Electrode assembly and electrolyser

Abstract

The present invention relates to electrode assemblies and electrolyzers using one or more of said assemblies. In particular, the present invention provides an electrode assembly for the production of hydrogen, said assembly comprising: i) an anode structure comprising an anode located within an electrolysis chamber, ii) a cathode structure comprising a cathode located within an electrolysis chamber containing a solution of an alkali metal hydroxide, characterized in that said cathode comprises: a) an electrically conductive metal substrate, and b) an electrocatalytic layer on said substrate, and comprising a. at least one metal selected from the group consisting of platinum group metals, rhenium, nickel, cobalt and molybdenum, and b. at least 50 vol-% of an electrically conductive carrier material, wherein said electrically conductive carrier material is formed of particles having an average particle size of less than 5 micrometers (5 µm) and which are not metal particles.

Description

[0001] The present invention relates to electrode assemblies and electrolyzers using one or more of the said assemblies, particularly for the electrolysis of alkali metal hydroxides.

[0002] Electrochemical methods are carried out in two general types of batteries, which employ an anode (positive electrode), a cathode (negative electrode), and a suitable electrolyte. An oxidation reaction occurs at the anode, releasing electrons. These electrons travel to the cathode, where a reduction process takes place. The reactions between the electrodes and the electrolyte depend on the battery's chemistry. Sometimes electrode materials are consumed and transformed from one form to another. Or, for example, when used for the electrolysis of alkali metal hydroxides, the electrodes act as mediators of charge entering the electrolyte from the rectifier without affecting its composition. This process is accomplished by ions migrating from one electrode through the electrolyte to the other.

[0003] A reaction occurs spontaneously in a galvanic cell (also known as a voltaic cell) to produce electrical energy. This is because the net conversion of reactants to products is accompanied by a negative Gibbs free energy change. The amount of power produced depends on the reaction rate (current) and the potential difference (voltage) across the two electrodes in the cell. Examples of such devices include fuel cells and batteries.

[0004] In an electrolytic cell, the Gibbs free energy change throughout the process is positive, and the reaction does not occur spontaneously. Therefore, it must be driven and maintained by a DC power supply. Examples of such devices include alkaline electrolyzers and membrane chlor-alkali electrolyzers.

[0005] By convention, the voltage (V) and current (I) delivered by a galvanic cell are positive, and the power generated is equal to V*I. In an electrolytic cell, the current flows in the opposite direction, and the voltage is negative.

[0006] A further classification of electrochemical devices is those that can switch between galvanic cell and electrolytic operations. An important example is the rechargeable cell (battery). In this device, during power generation mode (called discharging), the potential difference across the cell is positive, and current flows forward. During power dissipation mode (called recharging), the potential difference reverses, and current flows backward. Therefore, the electrodes in the device must operate under both forward and reverse current configurations without damage to allow for its use in many charge-discharge cycles. This process is accomplished through a reversible chemical reaction within the package.

[0007] Electrolyzers are primarily designed to operate with current flowing in the forward direction. In the open circuit (no current flowing), the electrodes reach equilibrium potentials (typical of a reversible reaction) and equilibrium cell voltages. When the electrolyzer is energized and current flows in the forward direction, forming the desired product, a significant voltage increase is observed (conventionally in the negative polarity). The anode electrode potential increases while the cathode potential decreases; this effect is called polarization. The magnitude of polarization is commonly referred to as overpotential or overvoltage. Electrodes that can only maintain current flow under large overpotentials result in a significant increase in energy consumption per unit of product formed.

[0008] During stable operation of the electrolyzer, there is a continuous consumption of reactants to form products, effectively converting the feed chemicals and consumed electrical energy into stored chemical potential energy. Product chemicals are typically removed (stored chemical potential energy). However, when the electrolyzer power is turned off, any products remaining at the electrode sites can spontaneously react, and the cell then operates in a galvanic cell sense, thus releasing the stored energy. When this occurs, the anode electrode potential will drop below the reversible potential, while the cathode potential will rise above it, and current will flow in reverse through the cell, provided there is an electrical connection between the anode and cathode. If the amount of reverse polarization is significant, this can damage the electrodes; if frequent reverse currents are encountered, such effects accumulate.

[0009] In industry, the presentation of electrolyzer performance data is usually the opposite of this convention, and the battery voltage data presented as "negative polarity" in this specification is equivalent to this alternative convention.

[0010] This invention is highly advantageous in bipolar electrolyzers, which can have a large number of electrolytic chambers in series, resulting in a large reverse current upon shutdown and the potential for rapid damage to unsuitable cathode coatings. However, it is also advantageous in unipolar electrolysis, where the process of short-circuiting the electrolyzer to stop it from operating before maintenance generates a significant reverse current.

[0011] Many studies have focused on reducing overpotentials in such systems. This includes the use of electrocatalyst coatings applied to the electrodes. Examples of electrolyzers (particularly bipolar electrolyzers) are described, for example, in GB 1581348 or US 6761808. A bipolar electrolyzer for electrolyzing aqueous solutions of alkali metal chlorides and alkali metal hydroxides to produce chlorine and hydrogen can comprise an electrode module containing an anode and a cathode, the anode suitably being in the form of a plate or mesh of a film-forming metal (typically titanium), and the cathode suitably being in the form of a perforated plate or mesh of a metal (typically nickel or low-carbon steel). One or both electrodes may have an electrocatalyst coating. The anode and cathode are separated by a separator (typically a membrane) to form the module.

[0012] In commercial modular electrolyzers, multiple such modules are placed sequentially, with the anode of one bipolar module adjacent to and electrically connected to the cathode of an adjacent bipolar module. Another type of bipolar electrolyzer is the so-called "filter press electrolyzer," as described, for example, in GB 1595183. In these electrolyzers, bipolar electrode units are formed, each containing an anode and a cathode structure electrically connected to each other. These bipolar electrode units are then connected to adjacent bipolar electrode units via partitions and sealing devices between flanges on adjacent units, and these units are pressed together to form a filter press electrolyzer. Bipolar electrolyzers can also be used to produce oxygen and hydrogen. In this case, both the anode and cathode chambers can contain a solution of alkali metal hydroxides.

[0013] Examples of coatings applied to an anode used for chlorine production in such systems include US 2011 / 024289, US 2014 / 224666, and US 2014 / 224667.

[0014] However, the present invention relates to coatings applied to cathodes, and particularly to cathodes for the electrolysis of alkali metal hydroxides. An example of a coating applied to a cathode is found in EP 0129374B 1, which describes the application of a mixture of platinum group metals and platinum group metal oxides to a metal substrate, and is said to provide an improvement in overpotential. Another example of a coating applied to a cathode is found in WO 01 / 28714. In this document, metal particles are coated with an electrocatalytic metal or a mixture of an electrocatalytic metal continuous phase and particulate material to form a catalytic powder. The particulate material can be selected from a range of metal oxide materials. When the catalytic powder is applied as a coating to the cathode, it is said to increase the surface area and reduce the overpotential.

[0015] An alternative is described in CN 107858701A. This document provides a porous titanium substrate formed from titanium particles with a diameter of 20-50 micrometers (20-50 μm). Vertically oriented titanium oxide nanotubes are grown from the substrate surface, and then noble metal nanoparticles are deposited on them.

[0016] Limited research has progressed to the development of electrode coatings resistant to reverse current. Examples of coatings applied for hydrogen gas evolution are given in EP2539490B1, which claims several methods for improving the reverse current tolerance of the cathode electrode. These include the use of metal nitrates (particularly ruthenium nitrite nitrate) and the incorporation of stabilizing rare earth metals (e.g., praseodymium) over chlorides, showing a reduction in the negative impact of cathode potential cycling in a manner considered by the inventors to be equivalent to the reverse current in the electrolyzer. US 5494560 discloses the production of stable cathodes with low hydrogen overvoltages by applying an electrode active layer to a substrate comprising nickel and at least one of platinum, rhodium, iridium, and palladium supported on activated carbon. However, the production of cathodes that are both resistant to reverse current and have improved overvoltages remains desirable.

[0017] We have now discovered that improved cathodes can be obtained by applying a specific coating to the cathode. The coating not only provides a low overpotential for the cathode, but it also provides a cathode with a stable overpotential over extended operating cycles. The cathode can provide a high level of reverse current tolerance. In particular, the cathode of the present invention has been found to be stable under multiple shutdown and battery short-circuit cycles. The stability of the cathode improves its performance and lifespan.

