Membrane electrode assembly

Abstract

A membrane electrode assembly (MEA) for producing hydrogen in a water electrolyzer is provided. The MEA comprises a polymer electrolyte membrane (REM), a cathode comprising a cathode catalyst on a first side of the REM, an anode comprising an anode catalyst on a second side of the REM, and a platinum-ruthenium (Pt-Ru) catalyst disposed on the second side of the REM for electrochemically converting hydrogen gas into hydrogen cations during use. The Pt-Ru catalyst is in electrical contact with the anode and in ionic contact with the REM.

Description

[Technical Field]

[0001] The present invention relates to a membrane electrode assembly (MEA) for a hydrogen electrolyzer. [Background technology]

[0002] As demand for renewable energy sources increases, so does the need to produce hydrogen in a safe and efficient manner. Hydrogen is typically obtained from the electrolysis of water using a water electrolysis cell. This is an electrochemical device that dissociates water to produce hydrogen and oxygen gases. The most commonly used electrolyzers incorporate a polymer electrode membrane (PEM). As shown in FIG. 1, a PEM water electrolysis cell comprises a cathode, an anode, and a polymeric electrolyte. A polymer electrolyte is disposed between the cathode and anode and transports ions between the electrodes while blocking the transport of electrons. Additionally, to ensure both electronic and ionic conductivity, the catalyst is embedded in (or surrounded by) the polyelectrolyte while remaining below the percolation threshold. This ensures that ions can enter and exit the polyelectrolyte.

[0003] During operation of a PEM water electrolysis cell, water is electrochemically oxidized to oxygen gas at the anode catalyst, and hydrogen cations (protons) migrate through the polymer electrolyte to the cathode catalyst, where they are electrochemically reduced to hydrogen gas. Protons are transported from the anode to the cathode by an electric field applied across the PEM. The rate of water consumption, and hence the rate of hydrogen and oxygen evolution, is governed by Faraday's law, such that an increase in current through the cell causes a corresponding increase in gas evolution and water consumption. PEM electrolysis is advantageous over other types of electrolysis because the hydrogen produced is highly pure, hydrogen can be produced under pressure, and it is more efficient than other forms of electrolysis. However, efficiency is limited by the resistance of the membrane, especially at high current densities. Voltage loss (inefficiency) is directly proportional to resistance (voltage loss = current * resistance).

[0004] A problem associated with conventional PEM electrolysers is that hydrogen can diffuse across the membrane to the anode side and mix with oxygen to form a flammable or explosive mixture. This occurs especially when the hydrogen is under pressure. This hydrogen diffusion problem is typically ameliorated by using thick membranes (greater than 125 μm), preferably made from perfluorosulfonic acid (PSFA) polymers such as Nafion® or Aquivion®, to effectively reduce hydrogen diffusion through the membrane. However, the use of such thick films results in large ohmic resistance, especially at 1 A.cm -2 The efficiency of the electrolytic cell decreases at current densities above this value.

[0005] Several known techniques are utilized to minimize hydrogen buildup in the anode compartment.

[0006] For example, WO 2019 / 009732 discloses supplying humidified air to the anode (oxygen) compartment of a PEM electrolysis cell to dilute any diffused hydrogen and maintain an atmosphere below the lower explosive limit (LEL) of approximately 4 mol% hydrogen-air mixture. This minimizes the risk of generating flammable or explosive gas mixtures during operation of the electrolysis cell. Water is applied to the cathode (hydrogen) compartment and diffuses across the membrane to the anode catalyst where it is oxidized to protons, oxygen, and electrons. However, a drawback of this process is that it relies on the diffusion of water across the membrane to the anode, which can limit the current density.

[0007] M Schalenbach and D Stolten, "High-pressure water electrolysis: electrochemical mitigation of product gas crossover," Electrochimica Acta, 156 (2015), pp. 321-327, disclose embedding platinum in PEMs to prevent hydrogen diffusion. The platinum, which is not electrically connected to either electrode, acts as a recombination catalyst, converting hydrogen and oxygen gases within the membrane into water. However, this approach has drawbacks. Because the platinum must be embedded in the membrane, the membrane must be specially cast around the catalyst. Commercially available membranes cannot be used. Therefore, the cost of manufacturing and maintaining such catalyst-embedded electrolysers is higher than that of conventional PEM electrolysers. Additionally, because hydrogen is under pressure and oxygen is typically not, oxygen and hydrogen gas do not diffuse at the same rate. If the oxygen diffusion rate falls below a threshold relative to the hydrogen diffusion rate, the amount of hydrogen in the PEM may exceed the capacity of the recombination catalyst, potentially resulting in hydrogen accumulation in the anode compartment.

