as used herein includes a single point measurement or continual measurement. Conductivity may be assessed on a continuous basis, or by taking readings at specified intervals of time. Conductivity may be measured at the membrane electrode assembly, at the anode flow field, within tubing of the electrolyzer, at the anolyte salt solution reservoir, or combinations thereof. The conductivity measurement device is described in further detail below with reference to FIG. 6.

[0224] Returning to FIG. 3, at block 307, a gas of a carbon oxide is supplied to the cathode of the MEA. The gas may also contain water vapor in certain embodiments. The carbon oxide may be a humidified carbon oxide in certain embodiments.

[0225] At block 309, a current is applied to the MEA to reduce a carbon oxide and produce a carbon-containing product. The carbon-containing reduction product may be carbon monoxide, a hydrocarbon, or an organic oxygen-containing compound. In some embodiments, a conductivity of the anolyte solution less than or equal to a desired setpoint conductivity may be detected before applying a current to the membrane electrode assembly.

[0226] A desired setpoint conductivity will be determined by an operator in accordance with the particular inputs, process conditions, and desired products. The desired setpoint conductivity may be set by the concentration of the electrolyte (i.e., anolyte salt solution) in certain embodiments. Suitable anolyte concentrations include, but are not limited to, 0.01 M to 1 M bicarbonate or hydroxide salts; having conductivity of from about 10 uS / cm to about 20,000 uS / cm.

[0227] If an elevated conductivity is observed as described at block 305 above after applying the current at block 309; an anolyte restoration operation can be utilized to return the electrochemical cell to normal operating conditions. Without wishing to be bound by theory, it is believed that the elevated conductivity indicates that residual salt has leached into the anolyte salt solution from the anion exchange membrane. For example, residual salt present in the anion exchange membrane after undergoing an activation procedure may have leached into the anolyte salt solution.

[0228] The anolyte restoration operation may be one or more of the following: (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt in the anolyte solution, and (iii) reducing the first current density to a second current density, until conductivity of the anolyte solution is reduced to less than or equal to the desired setpoint conductivity.

[0229] When the anolyte restoration operation is to replace the anolyte solution with water, it is water which is pure or deionized water, free of additives. Water is supplied to the anolyte salt solution reservoir from a water reservoir. In some embodiments replacing the anolyte solution with water includes circulating the water from the anolyte reservoir through the electrochemical cell; and delivering the anolyte solution from the electrochemical cell to the anolyte reservoir such that a concentration of the anolyte solution is diluted by the water provided to the anolyte reservoir. Put another way, although the contents of the anolyte salt solution reservoir may be replaced with water, the electrochemical cell and associated tubing that delivers the anolyte salt solution to and from the electrochemical cell may still contain the anolyte salt solution. Accordingly, as the anolyte salt solution circulates back to the anolyte salt solution reservoir, which contains water, the anolyte salt solution may become diluted as the water from the anolyte salt solution reservoir begins to circulate.

[0230] When the anolyte restoration operation is to lower the concentration of the salt in the anolyte solution, it may entail lowering the concentration of the salt in the anolyte solution within the anolyte reservoir to a salt concentration that is greater than zero and less than 100 mM in certain embodiments. The concentration may be lowered by adding water from the water reservoir to the anolyte salt solution reservoir.

[0231] When the anolyte restoration operation is to decrease the first current density to a second current density, it may be accomplished all at once, or incrementally. If incrementally, the current density may be adjusted by continuously ramping the current density down. If incrementally, the current density may be modified in a stepwise fashion, with changes in 5-25 mA / cm2increments. In some embodiments, the first current density is greater than about 10 mA / cm2and the second current density is about 5 mA / cm2or less.

[0232] In various embodiments, decreasing the first current density to the second current density may be employed as at least a portion of the anolyte restoration operation when the electrochemical cell has already begun receiving the first current density (e.g., the electrochemical cell has been running for a period of time). In such embodiments, lowering the first current density to the second current density does not impact the conductivity of the anolyte salt solution. Rather, lowering the first current density to the second current density can decrease a rate of electrochemically-promoted salt precipitation while further action is taken.