[0018] Therefore, in a first aspect, the present invention provides an electrode assembly for producing hydrogen, the assembly comprising: i) Anode structure, which includes an anode located within the electrolysis chamber, ii) A cathode structure comprising a cathode located within an electrolytic chamber containing an alkali metal hydroxide solution. The cathode is characterized by comprising: a) Conductive metal substrate, and b) An electrocatalytic layer on the substrate, and comprising a. At least one metal selected from the platinum group metals, rhenium, nickel, cobalt, and molybdenum, and b. At least 50% by volume of a conductive carrier material, wherein the conductive carrier material is formed of particles with an average particle size of less than 5 micrometers (5µm) and which are not metallic particles.

[0019] The cathode comprises a conductive metal substrate. This substrate can be any conventional metal substrate known in the art. The conductive metal substrate can be a rigid structure, i.e., formed of one or more perforated metal plates, optionally louvered (slatted). Alternatively, the conductive metal substrate can be in the form of a metal fabric or wire mesh or net, such as an expanded mesh or woven mesh. Typical materials used for the substrate include stainless steel, low-carbon steel, nickel, or copper. Nickel is preferred.

[0020] In this invention, an electrocatalytic layer is present on the substrate.

[0021] The electrocatalytic layer comprises at least one metal selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum. Preferably, the electrocatalytic layer comprises at least one platinum group metal. Platinum, palladium, and ruthenium, either alone or in mixture, are preferred. Particularly preferred electrocatalytic layers comprise ruthenium alone or mixtures of ruthenium with platinum and / or palladium.

[0022] It should be noted that, at least after the deposition described below, the "at least one metal" in the electrocatalytic layer can be in the form of a "metal" (i.e., as an elemental metal) or in the form of a metal compound (e.g., an oxide). For example, ruthenium typically forms an oxide upon heating in air after deposition.

[0023] The amount of at least one metal applied to the electrode depends on the metals within the coating and their respective proportions, and this amount is selected to provide an optimal balance between long operating life and tolerance to reverse current, reduced cell voltage, and cost. Typically, the electrocatalytic layer contains at least one metal selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum, in an amount of 0.5–50 g / m³. 2 This represents the weight of the conductive metal substrate per unit surface area (based on the geometric surface area before coating). Preferred values ​​vary within this range.

[0024] For example, in coatings containing platinum group metals, preferably, the electrocatalytic layer comprises at least one metal selected from platinum group metals in an amount of 0.5-20 g / m³. 2 , which represents the weight of platinum group metals per unit surface area of ​​the conductive metal substrate (before coating).

[0025] More specifically, for platinum-containing coatings, the platinum is preferably present at a concentration of 0.5-5 g Pt / m 2 The level of ruthenium is present in this layer. When using platinum, such a level provides acceptable lifespan and cost. Layers containing ruthenium, including those containing small amounts of other metals (molar ratio), preferably contain 2-15 g Ru / m 2 Ruthenium can be used alone or in combination with other metals, particularly other platinum group metals. For example, when ruthenium and platinum are used in a molar ratio of 9:1 Ru:Pt, the ruthenium coating weight is 10 g Ru / m 2 At that time, this translates to a platinum coating weight of 2.15 g Pt / m 2 The palladium-containing layer preferably contains 0.5-5 g Pd / m 2 Palladium can be used alone or in combination with other metals, particularly other platinum group metals. For example, when palladium and ruthenium are used in a 9:1 Ru:Pd ratio, and the ruthenium coating weight is 10 g Ru / m³,... 2 At that time, this translates to a palladium coating weight of 1.2 g Pd / m 2 .

[0026] The electrocatalytic layer further comprises at least 50% by volume of a conductive carrier material, which is formed of particles with an average particle size of less than 5 micrometers (5 μm) and are not metal particles.

[0027] The carrier material can be a metal oxide or other metal compound, or it can be nonmetallic, such as carbon. Some preferred materials are provided below. Generally, the carrier material should be chemically and electrochemically stable under the conditions of the electrolyzer and under reverse current flow. In particular, during use in the electrolyzer, the carrier material should not undergo any chemically or electrochemically induced changes that significantly affect the performance of the coating containing the carrier material, i.e., cause its voltage performance to deteriorate over a short period relative to the normal lifespan of the electrode (which is typically several years). Chemical and electrochemical stability can be determined by analyzing voltage performance in suitable tests. An example of a suitable test is described in the embodiment of EP2539490B1. In this invention, chemical and electrochemical stability can preferably be determined by the tests described in Example 4 below. In “normal” operation, i.e., electrolysis with a forward current, the tests described in detail in Example 4 below are performed for most of the time. However, once daily, before the electrolyzer returns to normal operation, the anode and cathode are short-circuited to induce a reverse current. This cycle is repeated while monitoring the battery voltage, which has stabilized during normal operation. This allows for multiple shutdowns within a relatively short period to simulate the cumulative effects typically accumulated over several years of operation in a factory. In this invention, the carrier material is considered chemically and electrochemically stable if the voltage (negative) increase after 30 cycles in this test is less than 100 mV of the initial voltage. Preferably, the voltage (negative) increase after 30 cycles is less than 50 mV of the initial voltage.

[0028] A particular feature of this invention is that the conductive carrier material is formed from particles with an average particle size of less than 5 micrometers (5 μm). Preferably, the conductive carrier material is formed from particles with an average particle size of less than 1 micrometer (1 µm), and even more preferably less than 0.5 micrometers (500 nanometers), for example, 10-250 nanometers. A preferred average particle size is 20-100 nanometers.

[0029] As used herein, when the particles to be deposited are spherical or near-spherical, the size of each individual particle is its average diameter in all directions, i.e., the diameter of a sphere with an equivalent volume. However, it is not necessary to determine the size of each particle individually, and the average particle size used can be determined by any conventional technique, such as dynamic light scattering, electrophoretic light scattering, laser diffraction, electrozone sensing, and sedimentation.

[0030] When the particles to be deposited are elongated, such as nanotubes, the particle size used in this paper should be considered as the size in the longest dimension, and the average particle size can be determined accordingly based on that dimension.

[0031] For example, in US 5494560, the carbon particles used are in the range of 10-100 micrometers (10-100 μm). Example 1 in US 5494560 shows that this results in a hydrogen overpotential of 70-80 mV. However, in this invention, overpotentials of 60 mV and lower are typically obtained. This is illustrated in the examples below.

[0032] In particular, and not wanting to be bound by theory, it is assumed that during application to the substrate, the deposited particles form a porous layer with channels between the particles, which provides both the desired porosity and surface area in the electrocatalytic layer. Porosity is in the form of a three-dimensional network of channels between the deposited particles.

[0033] More specifically, the average diameter (D) of the channels between particles is preferred. 50 The pore volume is between 5 and 500 nm. In the most preferred embodiment, at least 50% of the total pore volume is due to pores with diameters between 5 and 500 nm. In this embodiment, the pore volume distribution shall be measured using the mercury intrusion porosimetry method according to ASTM D4284-12(2017) E1 (“Standard Test Method for Determining Pore Volume Distribution of Catalysts and Catalyst Carriers by Mercury Intrusion Porosimetry”).

[0034] Conductive carrier materials, especially when said materials comprise conductive carbon materials as discussed further below, typically have a surface area of ​​at least 50 m². 2 / g, for example, at least 200 m 2 / g. Surface area can be up to 2000 m². 2 / g, preferably up to 1500 m 2 / g, but the optimal value is 200-1000 m 2 / g (Surface area should be measured using ASTM D3663-03(2015) “Standard Test Method for Surface Area of ​​Catalysts and Catalyst Carriers”).

[0035] The thickness of the electrocatalyst layer is typically 0.5-100 micrometers (0.5-100 μm), preferably 0.5-20 micrometers (0.5-20 µm). Preferably, the layer is uniformly coated onto the substrate, meaning that the thickness at any point is within 50% of the average thickness. The coating covers the front, back, and inner surfaces of the electrode. Coating is preferably achieved by spraying (optionally as a multilayer coating), as discussed further below.

[0036] Of particular importance in this invention is that the carrier material particles are conductive, but not metallic. Specifically, it has been found that conductivity allows for the dissipation of stored charge under reverse current flow. However, while metallic particles are conductive, particles of some commonly used metals (e.g., nickel and ruthenium) have been found to be not electrochemically stable. Such metals are lost from the coating through dissolution during the dissipation of stored charge. When the process is restarted after shutdown, the coating efficiency decreases when such metallic particles are used as the carrier material. For example, it has been found that using transition metal carriers in particulate form (e.g., Raney nickel) provides limited voltage stability because they eventually deactivate when hydrides are incorporated into the electrode surface. Furthermore, they are prone to pyrolysis upon contact with air during maintenance.