[0008] N. Briguglio, F. Pant, S. Suracusano, and A. Arico, "Improvement of the performance of a PtCo recombination catalyst to reduce the H2 concentration in the O2 stream of a PEM electrolysis cell in the presence of thin films and high differential pressures," Electrochimica Acta 344 (2020) 36153, also discloses the use of a recombination catalyst (based on a PtCo alloy) placed in the anode compartment to recombine hydrogen and oxygen. A drawback of this system is that rebonding does not work very well in wet conditions. Furthermore, Co tends to leach from the PtCo alloy, which can limit the catalyst life and adversely affect the operation of the electrolyzer. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, there is a need for a PEM water electrolyzer that alleviates at least some of the aforementioned problems. [Means for solving the problem]

[0010] According to a first aspect of the present invention, there is provided a membrane electrode assembly (MEA) for producing hydrogen in a water electrolyzer, the MEA comprising a polymer electrolyte membrane (PEM); a cathode comprising a cathode catalyst on a first side of the PEM; an anode comprising an anode catalyst on the second side of the PEM; and a platinum-ruthenium (Pt—Ru) catalyst disposed on a second side of the PEM for electrochemically converting hydrogen gas into hydrogen cations during use, the Pt—Ru catalyst being in electrical contact with the anode and in ionic contact with the PEM.

[0011] The advantage of the MEA is that it can prevent hydrogen from diffusing from the PEM to the second (anode) side and combining with oxygen to form a flammable or explosive mixture, especially during high-pressure electrolysis. Because the hydrogen is removed catalytically, the thick membranes used in conventional electrolysers to limit hydrogen diffusion are not required, and thinner membranes can be used, increasing the efficiency of the electrolyser.

[0012] The MEA may be suitable for high pressure electrolysis, ie for producing hydrogen in a water electrolyser at a pressure of at least 30 bar.

[0013] The incorporation of alloyed platinum and ruthenium into the catalyst gives it an advantage over other hydrogen oxidation catalysts such as platinum, as it does not oxidize at the operating potential of the electrolyzer. When platinum is brought into contact with an anode catalyst (typically an Ir-based catalyst such as IrO2), the potential of the hydrogen oxidation catalyst increases, potentially causing oxidation to platinum oxide. Metal oxides do not electrochemically reduce hydrogen, resulting in deactivation of the catalyst. However, when Ru and Pt are alloyed, the Ru reacts with the Pt to keep it in a neutral oxidation state, preserving its electrochemical reactivity.

[0014] The PEM can have a thickness of 50 μm or less. For example, the PEM can have a thickness of less than 50 μm, 10 μm to 50 μm, 10 μm to 45 μm, 10 μm to 40 μm, 10 μm to 35 μm, or 10 μm to 25 μm.

[0015] The MEA may further comprise an anode channel in fluid communication with the anode and configured to direct water to the anode and receive oxygen from the anode in use, and a cathode channel in fluid communication with the cathode and configured to receive hydrogen from the cathode in use, and the Pt-Ru catalyst may be disposed between the PEM and the anode channel and may be configured to reduce the amount of hydrogen gas that flows from the PEM into the anode channel in use.

[0016] Oxygen is produced at the anode catalyst and transported from the PEM through the anode channels as a product of the electrolysis process. The Pt-Ru catalyst effectively forms a barrier that prevents hydrogen from diffusing from the PEM into the anode channel and combining with oxygen to form a flammable mixture.

[0017] The Pt-Ru catalyst may be (i) dispersed in the anode and / or (ii) layered between the PEM and the anode.

[0018] Dispersing the Pt-Ru catalyst in the anode catalyst and / or forming a layer between the PEM and the anode catalyst allows the Pt-Ru catalyst to effectively act as a barrier between the PEM and the anode channel. Furthermore, by mixing or dispersing the Pt-Ru catalyst into the anode catalyst, both catalysts can be applied to the PEM in a single step without disrupting the existing MEA manufacturing process.