[0233] A single anolyte restoration operation may be utilized, or more than one anolyte restoration operation may be utilized such as current density adjustment with concomitant lowering of salt concentration.

[0234] If a conductivity of the anolyte solution is detected to be less than or equal to the desired setpoint conductivity as described in block 305 after the anolyte restoration operation has been executed; the current applied can be returned to the first current density in response to the detection of the conductivity of the anolyte solution being less than or equal to the desired setpoint conductivity after the anolyte restoration operation has been executed.

[0235] Method 300 may be performed independent of temperature considerations.

[0236] Operating an electrochemical cell for carbon oxide reduction comprises, consists of, or consists essentially of the steps described herein in certain embodiments.Method for Preparing an Electrochemical Cell

[0237] FIG. 4 is a process flow diagram for a method 400 of preparing an electrochemical cell in accordance with certain disclosed embodiments. Preparing an electrochemical cell for carbon oxide reduction comprises, consists of, or consists essentially of activating an anion exchange membrane in certain embodiments. Once activated, the membrane allows the transport of the desired anion of interest (i.e. bicarbonate or hydroxide). The activation process changes the functional mobile group of the AEM to bicarbonate or hydroxide depending on the functional activation solution. If the AEM is not activated, then no transport of charged moieties will occur.

[0238] An AEM is activated in a concentrated solution, as represented at block 401. It may be activated in a first basic solution with a salt that will also be used for the anolyte salt solution, such as KOH in some embodiments. In that regard, a two-step activation process is utilized where 1) the AEM is soaked for about 24 hours in a 0.5 to 2 M solution of a first electrolyte, such as a 1 M KOH solution, until it detaches from its liner; after which point the liner-free AEM is soaked in the 1 M KOH solution for about 6-12 more hours; and 2) after soaking, the AEMis rinsed with water. The rinse water is pure or deionized water, free of additives. In some embodiments, the first electrolyte is potassium hydroxide, calcium hydroxide, sodium hydroxide, cesium hydroxide, rubidium hydroxide, or another hydroxide-containing salt.

[0239] However, if the rinsing is not conducted for a sufficient length of time, the strong base solution may not be adequately removed for most effective electrochemical cell operation. Hence, the step 2) water rinse for a period of from about 1 to about 48 hours after the soak is advantageous, as represented at block 403.

[0240] When an electrolyte that is different than the first electrolyte is to be utilized for operation of the electrochemical cell, activation of the anion exchange membrane, as represented at block 401, includes the following steps: 1) the AEM is soaked for about 24 hours in a 0.5 to 2 M solution of a first electrolyte, such as a 1 M KOH solution, until it detachesfrom its liner; after which point the liner-free AEM is soaked in the 1 M KOH solution for about 6-12 more hours; 2) the AEM is rinsed with water for a short period of time (e.g., about 1 minute); 3) the anion exchange membrane is soaked for about 48 to 72 hours in a 0.5 to 2 M solution of a second electrolyte, such as a bicarbonate-based electrolyte , and 4) after soaking in the second electrolyte, the AEM is rinsed with water for between about 1 hour and about 48 hours, as represented by block 403. In some embodiments, the second electrolyte may be a carbonate-based salt or a bicarbonate -based salt. For example, the second electrolyte may be, but is not limited to, magnesium carbonate, calcium carbonate, potassium bicarbonate, sodium bicarbonate, cesium bicarbonate, or rubidium bicarbonate.

[0241] After the two-step or the four- step activation of the anion exchange membrane has been completed as described above, the electrochemical cell is assembled as represented at block 405.