[0037] Unwilling to be bound by theory, during battery tripping, a damage mechanism can occur that could lead to further deactivation of the cathode used in chlor-alkali production, due to the migration of hypochlorite ions driven by reverse current into the cathode electrolyte solution. The reduction of hypochlorite ions at the cathode then leads to the oxidation of the metal, as described in the following equation: OCl - + H2O + 2e → Cl - + 2OH - (Cathode reaction) M → M 2+ + 2e (anodic reaction) Preferably, the resistivity of the conductive carrier material is less than 10. -3 Ωm, for example 10 -3 Up to 10 -4 Ωm.

[0038] In one embodiment, the conductive carrier material may be a conductive metal oxide. Examples include binary metal oxides such as titanium oxide (TiOx), tungsten oxide (WOx), molybdenum oxide (MoOx), cerium oxide (CeOx), lanthanum oxide (La2O3), manganese oxide (MnOx), indium oxide (In2O3), hafnium oxide (HfO2), tantalum oxide (Ta2O5), and multi-component metal oxides such as perovskite (ABO3) supergroup and pyrochlore (A2B2O6) oxide group. Other examples include metal carbides, such as tungsten carbide.

[0039] It can be noted that some materials that can be used as conductive support materials can be oxides of metals that are the "at least one metal" component that can be used as an electrocatalytic layer. However, the two components are distinct and must be present. Specifically, the conductive support material must be present in an amount of at least 50% by volume of the electrocatalytic layer and must be formed from particles with a defined maximum size. The "at least one metal" must be loaded onto the conductive support material. Therefore, even when formed from chemically related materials, the two components are distinctly different.

[0040] Preferably, the conductive carrier material comprises a conductive carbon material. Typical carbons include carbon black, graphite, acetylene black, graphene, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs). Specific examples of suitable carbons include BlackPearls 2000 sold by Cabot Corporation under the trade name Vulcan XC-72R, or available from Cabot Corporation in the United States, or Ketjen black EC600JD or EC300JD available from Lion Specialty Chemicals Co. Ltd in Japan. The carbon material can be used alone or in combination with other carbons as a conductive carrier material, or one or more carbons can be mixed with one or more metal oxides (e.g., praseodymium oxide, neodymium oxide, or one or more conductive metal oxides selected from the conductive metal oxides listed above).

[0041] When the conductive carrier material is carbon black, it should be recognized that the combustion process used to produce carbon black generates so-called "primary particles" of carbon, whose average size can vary within a certain range depending on the raw materials and combustion conditions, but is typically less than 500 nm. Due to their small size and high surface area, these primary particles will aggregate under the influence of van der Waals forces to form larger aggregates with sizes ranging from 0.1 to 50 micrometers (0.1 to 50 µm). The aggregate size can preferably be 0.1 to 20 micrometers (0.1 to 20 µm). However, as used herein, references to conductive carrier materials formed from particles with an average particle size smaller than a specific size (e.g., less than 5 micrometers (5 μm)) refer to the size of the primary particles in such cases, and not to any aggregates that may form.

[0042] In this invention, the electrocatalytic layer comprises at least 50% by volume of conductive support material, that is, at least 50% of the majority volume of the layer is composed of support material. Preferably, the electrocatalytic layer comprises at least 55% by volume, more preferably at least 60% by volume, more preferably at least 80% by volume, and most preferably at least 90% by volume of conductive support material (i.e., preferably at least 55% by volume, more preferably at least 60% by volume, more preferably at least 80% by volume, and most preferably at least 90% by volume of the electrocatalytic layer is conductive support material).

[0043] In addition to the conductive support material, the electrocatalytic layer also contains at least one metal selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum (these metals are referred to as "electrocatalytic metals" below). Typically, these are present in amounts from 0.1 vol% to up to the remainder of the layer, and preferably from 0.2 vol% to up to the remainder of the layer. Therefore, the electrocatalytic layer contains less than 50 vol%, preferably less than 45 vol%, more preferably less than 40 vol%, more preferably less than 20 vol%, and most preferably less than 10 vol% of the electrocatalytic metal. (That is, less than 50 vol%, preferably less than 45 vol%, more preferably less than 40 vol%, more preferably less than 20 vol%, and most preferably less than 10 vol% of the electrocatalytic layer is an electrocatalytic metal).

[0044] Most preferably, the electrocatalytic layer comprises 0.2-10% by volume of a layer of at least one metal selected from platinum group metals, rhenium, nickel, cobalt and molybdenum, and 90-99.8% by volume of a layer of conductive carrier material.

[0045] The amount of at least one electrocatalytic metal and conductive support material, expressed in moles, depends on the relative density of each material. When the conductive support material is conductive carbon, the electrocatalytic layer typically comprises 40-80 mol% of at least one electrocatalytic metal and 60-20 mol% of the conductive support material.

[0046] In WO 01 / 28714, the coating comprises only an electrocatalytic metal, or the electrocatalytic metal is a continuous phase having metal oxide particles embedded therein. In this invention, the support particles are selected to be conductive, and the support particles are also the main component of the coating, on which at least one electrocatalytic metal is loaded. This provides the advantages of a significantly higher active surface area per gram of at least one electrocatalytic metal, resulting in a lower cathode overpotential, increased impurity tolerance, and providing the opportunity to reduce the amount of at least one electrocatalytic metal required to deliver equivalent catalytic activity, thus reducing costs.

[0047] In this invention, at least one electrocatalytic metal can be loaded onto a conductive support material in the electrocatalytic layer by any suitable method.

[0048] Preferably, a material is provided prior to coating, wherein at least one electrocatalytic metal is loaded onto a conductive support material. For example, such a material may be pre-formed or manufactured and purchased prior to coating. However, a physical mixture of one or more electrocatalytic metals and a conductive support material may also be supplied and applied to a substrate, so that at least one electrocatalytic metal will only be loaded during application.

[0049] Electrocatalytic metals can exist as a continuous layer on the surface of a conductive support, or they can be dispersed as particles on the conductive support.

[0050] Typically (including whether the electrocatalytic metal is loaded onto a conductive support material prior to deposition / coating, or whether it is supplied separately during deposition / coating), the electrocatalytic metal exists in particulate form, and the average particle size of the deposited electrocatalytic metal particles is typically significantly smaller than the average particle size of the conductive support material used in the electrocatalytic layer. Typically, the average particle size of the deposited electrocatalytic metal particles is less than 20% of the average particle size of the conductive support material used in the electrocatalytic layer.

[0051] In this invention, the conductive carrier material is formed from particles with an average particle size of less than 5 micrometers (5 μm). Therefore, as a maximum, the average particle size of the deposited electrocatalytic metal particles should be less than 1 micrometer (1 μm). Typically, the average particle size will be significantly smaller than this value. Preferably, the average particle size of the deposited electrocatalytic metal particles is less than 0.2 micrometers (200 nanometers), and even more preferably less than 0.1 micrometers (100 nanometers), for example, 2-50 nanometers. A preferred average particle size is 2-20 nanometers.

[0052] More generally, the electrocatalytic layer on a conductive metal substrate (and comprising at least one metal supported on a conductive carrier material) is preferably formed by depositing the following on said substrate: i. Particles of conductive carrier materials with an average particle size of less than 5 micrometers (5 μm), and ii. Particles of at least one metal selected from platinum group metals, rhenium, nickel, cobalt and molybdenum, having an average particle size less than 20% of the average particle size of the conductive carrier material.

[0053] It should be noted that, as already described, at least one metal particle may and preferably has been loaded onto particles of a conductive carrier material before being deposited onto the substrate.

[0054] More generally, an electrocatalytic layer can be applied to a conductive metal substrate using any suitable technique, including those described in this art for other (e.g., anode) applications. (Including the references mentioned above describing anode and cathode coatings.) A “paint” is typically formed and used for application. The exact method of forming the “paint” depends on the form of the material used and the chosen method of applying it to the electrode, but such techniques are conventional and well known to those skilled in the art. For example, a paint can be formed by dissolving one or more metal precursor compounds in a suitable solvent, adding an insoluble carrier material, and then forming a dispersion. If the metal is already loaded on a carrier, a dispersion of the material can be formed without the separate dissolution of the metal compound. As known to those skilled in the art, other additives (e.g., rheology modifiers) can be added to maintain the dispersion or improve its applied viscosity. Additionally, in cases where the metal is pre-loaded on carbon, a binder can be added to aid adhesion within the layer and to the electrode substrate.

[0055] The coating can be applied to the substrate using any suitable application method. Examples include dip coating and brush coating. A preferred example is spray coating, especially on an industrial scale. The electrocatalytic layer is preferably applied to the substrate by applying multiple coatings. Using multiple coatings is advantageous for producing a more uniform, denser, crack-free layer and the most efficient coverage of the substrate (because it is statistically impossible to miss any area with more coating). Typically, a total of 2-20 coatings can be applied.