[0019] Pt-Ru catalyst: 0.005 to 0.5 mg / cm 2 , preferably 0.02 to 0.1 mg / cm 2 can be present in an amount of This corresponds to an amount of about 0.2 to 25 wt %, or more narrowly about 1 to 5 wt %, of the anode catalyst loading. These amounts of Pt-Ru are effective in preventing hydrogen from diffusing from the PEM into the anode channel.

[0020] Platinum can be present in the Pt-Ru catalyst in an amount of 10-90 wt%, 30-70 wt%, or about 50 wt%. Similarly, ruthenium can be present in the Pt-Ru catalyst in an amount of 90-10 wt%, 70-30 wt%, or about 50 wt%.

[0021] Amounts of Pt and Ru within these ranges optimize the level of hydrogen oxidation activity, resulting in extended catalyst life, while maintaining a minimal level of Pt oxidation.

[0022] According to a second aspect of the present invention, there is provided a method for manufacturing an MEA as defined above, the method comprising the steps of: Coating a first side of a polymer electrolyte membrane (PEM) with a cathode catalyst; coating a second side of the PEM with an anode catalyst; applying a Pt-Ru catalyst to the second side of the PEM such that the Pt-Ru catalyst is in electrical contact with the anode catalyst and in ionic contact with the PEM.

[0023] The method may further include fixing the anode channel on the anode catalyst such that the anode channel is in fluid communication with the anode catalyst, fixing the cathode channel on the cathode catalyst such that the cathode channel is in fluid communication with the cathode catalyst, and applying a Pt-Ru catalyst to a second side between the PEM and the anode channel.

[0024] The applying step includes: (i) dispersing a Pt—Ru catalyst in a flowable anode catalyst to form a mixture and coating the mixture on a PEM; and / or (ii) forming a layer of Pt-Ru catalyst on the PEM prior to coating the second side of the PEM with the anode catalyst;

[0025] The catalyst is 0.005 to 0.5 mg / cm 2 , preferably 0.02 to 0.1 mg / cm 2 can be applied in an amount of

[0026] Platinum can be present in the Pt-Ru catalyst in an amount of 10-90 wt%, 30-70 wt%, or 50 wt%. Similarly, ruthenium can be present in the Pt-Ru catalyst in an amount of 90-10 wt%, 70-30 wt%, or 50 wt%.

[0027] The Pt-Ru catalyst of the MEA may consist essentially of platinum and ruthenium.

[0028] According to a third aspect of the present invention, there is provided the use of an MEA as defined above for producing hydrogen.

[0029] The advantages of the second and third aspects of the present invention are similar to those described above in relation to the first aspect of the present invention, as will be appreciated by those skilled in the art.

[0030] The present invention will be better understood in light of the following examples and the accompanying drawings, which are given in an illustrative manner only and should not be construed as limiting. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view of a prior art MEA for producing hydrogen in a water electrolyzer, showing H2 permeation from the cathode side to the anode side of the MEA. [Figure 2] 1 is a cross-sectional view of an MEA for producing hydrogen in a water electrolyzer according to the present invention, where H2 is prevented from diffusing from the PEM into the anode channel by a Pt-Ru catalyst layer. [Figure 3] FIG. 3 is a schematic diagram of the MEA of FIG. 2 showing the relative positions of the anode layer, Pt—Ru catalyst layer, PEM, and cathode layer. [Figure 4] 1 is a graph showing the improved efficiency of an electrolyzer with an MEA according to the invention compared to an electrolyzer with an MEA of the prior art. [Figure 5] 1 is a cell IV curve showing current density (A cm) versus cell voltage (V) using (i) a standard Nafion® N115 perfluorosulfonic acid (PFSA) membrane having a thickness of 127 μm, and (ii) a membrane including a Ru—Pt catalyst layer according to the present disclosure. [Figure 6] 1 is a graph showing hydrogen permeation through (i) a standard Nafion® N115 perfluorosulfonic acid (PFSA) membrane having a thickness of 127 μm, and (ii) a membrane including a Ru—Pt catalyst layer according to the present disclosure at hydrogen differential pressures of 10 bar, 20 bar, and 30 bar. DETAILED DESCRIPTION OF THE INVENTION

[0032] As used in this specification and the appended claims, unless the context requires otherwise, "comprise" or variations such as "comprises" or "comprising" will be understood to mean the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0033] As used herein, the term "about" in connection with amounts expressed as weight percent means that the stated amount can vary ±10% of the stated amount. For example, about 90 wt% means 90±9 wt%, and about 0.1 wt% means 0.1±0.01 wt%. When used in connection with a range, the term "about" applies to all values ​​within the range.