[0242] Method 400 may be performed independent of temperature considerations. The method 400 may be performed at a temperature of from about 20- 50 °C in certain embodiments.Method for Activating an Electrochemical Cell as Refined by Conductivity Measurement

[0243] FIG. 5 is a process flow diagram for a method 500 of activating an electrochemical cell in accordance with certain disclosed embodiments. In order to begin operation of an assembled electrochemical cell, certain start-up steps must be performed which may be referred to as activation procedures.

[0244] As represented by block 501, the first step is to provide an electrochemical cell having a membrane electrode assembly, where the membrane electrode assembly includes a cathode, an anode, and an anion exchange membrane disposed between the cathode and the anode and in contact with an anolyte solution, where the anolyte solution comprises about 100 mM or less of a salt and where the anolyte solution is supplied from an anolyte reservoir.

[0245] The membrane electrode assembly includes an activated anion exchange membrane in certain embodiments. The anion exchange membrane may be activated by soaking an anion exchange membrane in an 0.5 to 2 M solution of a first electrolyte for about 1 to 48 hours; rinsing the anion exchange membrane with water; soaking the anion exchange membrane for about 1 to 72 hours in an 0.5 to 2 M of a second electrolyte; and then rinsing the anion exchange membrane with water for between about 1 hour and about 48 hours as described in greater detail with reference to FIG. 4 above.

[0246] Returning to FIG. 5, a current is then applied to the electrochemical cell as represented by block 503. In some embodiments, the current density is greater than about 10 mA / cm2.

[0247] A conventional activation procedure may involve only the steps represented by blocks501 and 503. However, to have better control over the properties of the anolyte solution, monitoring conductivity and making adjustments as a result of changes in conductivity or a conductivity above or below a target value as indicated in the additional activation steps represented by blocks 505-509 is advantageous.

[0248] Furthermore, it has been observed that anolyte conductivity may spike upon initial connection of an electrochemical cell for operation to a power source, even prior to application of current. Accordingly, the anolyte seems to concentrate after activation of the anion exchange membrane. Without wishing to be bound by theory, it is believed that residual salts from the concentrated electrolyte used in AEM activation exit the AEM during the initial flow of anolyte as the cell is prepared for operation, thereby providing the increased salt concentration to the anolyte and causing an observable increase in anolyte conductivity even before current is applied.

[0249] At block 505, the conductivity of the anolyte salt solution is measured. The terms “measuring”, “measure” or “measurement” as used herein includes a single point measurement or continual measurement. Conductivity may be measured in line using tubing that fluidically connects the anolyte salt solution reservoir to the MEA, within the electrolyzer, at the anolyte salt solution reservoir, or at combinations of these points. The conductivity measurement device is described in further detail below with reference to FIG. 6.

[0250] Returning to FIG. 5, at block 507 when the conductivity measured at block 505 is greater than a desired setpoint conductivity, the elevated conductivity indicates that there are certain process conditions which should be addressed and adjusted. Without wishing to be bound by theory, it is believed that the elevated conductivity indicates that residual salt has leached into the anolyte salt solution from the anion exchange membrane.

[0251] In some embodiments, an elevated conductivity is indicated by a conductivity which is 10% or more above the desired setpoint conductivity. Monitoring for such changes and making adjustments protects the electrochemical cell and potentially prolongs the lifespan of the electrochemical cell; as conductivity can suddenly and rapidly increase from about 400 pS / cm to 1,000 pS / cm and may even go as high as 8,000 or 10,000 pS / cm. The desired setpoint conductivity is determined by an operator and dictated by the specific materials, electrochemical components, and desired products. In some embodiments, the desired setpoint conductivity may be equivalent to the conductivity of a 0.1 M KHCO3 solution. In some embodiments, the desired setpoint conductivity is a number within the range of 100 to 500 pS / cm. In certain embodiments, the desired setpoint conductivity is 400 pS / cm.

[0252] At block 509, once an elevated conductivity is observed as described with reference toblock 507 above, adjustment or adjustments to the system are imperative. The adjustments may be one or more of the following: (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt in the anolyte solution, and (iii) reducing the first current density to a second current density, until conductivity of the anolyte solution is reduced to less than or equal to the desired setpoint conductivity.