[0056] However, the applied coating is typically dried after each coating and before the next coating is applied. The drying temperature depends on the coating technique and, in particular, the solvent or solution used, but is generally carried out at 100-200°C for 1-10 minutes. Depending on the coating technique, it may also be advantageous to heat the coating at a higher temperature between coatings. In some embodiments, this may be carried out at a temperature in the range of 300-500°C for 10-30 minutes, although this also depends on the coating technique, and temperatures and times outside these ranges may also be used. Some specific examples are described in the embodiments herein. More generally, methods for coating electrodes are known in the art, and the temperatures and conditions to be used can be determined by those skilled in the art based on the coating technique.

[0057] The conductive metal substrate can be physically or chemically treated to improve the adhesion of the electrocatalytic layer. For example, the substrate can be roughened by grinding (or sandblasting), chemical etching, or similar treatments before coating.

[0058] In some embodiments of the invention, a chemical layer may be provided between the conductive metal substrate and the electrocatalytic layer. For example, an adhesive layer may be applied to the conductive metal substrate prior to the electrocatalytic layer. As used herein, "adhesive layer" refers to a chemical layer that improves the adhesion of the electrocatalytic layer to the conductive metal substrate.

[0059] In other embodiments, instead of adding a binder before the electrocatalytic layer, the electrocatalytic layer can be applied. This can be achieved by adding a binder (e.g., PTFE or an ionomer) to a coating dispersion containing the following substances: a. At least one metal selected from the platinum group metals, rhenium, nickel, cobalt, and molybdenum, and b. At least 50% by volume of conductive carrier material, And apply the mixture as a coating.

[0060] Typically, the electrocatalytic layer containing the binder is heat-treated at a temperature sufficient to sinter the binder, which provides improved adhesion of the electrocatalytic layer.

[0061] In some embodiments of the present invention, two or more electrocatalytic layers may be sequentially deposited on a substrate, i.e., each layer comprises: a. At least one metal selected from the platinum group metals, rhenium, nickel, cobalt, and molybdenum, and b. At least 50% by volume of conductive carrier material as defined herein, but wherein the deposited layers differ in composition, for example, in one or more metals or carrier materials used.

[0062] The first layer can be used to improve the adhesion of subsequent layers or layers. Obviously, such layers can also be considered as “adhesive layers” as defined above. However, for the purposes of this application, when they also contain both a metal and a carrier material as defined herein, we refer to them as “primer layers”.

[0063] When a primer layer is used, each layer is typically formed by applying several coatings of the desired composition (e.g., 2-10 coatings for each composition, and independently). Preferably, in the case of using a primer layer, there are two electrocatalytic layers: the primer layer and a second or "top" layer deposited thereon.

[0064] Apart from the electrocatalytic layer on the cathode, the electrode assembly for hydrogen production according to the present invention can be of a conventional design. An example of a preferred design is described in US 6761808 B1, which has already been mentioned.

[0065] In use, the anode chamber and cathode chamber will each contain the solution to be electrolyzed. (The term "chamber" refers to a portion of the anode or cathode structure containing the anode or cathode and the solution to be electrolyzed.) In use, the components of the present invention can be used in any method in which the alkali metal hydroxide is present in the cathode chamber of the electrode assembly.

[0066] In one embodiment, the electrode assembly can be used to produce hydrogen and halogens. In this case, the anode chamber contains a solution of an alkali metal halide, which is electrolyzed to produce halogens. Preferably, the alkali metal halide is a chloride, and more preferably sodium chloride. The alkali metal hydroxide is preferably sodium hydroxide. Electrochemical cells for producing halogens and hydrogen are well known, for example, as described in US 6761808 B1, which has already been mentioned.

[0067] In another embodiment, the electrode assembly can be used to produce hydrogen and oxygen. In this case, the anode chamber also contains a solution of an alkali metal hydroxide, which is electrolyzed to produce oxygen. Preferably, the alkali metal hydroxide in both chambers is potassium hydroxide or sodium hydroxide. Electrochemical cells for producing oxygen and hydrogen are also known, and are commonly referred to as alkaline water electrolysis. For example, see Advances in Hydrogen Generation Technologies - Chapter 1 'Hydrogen Generation by Water Electrolysis' by Youssef Naimi and Amal Antar - Chapter 4. (Published online by IntechOpen).

[0068] The electrode assembly of the present invention includes an anode structure and a cathode structure, the anode structure including an anode located in an electrolysis chamber, and the cathode structure including a cathode located in an electrolysis chamber.

[0069] In practice, the electrode assemblies will be used in modular or filter press electrolyzers that contain multiple connected electrode assemblies.

[0070] More specifically, as used herein, the term “electrode assembly” encompasses both monopolar and bipolar assemblies, the latter being bipolar electrode units or bipolar electrode modules, depending on how the anode and cathode structures are connected.

[0071] Specifically, a "bipolar electrode unit" is an electrode assembly comprising an anode structure and a cathode structure electrically connected to each other. Bipolar electrode units can be connected to adjacent bipolar electrode units via partitions and sealing devices between flanges on adjacent units to form a filter press electrolyzer.

[0072] An "electrode module" is an electrode assembly comprising an anode and a cathode structure, separated by a partition between corresponding flanges. The electrode module is equipped with sealing devices to achieve liquid-tight and gas-tight seals between the partitions and the corresponding flanges. Electrode modules can be electrically connected to adjacent electrode modules to form a modular electrolyzer.

[0073] Therefore, in a second aspect, a modular or filter press electrolyzer is provided, which includes multiple electrode assemblies as described above. Typically, a modular or filter press electrolyzer contains 5-300 electrode assemblies.

[0074] Further details regarding bipolar electrode units, electrode modules, modularization, and filter press electrolyzers can be found in the art, for example, WO2016169813A1.

[0075] In a third aspect, an electrolysis method is provided, the method comprising electrolysis in an electrode assembly or in a modular or filter press electrolyzer as described above to produce hydrogen.

[0076] Further details regarding the operation of such systems can be found again in the art, for example, WO2016169813A1. Typically, hydrogen evolution electrolyzers (e.g., alkaline water electrolyzers) can operate at pressures between 50 and 15000 kPa (0.5-150 bar) absolute pressure, preferably between 50 and 500 kPa (0.5-50 bar) absolute pressure. When the electrolyzer is a modular or filter press chlor-alkali electrolyzer, these typically operate at pressures between 50 and 600 kPa (0.5-6 bar) absolute pressure, preferably between 50 and 180 kPa (500-1800 millibar) absolute pressure.

[0077] The liquid to be electrolyzed is fed into the inlet pipe in each electrode structure. For example, the inlet pipe allows alkali metal hydroxides to be loaded into the cathode structure and the desired solution to be loaded into the anode structure. Products, such as chlorine and depleted brine solution from the anode structure and hydrogen and alkali metal hydroxides from the cathode structure, are recovered from the corresponding manifolds.

[0078] In the chlor-alkali process, high current densities (e.g., >6 kA / m) can be achieved. 2 Electrolysis is performed under the following conditions.

[0079] As described above, the coating of the present invention has been found to provide a low cathode overpotential, a stable overpotential of the cathode over an extended operating period, and a high level of reverse current tolerance.

[0080] Therefore, in a fourth aspect, the present invention provides the use of an electrocatalytic layer on an electrode, said electrode comprising a) Conductive metal substrate, and b) An electrocatalytic layer on a substrate, and comprising a. At least one metal selected from the platinum group metals, rhenium, nickel, cobalt, and molybdenum, and b. At least 50% by volume of a conductive carrier material, wherein the conductive carrier material is formed of particles with an average particle size of less than 5 micrometers (5 µm) and is not a metallic particle. To provide at least one of the following: i) The reduced overpotential of the electrode. ii) Overpotential of the electrode stabilized during extended operating cycles, and iii) Improved reverse current tolerance of the electrodes.

[0081] In this fourth aspect, the use of the electrocatalytic layer preferably provides at least two of the following, and more preferably all three of the following: i) The reduced overpotential of the electrode. ii) Overpotential of the electrode stabilized during extended operating cycles, and iii) Improved reverse current tolerance of the electrodes.

[0082] In particular, the preferred use of an electrocatalytic layer provides a reduced overpotential of the electrode, which is stable over extended operating cycles, and most preferably, also provides improved reverse current tolerance of the electrode.

[0083] Preferably, the electrode is the cathode in a method for producing hydrogen from the cathode. Most preferably, the method is a method for producing hydrogen from an alkali metal hydroxide at the cathode and (1) producing halogen from an alkali metal halide or (2) producing oxygen from an alkali metal hydroxide at the anode.