[0034] As used herein, with respect to components of a composition, alloy, or mixture, the term "consisting essentially of" means that the composition, alloy, or mixture contains the indicated components in the specified proportions, and may contain minor additional components in amounts of less than 1 wt. %, based on the total weight of the composition, alloy, or mixture, provided that the additional components do not substantially alter the reactivity of the composition, alloy, or mixture.

[0035] In a first aspect, the present disclosure provides a membrane electrode assembly (MEA) for producing hydrogen in a water electrolyzer (electrochemical hydrogen generator), particularly at high pressure. High pressure electrolysis is typically carried out at pressures above about 30 bar, for example, from 30 bar to 200 bar, from 50 bar to 200 bar, from 75 bar to 200 bar, or even above 200 bar. As shown in the embodiment depicted in Figures 2 and 3, the MEA (10) comprises a polymer electrolyte membrane (PEM) (12), a cathode (14) comprising a cathode catalyst (also referred to as a hydrogen generation catalyst) on a first side (16) of the PEM (12), an anode (18) comprising an anode catalyst (also referred to as an oxygen generation catalyst) on a second side (20) of the PEM (12), and a platinum-ruthenium (Pt-Ru) catalyst (22) (also referred to as a hydrogen oxidation catalyst) disposed on the second side (20) of the PEM (12). The Pt-Ru catalyst (22) is suitable for electrochemically converting hydrogen gas to hydrogen cations when the MEA (10) is in use. The Pt-Ru catalyst (22) is in electrical contact with the anode (18) through which it operatively receives electrical energy for the electrochemical reaction. The Pt-Ru catalyst (22) is in ionic contact with the PEM (12) and transports the hydrogen cations produced in the reaction to the cathode (14), where they can be converted to hydrogen gas.

[0036] The Pt-Ru catalyst (22) provides a barrier that prevents hydrogen from exiting the PEM (12) on the second (anode) side (20). This is especially important when hydrogen is produced at high pressure on the first (cathode) side (16), because high pressure can increase the rate at which hydrogen diffuses through the membrane toward the anode side (20). By preventing hydrogen from permeating across the membrane during high-pressure electrolysis, thinner PEMs can be used without the risk of hydrogen mixing with oxygen in the anode compartment and creating a flammable or explosive mixture. The ability to use thinner membranes in high voltage electrolysis processes is desirable as it improves efficiency.

[0037] The MEA (10) may further comprise an anode channel (24) in fluid communication with the anode (18) on the second side (20) of the PEM (12). The anode channel (24) may be configured to conduct water for the electrolysis reaction to the anode (18) and to receive oxygen produced during the electrolysis of water from the anode (18). In this manner, the anode channels (24) can act as conduits for transporting water (liquid and / or vapor) and oxygen to and from the catalytic surface of the anode (18). Similarly, the MEA (10) may further comprise a cathode channel (26) in fluid communication with the cathode (14) on the first side (16) of the PEM (12). The cathode channel (26) may be configured to receive hydrogen produced at the cathode (14) in use by electrolysis of water and deliver it to a reservoir for storage. A Pt-Ru alloy catalyst (22) may be disposed on the second side (20) between the PEM (12) and the anode channel (24) and may be configured to reduce the amount of hydrogen gas that flows from the PEM (12) into the anode channel (24) during use.

[0038] The Pt—Ru catalyst (22) may be dispersed in the anode (18) and / or may form a layer between the PEM (12) and the anode (18). In a preferred embodiment, the Pt-Ru catalyst (22) can simply be dispersed in the anode (18) catalyst solution or slurry, and the dispersion can be applied to the PEM (12) by any number of conventional means known in the art (e.g., spraying, printing, etc.). In another embodiment, the Pt—Ru catalyst (22) can be coated on the anode side (20) of the PEM (12) before the anode (18) catalyst is applied to the membrane (12). Alternatively, the Pt-Ru catalyst (22) may be applied to the completed (3-layer) MEA on top of the anode catalyst. The only requirement is that the Pt-Ru catalyst (22) be in electrical and ionic contact with the anode catalyst and PEM, respectively. The MEA may further comprise an anode diffusion layer (28) (also called an anode porous transport layer) between the anode (18) and the anode channel (24), and a cathode diffusion layer (30) (also called a cathode porous transport layer) between the cathode (14) and the cathode channel (26).