[0253] When the adjustment is to replace the anolyte solution with water, it is water which is pure or deionized water, free of additives. Water is supplied to the anolyte salt solution reservoir from a water reservoir.

[0254] When the adjustment is to lower the concentration of the salt in the anolyte solution, it may entail lowering the concentration of the salt in the anolyte solution within the anolyte reservoir to a salt concentration that is greater than zero and less than 100 mM in certain embodiments. The concentration may be lowered by adding water from the water reservoir to the anolyte salt solution reservoir.

[0255] When the adjustment is to reduce the first current density to a second current density, it may be accomplished all at once, or incrementally. If incrementally, the current density may be adjusted by continuously ramping the current up. If incrementally, the current density may be modified in a stepwise fashion, with changes in 5-25 mA / cm2increments. In some embodiments, the first current density is greater than about 10 mA / cm2and the second current density is about 5 mA / cm2or less.

[0256] In various embodiments, decreasing the first current density to the second current density may be employed as at least a portion of the anolyte restoration operation when the electrochemical cell has already begun receiving the first current density (e.g., the electrochemical cell has been running for a period of time). In such embodiments, lowering the first current density to the second current density does not impact the conductivity of the anolyte salt solution. Rather, lowering the first current density to the second current density can decrease a rate of electrochemically-promoted salt precipitation while further action is taken.

[0257] A single adjustment operation may be utilized, or more than one adjustment operations may be utilized such as current density adjustment with concomitant lowering of salt concentration.

[0258] Once the adjustment operation has been completed, as indicated by a conductivity which has been reduced to less than or equal to the desired setpoint conductivity, the electrochemical cell is activated and fully ready to operate efficiently.

[0259] Method 500 may be performed independent of temperature considerations. Method500 may also be useful for electrochemical cells having gas diffusion electrodes including ionomers, when the ionomer is deposited in an inactive form. Issues arising from activation of the ionomer may be advantageously monitored and addressed with the system 600 further described below with respect to FIG. 6.Apparatus

[0260] FIG. 6 depicts a system 600 for measuring conductivity before or during the operation of a carbon oxide reduction reactor that may include an electrochemical cell (electrolyzer) 603 comprising a MEA; and performing anolyte salt solution restoration or adjustment operations in accordance with certain disclosed embodiments. In system 600, electrolyzer 603 is in fluid communication with anolyte salt solution reservoir 605 via anolyte salt solution recirculation loop 607. Electrolyzer 603 ’s MEA is similar to MEA 103 as described above with reference to FIG. 1. Returning to FIG. 6, valves 609 and 611 may be open or closed as necessary to regulate anolyte salt solution flow into and out of electrolyzer 603. Pump 613 is configured to circulate the anolyte salt solution through recirculation loop 607 and into electrolyzer 603.

[0261] Anolyte salt solution reservoir 605 is supplied by salt unit 615. Salt unit 615 may be a hopper in certain embodiments for containing the salts described above. Anolyte salt solution reservoir 605 is also supplied by water reservoir 617. Water reservoir 617 is fluidly connected to anolyte salt solution reservoir 605 via conduit 619. The flow of water from water reservoir 617 to anolyte salt solution reservoir 605 is regulated by valve 621. Water supplied from water reservoir 617 through conduit 619 may be utilized to either completely replace the anolyte salt solution, or dilute the anolyte salt solution; thereby performing an adjustment operation or an anolyte salt solution restoration operation as described above.

[0262] Before water supplied from water reservoir 617 through conduit 619 is utilized to completely replace the anolyte salt solution, the anolyte salt solution reservoir 605 can be drained via conduit 623. Pump 613 may also be utilized to pump out anolyte salt solution in recirculation loop 607 so that it can be replaced with water. The draining of anolyte salt solution reservoir 605 is regulated through valve 625. The concentrated anolyte salt solution 627 drained from the anolyte salt solution reservoir 605 may be recovered and processed for re-use. In some embodiments, a separate drain pump (not shown) drains anolyte salt solution from the MEA.