[0084] Finally, in a fifth aspect, the present invention provides a method comprising: i) Production electrode, the electrode comprising a) Conductive metal substrate, and b) An electrocatalytic layer on a substrate, and comprising a. At least one metal selected from the platinum group metals, rhenium, nickel, cobalt, and molybdenum, and b. At least 50% by volume of a conductive carrier material, wherein the conductive carrier material is formed of particles with an average particle size of less than 5 micrometers (5 µm) and is not a metallic particle. and ii) Supply the electrode as a cathode for a method of electrolyzing alkali metal hydroxides to produce hydrogen.

[0085] Electrodes can be produced by any known method, including those discussed above.

[0086] As used herein, “supply” can refer to the sale of an electrode in which the electrode is used as a cathode. This can include the export of the electrode from its country of manufacture.

[0087] A preferred method for producing hydrogen by electrolyzing alkali metal hydroxides is a method for producing hydrogen at the cathode and (1) producing halogens from alkali metal halides or (2) producing oxygen from alkali metal hydroxides at the anode. Such methods have been described.

[0088] The present invention will be described with reference to the following embodiments. Example

[0089] For clarity, the examples provided below encompass a series of coating formulations applied to different nickel metal electrode structures, the selection of which is determined by the test cells constructed therein for evaluation. Typically, each respective coating formulation is applied to each respective nickel metal electrode type to an equal coating level. It will also be apparent to those skilled in the art of applying electrode coatings that those produced by hand (e.g., brushing) and those produced by spraying give equivalent performance, and the examples provided below reflect this.

[0090] To further clarify, electrochemical testing is performed on a series of different electrolyte cell designs utilizing nickel metal electrodes with different coatings. This is common practice for determining different aspects of the electrode coating performance. Test data are compared with contrasting examples of coatings applied to the same nickel metal electrode, tested under identical operating conditions in the same cell configuration. The different test electrode designs are described below: (a) In the standard test, the area applied was 1.65 cm². 2 Furthermore, single-electrode potential (SEP) tests were performed on coating samples on a solid disc with a thickness of 1 mm (referred to as “Type A” electrodes) to rapidly determine the electrokinetic activity of the coating (tested several times a day; further details are provided below).

[0091] (b) Full-scale FM21 TM The electrolyzer used in the test had a height of 22 cm, a width of 95 cm, and a membrane and electrode area of ​​approximately 0.21 m². 2 The cathode is a louvered nickel plate. The vertical nickel louvers are 220 mm high × 2 mm wide × 2 mm deep, and the spacing between the louvers is 2 mm (referred to as "Type B electrode"). The anode is a louvered titanium plate with the same dimensions as the cathode. A more detailed description of the electrode and electrolyzer structure is given in US4824542.

[0092] (c) Using an expanded mesh (referred to as a "C-type" electrode) coated with a thickness of 1 mm at 2.895 m 2 (membrane area) for full-scale Bichon LoreTM Electrolyzer testing. This test is used to evaluate coating performance under real-world plant operating conditions (test durations range from several months to several years; further details are provided below).

[0093] (d) Using an expanded mesh (referred to as a "D-type" electrode) coated with a thickness of 0.15 mm at 100 cm 2 Micro-pipe-scale testing was conducted at (film area). This is a standard test used to determine the impact of established successive short-circuit shutdown events to determine the reverse current tolerance of the cathode coating (test duration is 20-30 days, further details are provided below).

[0094] 1. Single electrode potential test 1.1. Experimental setup In these embodiments, the electrochemical performance of the coatings was compared. The test used an electrochemical cell typically used by those skilled in the art to characterize the design of coatings.

[0095] The test electrode is "Type A," featuring an integrated 2mm wide stub extending from the edge to allow attachment to a titanium battery electrode fixture using titanium screws. The electrode is produced from an extended sheet that is sandblasted with molten alumina to roughen the surface for improved coating adhesion and then ultrasonically cleaned in softened water. Once coated, the electrode is cut from the sheet for use in the electrochemical cell.

[0096] The cell was operated at 85°C in a 32% NaOH atmosphere, using a platinum mesh counter electrode and a reversible hydrogen reference electrode (providing a stable reference potential of 0.000V during testing) to establish a typical 3-electrode configuration for such tests. This was achieved at 3kA / m 2 The activity of the hydrogen evolution reaction is determined by measuring the test electrode potential relative to the reference electrode at a given current density for a period of time (up to 5 hours) until stable performance is observed. The electrolytic resistance of the measured data is corrected by simultaneously measuring the cell impedance.

[0097] 1.2. preparation Comparative Example 1A: The electrode (“Type A”) is an uncoated, sandblasted nickel electrode.

[0098] Comparative Example 2A: The coating was produced by diluting a stock solution of dihydrohexachloroplatinic acid (150 g / L in 20% HCl) with glacial acetic acid to obtain a final concentration of 22 g / L. It was then sprayed in multiple layers onto pre-sandblasted electrodes, with intermediate drying at 180°C for 2 minutes between layers, followed by heat treatment in air at 480°C for 12 minutes to convert the coating into a mixture of platinum metal and platinum oxide. Coatings were repeated until the coating level reached 3-4 g Pt / m. 2 As measured by calibrated XRF. 3-4 g Pt / m 2 This is a typical load for platinum-type coatings used in industrial applications to ensure long service life. Typically, in short-term tests (such as in this embodiment), the initial overpotential is not very sensitive to precise Pt loading, provided the electrode surface is uniformly coated.

[0099] Comparative Example 3A: The platinum-containing coating was produced as in Comparative Example 2A. The coating was then modified by adding sufficient ruthenium(III) chloride crystals and stirring vigorously until completely dissolved to obtain a molar composition of 4.66:1 Pt:Ru (90% Pt, 10% Ru, by weight).

[0100] It is applied in multiple layers to the pre-sandblasted electrode (“Type A”), with intermediate drying at 180°C for 2 minutes between layers, followed by heat treatment in air at 480°C for 12 minutes to convert the coating into a mixture of platinum metal, platinum oxide, and ruthenium oxide. Coatings are repeated until the coating level reaches 3-4 g Pt / m. 2 , such as measurements taken via calibrated XRF.

[0101] Comparative Example 4A: Coatings are produced by using ultrasound to completely dissolve ruthenium(III) chloride crystals in glacial acetic acid to a concentration of 50 g Ru / L.

[0102] It was sprayed in multiple layers onto the pre-sandblasted electrode (“Type A”), with intermediate drying at 180°C for 2 minutes between layers, followed by heat treatment in air at 450°C for 12 minutes to convert the coating into ruthenium oxide. The coating was repeated until the coating level reached 10⁻¹² g Ru / m². 2 , such as measurements taken via calibrated XRF.

[0103] 10-12g Ru / m 2 This is a typical load for ruthenium electrodes used in industrial applications to ensure long service life. Typically, in short-term testing (such as in this embodiment), the initial overpotential is not very sensitive to precise Pt loads, provided the electrode surface is uniformly coated. In typical industrial applications, Ru loads are generally higher than comparable Pt loads because Ru coatings typically wear out much faster than Pt coatings.

[0104] Example 5A: This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon and ruthenium. In this embodiment, carbon and ruthenium are co-deposited.

[0105] The coating is produced by first dissolving ruthenium(III) chloride crystals in glacial acetic acid to a concentration of 33 g Ru / L using ultrasound for at least 10 minutes. A slurry is then produced by adding carbon black powder (Cabot Vulcan XC-72R) at a concentration of 7.84 g C / L and dispersing it ultrasonically for at least 30 minutes.

[0106] The resulting composition contained 2:1 C:Ru (molar ratio) (80.8% Ru, 19.20% C, by weight). It was applied in multiple layers to a pre-blasted electrode (“Type A”), with intermediate drying at 180°C for 2 minutes between layers, followed by heat treatment in air at 350°C for 12 minutes to convert the coating into a carbon-loaded amorphous ruthenium oxide coating. Coatings were repeated until the coating level reached 10⁻¹² g Ru / m². 2 , such as measurements taken via calibrated XRF.

[0107] Example 6A: This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon, platinum, and ruthenium. The coating is applied as a “double layer.”

[0108] The first layer is a C;Ru layer, which is applied to the pre-sandblasted electrode (“Type A”) by three coats using the same coating, application and drying method as given in Example 5A, except that heat treatment in air at 450°C is performed between the coatings.

[0109] This yields 3g Ru / m 2 The nominal coating weight.

[0110] The purpose of the first layer is to act as a primer layer to improve the adhesion of the second layer to the electrodes.

[0111] The second layer is applied on top of the first layer using a different coating. Specifically, 1 g of commercial carbon-supported platinum catalyst (Alfa Aesar HiSpec 4000, containing 40% by weight platinum pre-modified onto Vulcan XC-72R carbon black) is weighed into a suitable container. 20 cm³ of the catalyst is added to the catalyst at room temperature. 3Softened water was used to produce a slurry by low-shear stirring for 10 minutes using a laboratory stirrer plate and a magnetic stirrer. A polytetrafluoroethylene (PTFE) emulsion (Asahi Glass AD309E, at 59.8% PTFE) was added to the resulting slurry as a binder, and the amount was equal to 0.12 g of dry PTFE equivalent, which is equivalent to 20% by weight of carbon.