[0039] The Pt-Ru catalyst (22) was approximately 0.001–1 mg / cm 2 , about 0.005~0.5mg / cm 2 , about 0.01~0.3mg / cm 2 or approximately 0.02 to 0.1 mg / cm 2 can be present in the MEA (10) in an amount of This may correspond to an amount of about 0.05-50 wt%, about 0.25-25 wt%, about 0.5-15 wt%, or about 1-5 wt% of the anode catalyst loading, respectively.

[0040] Platinum can be present in the Pt-Ru catalyst (22) in an amount of about 10-90 wt%, about 20-80 wt%, about 30-70 wt%, about 40-60 wt%, or about 50 wt%. Similarly, ruthenium can be present in the Pt-Ru catalyst in an amount of about 90-10 wt%, about 80-20 wt%, about 70-30 wt%, 60-40 wt%, or about 50 wt%. Preferably, Pt and Ru are each present in the Pt-Ru catalyst in an amount of about 50 wt%. The Pt-Ru alloy catalyst (22) may consist essentially of platinum and ruthenium.

[0041] As shown in Figure 4, prior art water electrolyzers with PEMs thicker than 125 μm operate at stack efficiencies of approximately 65-70% (high heating value (HHV)). Electrolyzers incorporating MEAs of the present invention can operate at efficiencies of about 82% at high current densities and high pressures using membranes about 50 μm thick without hydrogen accumulation in the anode channels. This efficiency improvement can be even higher if thinner membranes are used. For example, an MEA of the present disclosure can comprise a membrane having a thickness of 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, or 25 μm or less. The membrane can have a thickness of 10 μm to 75 μm, 10 μm to 50 μm, 10 μm to 45 μm, 10 μm to 40 μm, 10 μm to 35 μm, or 10 μm to 25 μm.

[0042] In a second aspect, the present disclosure provides a method for producing the above-described MEA. The method includes coating a first side of a polymer electrolyte membrane (PEM) with a cathode catalyst to form a cathode, coating a second side of the PEM with an anode catalyst to form an anode, and applying a Pt-Ru catalyst to the second side of the PEM such that the Pt-Ru catalyst is in electrical contact with the anode catalyst and in ionic contact with the PEM.

[0043] The method may further include fixing the anode channel on the anode catalyst such that the anode channel is in fluid communication with the anode catalyst, fixing the cathode channel on the cathode catalyst such that the cathode channel is in fluid communication with the cathode catalyst, and applying a Pt-Ru catalyst to a second side between the PEM and the anode channel. The anode and cathode channels can be immobilized by conventional means known in the art. As described above, the Pt-Ru catalyst can be applied to the second side of the PEM by dispersing the Pt-Ru catalyst in a flowable anode catalyst (e.g., an anode catalyst solution or slurry) to form a mixture and then coating the mixture onto the PEM. Alternatively or additionally, the Pt-Ru catalyst may be applied to the PEM prior to coating the second side of the PEM with the anode catalyst, such that the Pt-Ru catalyst forms a layer between the PEM and the anode catalyst. The Pt-Ru catalyst can be applied to the PEM using conventional methods such as spraying or printing. However, whichever method is used, the Pt-Ru catalyst must be in electrical contact with the anode and in ionic contact with the PEM.

[0044] The catalyst may be applied to the PEM in the amounts defined above for the MEA.

[0045] Platinum and ruthenium may be present in the Pt-Ru catalyst in the amounts defined above for the MEA.

[0046] The present disclosure provides, in a third aspect, the use of an MEA as defined above for producing hydrogen. This use may typically involve providing a water electrolyzer incorporating the MEA, applying electrical energy to the electrolyzer, supplying water to the electrolyzer, and recovering hydrogen produced on the cathode side of the electrolyzer. The oxygen produced on the anode side can be vented or recovered. The hydrogen may be collected in a storage vessel for later use.