[0263] Electrolyzer 603 is connected to power source and controller 631, similar to power source and controller 133 described above with reference to FIG. 1. Returning to FIG. 6, conductivity measurement device 629 is utilized to measure the conductivity of the anolyte salt solution flowing through electrolyzer 603. The conductivity measurement device 629 isconnected to power source and controller 631 by connection 637. Measurements of conductivity may be sampled a) at the electrolyzer 603 with a probe connected to electrolyzer 603 via flow tubing 639; b) by sampling the anolyte salt solution incoming to electrolyzer 603 with a probe connected to electrolyzer 603 via flow tubing 641; c) by sampling the anolyte salt solution in the anolyte salt solution reservoir 605 with a probe connected to electrolyzer 603 via flow tubing 643; or d) by sampling at one or more of the points a) - c). Moreover, measurements of conductivity may also be sampled at valve 609 or between valve 609 and electrolyzer 603 (not shown).

[0264] The device may include one or more sensors in contact with the anolyte salt solution. Such sensors may include two wire leads proximal to one another and placed in the flow path of the anolyte salt solution. A primary signal in the form of a voltage is applied to the leads from power supply 631. When the anolyte salt solution comes into contact with both leads, a circuit is completed through the anolyte salt solution to allow a secondary signal to travel back to a controller or readout device (not shown). Conductivity measurements of the anolyte salt solution in the MEA with conductivity measurement device 629 may be utilized to determine that an adjustment operation or an anolyte salt solution restoration operation as described above should be performed.

[0265] Alternatively, or in addition to measuring conductivity in the electrolyzer 603, conductivity measurement device 629 may measure conductivity of the anolyte salt solution in the anolyte salt solution reservoir 605.

[0266] System 600 may also include one or more controllers (not shown) configured to cause the electrochemical cell to perform adjustment operations or anolyte salt solution operations.

[0267] The electrolyzer 603 is connected to a cathode subsystem at points 633 and 635; the cathode subsystem (not shown) is as described above with reference to FIG. 1.Conclusion

[0268] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.

[0269] Although omitted for conciseness, embodiments of the system and / or method can include every combination and permutation of the various system components and the various method processes, wherein one or more instances of the method and / or processes describedherein can be performed asynchronously (e.g., sequentially), concurrently (e.g., in parallel), or in any other suitable order by and / or using one or more instances of the systems, elements, and / or entities described herein.

[0270] As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A method of operating an electrolyzer for carbon oxide reduction comprising: a) providing an electrochemical cell having a membrane electrode assembly, the membrane electrode assembly comprising: i) a cathode, ii) an anode, and iii) an anion exchange membrane disposed between the cathode and the anode; b) introducing an anolyte solution to the electrochemical cell such that the anolyte solution contacts the anion exchange membrane, the anolyte solution comprising a salt and being supplied from an anolyte reservoir; c) measuring conductivity of the anolyte solution; d) inletting a gas comprising a carbon oxide to the cathode of the membrane electrode assembly; and e) applying a current of a first current density to the membrane electrode assembly to thereby reduce the carbon oxide and produce a carbon-containing reduction product.

2. The method of claim 1, further comprising: detecting that the conductivity of the anolyte solution is less than or equal to a desired setpoint conductivity prior to initiating step e) of applying the current to the membrane electrode assembly.

3. The method of claim 1, further comprising: detecting that the conductivity of the anolyte solution is greater than a desired setpoint conductivity after initiating step e), wherein the conductivity of the anolyte solution is an elevated conductivity; and performing an anolyte restoration operation in response to the detection of the elevated conductivity, the anolyte restoration operation comprising one or more operations selected from (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt of the anolyte solution within the anolyte reservoir, and (iii) reducing the first current density to a second current density after step e).

4. The method of claim 3, wherein the anolyte restoration operation comprises (i) replacing the anolyte solution with water within the anolyte reservoir.