[0112] The slurry was then mixed at high speed using a laboratory mixer for 20 minutes, and the pH was lowered to approximately 2 by adding 1M H2SO4 to achieve flocculation. The resulting slurry was further stirred for 10 minutes, then gravity filtered and washed with 200 ml of softened water to remove excess acid.

[0113] The resulting filter cake was dried in air in an oven at 80°C for 2 hours to remove most of the moisture content. The resulting solid was then transferred to a suitable container and broken down to a breadcrumb consistency using a scraper. 10 ml of 2% methylcellulose gel, which acts as a rheology modifier in the final coating, was added. The gel was produced separately by dissolving methylcellulose powder (Alfa Aesar 4000 cPs) in softened water and then homogenizing it using a high-shear mixer (Silverson L5, using an emulsifier sieve) until the powder dissolved and formed a gel.

[0114] The mixture of filter cake and gel was then mixed for 10 minutes using a high-shear mixer (Silverson L5, universal pulverizer head) until a significant decrease in viscosity was observed and the coating transformed into a free-flowing Newtonian fluid suitable for coating. The resulting coating was brushed onto the electrode pre-coated with the first layer. Three coats were applied between layers, with intermediate drying at 100°C for 5 minutes to achieve 3-4 g Pt / m 2 The coating level, as measured by calibrated XRF.

[0115] After the third coating, the electrode is placed between filter papers and pressed for 10 seconds between the cold plates of a hydraulic press at a pressure of 400 psi to compact the layer.

[0116] The resulting bilayer electrode was then heat-treated in air at 350°C for 15 minutes. This caused the PTFE to melt and flow, resulting in the formation of a robust electrode coating. (Lower heat treatment temperatures resulted in suboptimal bonding of the carbon-platinum layers, and higher temperatures were avoided to prevent the decomposition of the PTFE).

[0117] Example 7A: This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon and platinum. Platinum is loaded onto carbon prior to use (“pre-modified”).

[0118] By including 1g in a high surface area carbon support (Alfa Aesar HiSpec) TM To manufacture the coating, 60% by weight of Pt catalyst powder from 9100 is added to a suitable container. 12g of dipropylene glycol monomethyl ether (Dowanol) is then added to the mixture. TM DPM) and 6g of perfluorinated sulfonic acid ionomer dispersion (10% w / w Nafion) TM DE1021 in water) to obtain a loading of 150% w / w polymer solids relative to carbon.

[0119] The purpose of ionomers is to provide a chemically and electrochemically compatible binder in the operating environment of an electrolyzer. A loading of 150% was found to produce optimal mechanical properties, with less than 100% resulting in poor adhesion, while greater than 200% leads to brittle, easily peeled electrode coatings.

[0120] The catalyst ionomer mixture is processed for 5 minutes in a high-shear mixer (Silverson L5, universal pulverizer head) to produce a stable viscoelastic coating suitable for spraying or brushing that does not settle when left to stand.

[0121] Apply multiple layers of the polymer to the pre-blasted electrode ("Type A") using a spray gun (using nitrogen propellant), perform intermediate drying between coatings, and sinter the ionomer in air at 180°C for 2 minutes. Repeat coating until the coating level reaches 3-4 g Pt / m. 2 , as measured by calibrating XRF.

[0122] Once the correct coating level is achieved, the electrodes are further heat-treated at 180°C for 30 minutes to remove any residual solvent.

[0123] Example 8A: This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon, ruthenium, and platinum. Ruthenium and platinum are loaded onto carbon prior to use (“pre-modified”). The electrode coating is produced in a manner similar to that of Example 7A, except that the catalyst powder used is high surface area carbon black (Alfa Aesar HiSpec). TM Goods on 12100) contain 50% Pt and 25% Ru.

[0124] 1.3. result Table 1 provides the average electrochemical performance of the coating for each embodiment applied to the "Type A" electrode, with data averaged several times across different electrodes / batches. The values ​​presented are equal to the coating overpotential used for the hydrogen evolution reaction.

[0125] Table 1 Comparative Example 1A provides reference performance for an uncoated nickel electrode, as measured by single electrode potential testing (SEP), at 3 kA / m. 2 The value below is -0.288V relative to RHE.

[0126] Comparative Examples 2A, 3A, and 4A show the typical performance of carbon-free industrial chlor-alkali cathode coatings, with values ​​of approximately -0.087V, -0.084V, and -0.086V for pure platinum, platinum-ruthenium (molar composition 4.66:1 Pt:Ru), and pure ruthenium, respectively.

[0127] It can be seen that, compared with the uncoated electrode (CE1), all three coatings provide an improvement in overpotential (i.e., the potential becomes less negative), and all three coatings have a comparable degree of improvement.

[0128] Example 5A provides the performance of carbon-supported ruthenium (molar composition 2:1 C:Ru) at -0.060V relative to RHE. This demonstrates an improved overpotential (improvement of 24-27 mV) for the hydrogen evolution reaction compared to comparative Examples 2A, 3A, and 4A. This translates to a similar reduction in cell voltage in industrial chlor-alkali electrolyzer battery assemblies. Example 5A shows the advantages of using carbon-supported ruthenium in enhancing electrode performance.

[0129] Example 6A provides the performance of a bilayer electrode having a first layer of carbon-loaded ruthenium and a top layer comprising a pre-modified carbon-loaded platinum and PTFE binder. This electrode structure exhibits a performance of -0.048V relative to RHE. This demonstrates an overpotential improvement of 36-39 mV compared to comparative Examples 2A, 3A, and 4A.

[0130] Example 7A provides a platinum layer containing a pre-modified carbon-supported layer and Nafion. TM The performance of the electrode for the ionomer binder. The electrode's performance is -0.060V relative to RHE. This demonstrates an overpotential improvement of 24-28 mV compared to comparative examples 2A, 3A, and 4A.

[0131] Example 8A provides a platinum and ruthenium layer comprising a pre-modified carbon-supported platinum and ruthenium layer and Nafion. TM Performance of the single electrode layer of the ionomer binder. The electrode performance is -0.049V relative to RHE. This demonstrates an overpotential improvement of 38mV compared to comparative examples 2, 3, and 4.

[0132] Therefore, Examples 5A-8A show that carbon-containing electrodes provide significant performance benefits compared to equivalent coating levels in the absence of carbon.

[0133] 2. Full-scale monopolar industrial chlor-alkali batteries 2.1. Experimental setup In a full-scale industrial chlor-alkali pilot cell (FM21, 0.21m) containing a "Type B" single-electrode assembly. 2 The time period during which electrochemical performance is continuously extended (membrane area).

[0134] In each experiment, relative to the standard anodic coating (Chlorcoat) TM The cathode electrode was tested using a membrane (Aciplex™ A4202, AsahiKasei). The cell construction employed the same sealed configuration, compression, and internal configuration for each test.

[0135] The battery operates at 85°C (+ / -2°C) using typical industrial feed materials with NaCl and NaOH concentrations of 3 kA / m. 2 The battery operates at current densities. As is common practice in industrial electrolyzers using liquid electrolyte feed, the voltage output from the cell is normalized to account for minor temperature and concentration fluctuations that occur during testing. Such a strategy is readily apparent to those skilled in the art of operating such batteries.

[0136] 2.2. preparation Comparative Example 3B: The same coating formulation was used to reproduce the above-mentioned comparative example 3A on the "Type B" electrode.

[0137] Example 5B: The same coating formulation was used to reproduce Example 5A above on the "Type B" electrode.

[0138] Example 9B: This embodiment is produced on a "Type B" electrode as described below.

[0139] This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon, ruthenium, and palladium. In this embodiment, ruthenium and palladium are co-deposited.

[0140] The coating was produced by first dissolving ruthenium(III) chloride crystals in glacial acetic acid to a concentration of 33 g Ru / L using ultrasound for at least 10 minutes. Soluble palladium acetate crystals at a concentration of 3.86 g Pd / L were then added and dissolved using ultrasound. A slurry was produced by adding carbon black powder (Cabot Vulcan XC-72R) at a concentration of 8.71 g C / L to the salt solution and dispersing it using ultrasound for at least 30 minutes.

[0141] The resulting composition was 2:0.9:0.1 C:Ru:Pd (molar ratio) (by weight, 72.41% Ru, 8.47% Pd, and 19.12% C).