5. The method of claim 4, further comprising: circulating the water from the anolyte reservoir through the electrochemical cell; and delivering the anolyte solution from the electrochemical cell to the anolyte reservoir such that a concentration of the anolyte solution is diluted by the water provided to the anolyte reservoir.

6. The method of claim 3, wherein the anolyte restoration operation comprises (ii) lowering the concentration of the salt of the anolyte solution to a salt concentration that is greater than zero and less than 100 mM.

7. The method of claim 3, wherein the anolyte restoration operation comprises (iii) reducing the first current density to a second current density after step e).

8. The method of claim 7, wherein the first current density is greater than about 10 mA / cm2and wherein the second current density is about 5 mA / cm2or less.

9. The method of claim 7, wherein reducing the first current density to the second current density is accomplished all at once.

10. The method of claim 7, wherein reducing the first current density to the second current density is accomplished in multiple increments.

11. The method of claim 7, wherein reducing the first current density to the second current density is accomplished in a continuous ramp.

12. The method of any one of claims 7-11, further comprising: detecting that the conductivity of the anolyte solution is less than or equal to the desired setpoint conductivity after the anolyte restoration operation has been executed; and returning the current applied at step e) to the first current density in response to the detection of the conductivity of the anolyte solution being less than or equal to the desired setpoint conductivity after the anolyte restoration operation has been executed.

13. The method of claim 12, wherein returning the current applied at step e) to the first current density is accomplished all at once.

14. The method of claim 12, wherein returning the current applied at step e) to the first current density is accomplished in incremental current adjustments.

15. The method of claim 12, wherein returning the current applied at step e) to the first current density is accomplished by a continuous current ramp.

16. The method of claim 1, wherein step c) of measuring the conductivity of the anolyte solution is performed in the anolyte reservoir.

17. The method of claim 3, wherein the elevated conductivity is at least about 10% greater in magnitude than the desired setpoint conductivity.

18. The method of claim 1, wherein the anolyte solution comprises about 100 mM or less of a salt.

19. The method of claim 1, wherein the salt comprises alkali metal ions.

20. The method of claim 1, wherein the salt comprises an anion selected from the group consisting of phosphate, sulfate, carbonate, bicarbonate, and hydroxide.

21. The method of claim 1, wherein the salt comprises ions of potassium, cesium, sodium, rubidium, or a combination thereof.

22. The method of claim 1, wherein the salt comprises magnesium carbonate, calcium carbonate, cesium carbonate, or potassium carbonate.

23. The method of claim 1, wherein the carbon oxide is carbon dioxide, carbon monoxide, or a combination thereof.

24. The method of claim 1, wherein the carbon-containing reduction product is carbon monoxide, a hydrocarbon, or an organic oxy gen-containing compound.

25. The method of claim 1, wherein the gas supplied at step d) further comprises water vapor.

26. The method of claim 1, wherein the carbon oxide supplied at step d) is a humidified carbon oxide.

27. A method of preparing an electrochemical cell comprising: a) activating an anion exchange membrane to form an activated anion exchange membrane; b) rinsing the activated anion exchange membrane with water for between about 1 hour and about 48 hours to form a rinsed activated anion exchange membrane; and c) assembling the electrochemical cell comprising a membrane electrode assembly, wherein the membrane electrode assembly comprises: i) a cathode; ii) an anode; and iii) the rinsed activated anion exchange membrane disposed between the cathode and the anode.

28. The method of claim 27, wherein step a) comprises: soaking the anion exchange membrane in an 0.5 to 2 M solution of a first electrolyte for about 1 to 48 hours.

29. The method of claim 28, wherein the first electrolyte comprises potassium hydroxide, sodium hydroxide, or calcium hydroxide.

30. The method of claim 28, further comprising rinsing the anion exchange membrane with water and then soaking the anion exchange membrane for about 48 to 72 hours in an 0.5 to 2 M of a second electrolyte before step b).