[0142] It was sprayed onto the pre-sandblasted electrode in multiple layers, with intermediate drying at 180°C for 2 minutes between coatings, followed by heat treatment in air at 450°C for 12 minutes. The coating was repeated until the coating level reached 10-12 g Ru / m². 2 , such as measurements taken via calibrated XRF.

[0143] Example 10B: This embodiment is produced on a "Type B" electrode as described below.

[0144] This embodiment illustrates an electrode having an electrocatalytic layer comprising carbon, ruthenium, and platinum. In this embodiment, ruthenium and platinum are co-deposited.

[0145] The coating was produced by first dissolving ruthenium(III) chloride crystals in glacial acetic acid to a concentration of 33 g Ru / L using ultrasound for at least 10 minutes. A solution of dihydrohexachloroplatinic acid (150 g / L, in 20% HCl) at a concentration of 7.08 g Pt / L was added to the solution. Carbon black powder (Cabot Vulcan XC-72R) at a concentration of 8.71 g C / L was added to the salt solution and dispersed ultrasonically for at least 30 minutes to produce a slurry. The resulting composition was 2:0.9:0.1 C:Ru:Pt (molar ratio) (by weight, 67.63% Ru 14.50% Pt 17.86% C).

[0146] It is sprayed in multiple layers onto the pre-sandblasted electrode, with intermediate drying at 180°C for 2 minutes between layers, and then heat-treated in air at 450°C for 12 minutes between layers. The coating is repeated until the coating level reaches 10-12 g Ru / m². 2 , such as measurements taken via calibrated XRF.

[0147] 2.3. result Table 2 provides the normalized battery voltage applied to each embodiment of the “Type B” electrode.

[0148] Table 2: <![CDATA[ Example ]]> <![CDATA[ composition ]]> <![CDATA[ Normalized battery voltage (V) ]]> Comparative Example 3B Carbon-free Pt:Ru coating -2.934 Example 5B 2:1 C:Ru (molar ratio) - Heat treated to 350℃ -2.857 Example 9B 2:0.9:0.1 C:Ru:Pd (molar ratio) - heat treated to 450℃ -2.820 Example 10B 2:0.9:0.1 C:Ru:Pt (molar ratio) - heat treated to 450℃ -2.840 Comparative Example 3B provides the performance of a typical carbon-free industrial platinum-ruthenium coating.

[0149] Example 5B provides the performance of a carbon-loaded ruthenium coating (molar composition 2:1 C:Ru). The normalized cell voltage is improved by 0.077 V compared to Comparative Example 3B. This is slightly larger than, but consistent with, the result of the equivalent example in a single-electrode potential test using a "Type A" electrode, and demonstrates the advantage of using carbon-loaded ruthenium to enhance electrode performance on an industrial scale.

[0150] Example 9B provides the performance of a coating containing carbon, ruthenium, and palladium. In the same battery, the normalized battery voltage is improved by 0.114 V compared to Comparative Example 3B, and by 0.037 V compared to Example 5B.

[0151] Example 10B provides the performance of a coating containing carbon, ruthenium, and platinum. In the same cell, the normalized cell voltage is improved by 0.094V compared to Comparative Example 3B, and in the same cell, the normalized cell voltage is improved by 0.017V compared to Example 5B.

[0152] These examples demonstrate that further improvements can be made using a mixture of metal and carbon.

[0153] 3. Full-scale bipolar industrial chlor-alkali batteries 3.1. Experimental setup The duration of sustained electrochemical performance was measured in a full-scale industrial chlor-alkali electrolyzer with a "C-type" electrode (supplier: INOVYN Technologies Ltd).

[0154] In each case, the cathode comprises an expanded nickel electrode, each measuring approximately 1.2m × 1.2m, and is coated as described below.

[0155] The coated electrodes are soldered to full-scale BICHLOR™ cathode disks, with two electrodes soldered side-by-side using standard manufacturing techniques. The approximate projected electrode area for each finished disk is 2.9 m². 2 .

[0156] A chlor-alkali module for the BICHLOR™ electrolyzer is constructed by bolting the cathode disk formed above to the BICHLOR™ anode disk, with a membrane septum between the anode and cathode electrodes. The membrane is sealed into the module by two PTFE-protected EPDM rubber gaskets (supplier INOVYN Technologies Ltd) located around the periphery of the membrane (one gasket on each side of the membrane), and pressed between the flanges of the membrane and the disk by twisted bolts inserted into the two flanges, the membrane, and the gaskets. Each anode disk contains two coated, expanded metal anode electrode meshes coated with the standard INOVYN “Chlorcoat™” anode coating, which are welded side-by-side to the anode disk using standard manufacturing techniques for these disks. The design of the anode, cathode, and module components is described in detail in U.S. Patent 6,761,808 B1.

[0157] The electrolyzer contains 14 modules of the aforementioned type, configured as described below. During operation, the electrolyzer is fed with approximately 30% NaOH and approximately 300 g / L of feed brine. The discharged brine and NaOH concentrations are approximately 220 g / L and approximately 32%, respectively. The electrolyzer operates at a liquid outlet temperature of 87°C, a gas pressure of 235 mbar chloride and 250 mbar hydrogen, and a pressure of 5.5 kA / m³. 2 to 6 KA / m 2 Operating at current densities between [specific values].

[0158] 3.2. preparation Example 3C: Twenty cathodes were produced using the same coatings and methods as in Examples 3A and 3B.

[0159] As described above, electrodes are welded in pairs to the cathode disk and then connected to the anode as described above to form 10 modules. In five modules, the membrane separator used is Aciplex F6801 supplied by Asahi Kasei Corporation of Japan (“Module Example 3C1” in Table 3 below), while in the other five finished modules, the separator used is Flemion F8080 supplied by Asahi Glass Co. Ltd of Japan (“Module Example 3C2” in Table 3 below).

[0160] Example 10C: Eight cathodes were produced using the same coating and method as in Example 10B. As described above, electrodes were welded in pairs to the cathode disks and then connected to the anodes, also as described above, to form four modules. In two modules, the membrane separators used were Aciplex F6801 supplied by Asahi Kasei Corporation of Japan (“Module Example 10C1” in Table 3 below), while in the other two modules, the separators used were Flemion F8080 supplied by Asahi Glass Co. Ltd of Japan (“Module Example 10C2” in Table 3 below). All 14 modules are built into the BICHLOR™ chlor-alkali electrolyzer and operate simultaneously.

[0161] 3.3. result Table 3 provides the average voltage for each module type at startup.

[0162] Table 3: Cathode Start-up Performance *Voltage normalized to 6KA / m2 90°C, 32% NaOH concentration and 235 mbar chloride pressure The table shows that at 6.0KA / m 2 At current densities, compared among modules with the same film type, the average startup voltage of modules containing co-deposited carbon, ruthenium, and platinum coatings is improved by 65-90 mV compared to the average startup voltage of modules with carbon-free ruthenium and platinum coatings.

[0163] At 5.5KA / m 2 Up to 6.0KA / m 2 After two months of continuous operation at the given current density, the voltages of all four embodiments were the same as those measured at startup, indicating that the cathode was stable and maintained an advantageously low voltage.

[0164] 4. Stability during startup and shutdown 4.1. Experimental setup In standard single-cell mounting and testing, an expanded cathode mesh (“D” type electrode) with a coating thickness of 0.15 mm was used at 100 cm. 2 Micro-pilot tests were conducted at (membrane electrode area) and routinely used to determine the effect of multiple consecutive shutdowns on the performance of the cathode coating.

[0165] In normal factory operation, industrial electrolyzers are not frequently shut down, and therefore the tests described herein allow for multiple shutdowns over relatively short periods of time to simulate the effects that typically accumulate over several years of operation in a factory.

[0166] The usual practice is to shut down the bipolar industrial chlor-alkali electrolyzer while maintaining a small "forward" current (the magnitude of which depends on the membrane area and the number of modules in the electrolyzer) to prevent reverse current flow between adjacent cells and to protect the electrode coatings (especially the cathode coating) from damage. Therefore, another aspect of the test involves shutting down the cell without this protection and allowing reverse current flow by externally short-circuiting the anode and cathode electrodes (which occurs spontaneously in bipolar cells when the anode and cathode are in electrical contact). Under these test conditions, coatings that cannot withstand reverse current will degrade, and this will be clearly seen in the cell voltage, which will increase (negatively).

[0167] The test cell contained a titanium anode frame with square cutouts, in which an expanded titanium mesh was welded and secured with a Cholecoat. TMA standard anode coating is applied, which is resistant to reverse current (and therefore does not affect the test results). Using the same nickel cathode frame with notches, a mechanical spring is used to hold the coated cathode mesh in place against the membrane and maintain electrical contact. The cell is completed by clamping the anode and cathode frames (with mesh) together with two gaskets and a standard chlor-alkali industrial membrane (Flemion F8080, Asahi Glass). In this configuration, current is collected from the edges of both frames.