31. The method of claim 30, wherein the second electrolyte comprises magnesium carbonate, calcium carbonate, or potassium carbonate.

32. A method of activating an electrochemical cell comprising: a) providing an electrochemical cell comprising a membrane electrode assembly, wherein the membrane electrode assembly comprises i) a cathode, ii) an anode, and iii) an anion exchange membrane disposed between the cathode and the anode and in contact with an anolyte solution, wherein the anolyte solution comprises about 100 mM or less of a salt and wherein the anolyte solution is supplied from an anolyte reservoir; b) applying a first current density to the electrochemical cell; c) measuring conductivity of the anolyte solution in the electrochemical cell; d) detecting a conductivity of the anolyte solution greater than a desired setpoint conductivity, such conductivity representing an elevated conductivity; and e) performing an adjustment operation, the adjustment operation comprising one or more of: (i) replacing the anolyte solution with water, (ii) lowering a concentration of the salt in the anolyte solution within the anolyte reservoir, and (iii) reducing the first current density to a second current density, until the conductivity of the anolyte solution is reduced to less than or equal to the desired setpoint conductivity.

33. The method of claim 32, wherein step c) of measuring the conductivity of the anolyte solution is performed in the anolyte reservoir.

34. The method of claim 32, wherein the first current density is greater than about 10 mA / cm2and wherein the second current density is about 5 mA / cm2or less.

35. The method of claim 32, wherein reducing the first current density to the second current density is accomplished all at once.

36. The method of claim 32, wherein reducing the first current density to the second current density is accomplished in multiple increments.

37. The method of claim 32, wherein reducing the first current density to the second current density is accomplished in a continuous ramp.

38. The method of claim 32, wherein the adjustment operation is lowering a concentration of the salt in the anolyte solution within the anolyte reservoir to a salt concentration that is greater than zero and less than 100 mM.

39. The method of any one of claims 33-38, wherein the elevated conductivity is at least about 10% greater in magnitude than the desired setpoint conductivity.

40. The method of claim 32, wherein the salt comprises alkali metal ions.

41. The method of claim 32, wherein the salt comprises an anion selected from the group consisting of phosphate, sulfate, carbonate, bicarbonate, and hydroxide.

42. The method of claim 32, wherein the salt comprises ions of potassium, cesium, rubidium, or a combination thereof.

43. The method of claim 32, wherein the salt comprises magnesium carbonate, calcium carbonate or potassium carbonate.

44. The method of claim 32, wherein the desired setpoint conductivity is 400 pS / cm.

45. The method of claim 32, wherein the anion exchange membrane is an activated anion exchange membrane, and wherein the anion exchange membrane is activated by soaking the anion exchange membrane in an 0.5 to 2 M solution of a first electrolyte for about 1 to 48 hours; rinsing the anion exchange membrane with water; soaking the anion exchange membrane for about 1 to 72 hours in an 0.5 to 2 M of a second electrolyte; and then rinsing the anion exchange membrane with water for between about 1 hour and about 48 hours.

46. A COXreduction reactor comprising: an electrochemical cell, the electrochemical cell comprises a membrane electrode assembly comprising a) a cathode; b) an anode; andc) an anion exchange membrane disposed between the cathode and the anode; an anolyte reservoir for an anolyte salt solution; an anolyte salt solution recirculation loop; anolyte salt solution evacuation lines; a water reservoir; a water delivery line; a power supply for supplying a current density; a pump configured to circulate an anolyte salt solution; and an electrical conductivity measurement device configured to measure conductivity of the anolyte salt solution.

47. The COXreduction reactor of claim 46, configured to perform an anolyte salt solution restoration operation.

48. The COXreduction reactor of claim 47, wherein the anolyte salt solution restoration operation comprises one or more operations selected from (i) replacing the anolyte salt solution with water, (ii) lowering a salt concentration of the anolyte salt solution within the anolyte reservoir, and (iii) reducing the current density.

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