[0168] Additional plates are constructed on either side of the anode and cathode frames to provide reactant feed and product collection, and heating is provided using resistance heaters. The two plates are mounted at the ends of the cell, which are used to press the assembly to a predetermined torque using tie rods.

[0169] A regulated flow of brine at a concentration of 250 g / kg was fed into the anode chamber of the battery to maintain an outlet concentration of 185 g / kg. Softened water at a regulated flow rate was fed into the cathode chamber to maintain an outlet concentration of 315 g / kg. Tests were conducted at 85°C.

[0170] Experiments to evaluate the stability of the coating were conducted by first running the cathode sample for several days until it reached 4 kA / m. 2 A stable battery voltage was obtained under a forward current density. Then, the DC power supply was turned off, and the anode and cathode were externally short-circuited for 1 hour using a switch. Under these conditions, the battery voltage rapidly rose to 0V, and a spontaneous reverse current (flowing from cathode to anode) was observed. The forward current was then reconnected, and a current of 4kA / m was applied. 2 Keep the battery running for 24 hours until the battery voltage stabilizes again. Then disconnect the current and short-circuit the battery again, repeating this process 10-30 times while monitoring the stable battery voltage at 4kA / m. 2 The change in battery voltage by 300mV relative to the start of the test (increasing the negative value) indicates severe damage to the cathode coating, where the electrode eventually behaves as if it were composed of uncoated nickel.

[0171] Therefore, the unstable coating exhibits significant voltage changes during the shutdown period of reverse current flow.

[0172] 4.2. preparation Comparative Example 4D: Electrodes were produced on “D-type” electrodes using the same coatings and methods as in Example 4A to produce Comparative Example 4D.

[0173] Example 5D: Electrodes of Example 5D were produced on “D-type” electrodes using the same coatings and methods as in Examples 5A and 5B.

[0174] 4.3. result Figure 1 Table 4 shows the battery voltage relative to the number of shutdown cycles for Comparative Examples 4D and 5D. Figure 1 A summary of the data presented.

[0175] Comparative Example 4D demonstrates a starting battery voltage of -2.85V, while Example 5D demonstrates an improvement of 30mV, with a battery voltage of -2.82V. This proves that, with the same coating weight on the "D-type" electrode, the ruthenium-carbon coating is more active than the ruthenium coating alone.

[0176] Comparative Example 4D shows a significant change in battery voltage during just 7 shutdown cycles, decreasing to -3.04V (equivalent to a battery voltage change of 190mV).

[0177] On the other hand, Example 5D showed no significant change in battery voltage during 43 shutdown cycles. This example demonstrates that the carbon-ruthenium coating exhibits significantly better shutdown resistance.

Claims

1. An electrode assembly for producing hydrogen, the assembly comprising: i) Anode structure, which includes an anode located within the electrolysis chamber, ii) A cathode structure comprising a cathode located within an electrolytic chamber containing an alkali metal hydroxide solution. Its features The cathode comprises: a) A conductive metal substrate, wherein the metal substrate is stainless steel, low-carbon steel, nickel, or copper, and b) An electrocatalytic layer on the substrate, the layer comprising at least one metal supported on a conductive carrier material, wherein a. The electrocatalytic layer comprises 0.2-10 vol% of at least one metal, and said at least one metal is selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum. b. The electrocatalytic layer comprises 90-99.8% by volume of the conductive support material, wherein the conductive support material is formed of particles with an average particle size of less than 5 µm (5 micrometers), and these particles are not metal particles, and the conductive support material has a particle size of 50 μm. 2 / g to 2000m 2 / g surface area, and c. The electrocatalyst layer has a thickness of 0.5-100 µm and a porosity in the form of a three-dimensional network of channels between the deposited particles, the channels having an average diameter of 5-500 nm.

2. The electrode assembly according to claim 1, wherein the at least one metal comprises at least one platinum group metal.

3. The electrode assembly of claim 2, wherein the at least one metal comprises ruthenium.

4. The electrode assembly of claim 3, wherein the at least one metal comprises ruthenium and platinum.

5. The electrode assembly according to claim 1, wherein the conductive carrier material comprises a conductive carbon material.

6. The electrode assembly according to claim 1, wherein the surface area of ​​the conductive carrier material is 200-1000 m². 2 / g.

7. The electrode assembly of claim 1, wherein the conductive carrier material is formed of particles with an average particle size of less than 1 µm (1 micrometer).

8. The electrode assembly of claim 7, wherein the conductive carrier material is formed of particles with an average particle size of 10-250 nanometers.

9. The electrode assembly of claim 7, wherein the conductive carrier material is formed of particles with an average particle size of 20-100 nanometers.

10. The electrode assembly of claim 1, wherein the cathode further comprises a binder.

11. The electrode assembly of claim 10, wherein the cathode comprises a binder that has been coated with the electrocatalytic layer.

12. The electrode assembly of claim 1, wherein the cathode comprises two or more electrocatalytic layers as defined in the preceding claims, but wherein the deposited layers are different in composition.

13. The electrode assembly according to any one of claims 1-12, for producing hydrogen and halogens, wherein the electrolytic chamber of the anode structure contains a solution of alkali metal halides.

14. The electrode assembly according to any one of claims 1-12, for producing hydrogen and oxygen, wherein the electrolytic chamber of the anode structure contains a solution of alkali metal hydroxide.

15. A modular or filter press electrolyzer comprising a plurality of electrode assemblies as described in any one of claims 1-12.

16. The modular or filter press electrolyzer of claim 15, comprising 5-300 electrode assemblies.

17. A method for electrolysis, the method comprising electrolyzing in an electrode assembly according to any one of claims 1-12 to produce hydrogen.

18. The method of claim 17, wherein the method comprises electrolyzing in a modular or filter press electrolyzer containing a plurality of the electrode assemblies to produce hydrogen.

19. Use of an electrocatalytic layer on an electrode, said electrode comprising a) A conductive metal substrate, wherein the metal substrate is stainless steel, low-carbon steel, nickel, or copper, and b) An electrocatalytic layer on the substrate, the layer comprising at least one metal supported on a conductive carrier material, wherein a. The electrocatalytic layer comprises 0.2-10 vol% of at least one metal, and said at least one metal is selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum. b. The electrocatalytic layer comprises 90-99.8% by volume of the conductive support material, wherein the conductive support material is formed of particles with an average particle size of less than 5 µm (5 micrometers), and these particles are not metal particles, and the conductive support material has a particle size of 50 μm. 2 / g to 2000m 2 / g surface area, and c. The electrocatalyst layer has a thickness of 0.5-100 µm and a porosity in the form of a three-dimensional network of channels between the deposited particles, the channels having an average diameter of 5-500 nm. To provide at least one of the following: i) The reduced overpotential of the electrode. ii) The overpotential of the electrode stabilized during the extended operating cycle, and iii) Improved reverse current tolerance of the electrodes.

20. The use according to claim 19, wherein the electrode is a cathode in a method for producing hydrogen from a cathode.

21. The use according to claim 20, wherein the method of producing hydrogen from the cathode is a method of producing hydrogen from an alkali metal hydroxide at the cathode and (1) producing halogen from an alkali metal halide or (2) producing oxygen from an alkali metal hydroxide at the anode.

22. A method for preparing a cathode to be used in a method for electrolyzing alkali metal hydroxides to produce hydrogen, comprising: i) Production electrode, the electrode comprising a) A conductive metal substrate, wherein the metal substrate is stainless steel, low-carbon steel, nickel, or copper, and b) An electrocatalytic layer on the substrate, the layer comprising at least one metal supported on a conductive carrier material, wherein a. The electrocatalytic layer comprises 0.2-10 vol% of at least one metal, and said at least one metal is selected from platinum group metals, rhenium, nickel, cobalt, and molybdenum. b. The electrocatalytic layer comprises 90-99.8% by volume of the conductive support material, wherein the conductive support material is formed of particles with an average particle size of less than 5 µm (5 micrometers), and these particles are not metal particles, and the conductive support material has a particle size of 50 μm. 2 / g to 2000m 2 / g surface area, and c. The electrocatalyst layer has a thickness of 0.5-100 µm and a porosity in the form of a three-dimensional network of channels between the deposited particles, the channels having an average diameter of 5-500 nm. and ii) The electrode is supplied as a cathode in a method for electrolyzing alkali metal hydroxides to produce hydrogen.

23. The method according to claim 22, wherein the method for electrolyzing alkali metal hydroxides to produce hydrogen is a method for producing hydrogen from the cathode and (1) producing halogens from alkali metal halides or (2) producing oxygen from alkali metal hydroxides at the anode.

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