[0047] The present invention will now be described in further detail with reference to the following non-limiting examples. [Example]

[0048] Example 1: 0.25 mg of platinum black was deposited onto a 0.5 mm diameter glassy carbon electrode from a water / IPA solution containing a 1:4 ratio of ionomer (dispersed Nafion®) and catalyst. The electrode was rotated at 1600 rpm using a standard rotating disk apparatus, and the potential was scanned from −0.05 V to 1.4 V (vs. SHE) at 0.01 V / s while hydrogen was bubbled over the electrode surface. Initially, the current is 2.3A / cm 2 It rose to. The current remained stable until the voltage reached 0.97 V, after which the current began to decrease to zero.

[0049] Explanation: Platinum oxidizes hydrogen, but the formation of platinum oxide inhibits the oxidation of platinum.

[0050] Example 2: 0.25 mg of a 1:1 ratio platinum / ruthenium black was deposited onto a 0.5 mm diameter glassy carbon electrode from a water / IPA solution containing a 1:4 ratio of ionomer (dispersed Nafion®) and catalyst. The electrode was rotated at 1600 rpm using a standard rotating disk apparatus, and the potential was scanned from −0.05 V to 1.4 V (vs. SHE) at 0.01 V / s while hydrogen was bubbled over the electrode surface. Initially, the current is 1.4A / cm 2 It rose to. The current remains stable until the voltage reaches 0.95 V, after which the current drops to 0.7 A / cm 2 began to decrease slightly. This decrease was due to oxidation of some of the unalloyed Pt / Ru, while the remainder continued to oxidize hydrogen.

[0051] Example 3: The MEA was fabricated by spraying one side of the membrane with a suspension of Pt / C and ionomer (1:1 carbon and ionomer). On the other side is a thin layer of platinum / ruthenium black in a 1:1 ratio (in a suspension containing ionomer and catalyst in a 1:4 ratio). On top of the thin layer, a further layer of iridium oxide (in a suspension containing ionomer and catalyst in a 1:4 ratio) was sprayed onto the membrane. This membrane electrode assembly (MEA) was hot pressed at 140° C. for 1 minute. The MEA was then placed in an electrolyzer cell and an electric current was passed through it until a pressure difference of 5 bar was created across the membrane. The current was continued and the oxygen flow was monitored for hydrogen using a calibrated Hyoptima 720B in-line hydrogen process analyzer connected to a DVM. The experiment was run for over an hour and no hydrogen (above the instrument's detection level) was measured in the oxygen stream.

[0052] Example 4: An MEA was prepared according to Example 3, but without the platinum-ruthenium layer. This MEA was placed in the same electrolytic cell as in Example 3, and the same conditions were repeated. After 1 hour, a Hyoptima 720B in-line hydrogen process analyzer indicated the presence of 0.7% hydrogen in oxygen.

[0053] Example 5: Comparison of cell voltage and current density across an MEA prepared according to the present invention (Oort catalyst coated membrane) and an MEA containing a Nafion® N115 perfluorosulfonic acid (PFSA) membrane with a thickness of 127 μm. The MEA was prepared as follows.

[0054] The catalyst ink was made by mixing a suspension of Nafion® ionomer, catalyst, and solvent (IPA / water mixture) and dispersing in a low intensity ball mill. The catalyst was sprayed onto Nafion® 212 (50 μm thick) using a commercially available ultrasonic atomizer on a heated vacuum plate. The platinum loading of the cathode catalyst was 0.4 mg / cm 2 It was. The loading of the platinum-ruthenium catalyst was 0.2 mg / cm 2 and the loading of the iridium oxide anode catalyst was 2.0 mg / cm 2 It was. The control sample used the same loadings of iridium oxide anode catalyst and platinum cathode catalyst. The same inks were used, but they were sprayed onto Nafion® 115 (125 μm thick).

[0055] The MEA was placed in a high-pressure electrochemical cell (active area 10 cm 2 ) and pressure was applied to the catalyst bed to ensure good contact (10 bar above the operating pressure). Water heated to 60°C was pumped around the oxygen cavity at a flow rate of 100 ml / min. Maximum current was applied for 1 hour to ensure stability, and then the voltage was recorded. The current was reduced and held constant for 1 minute. After 1 minute the voltage was recorded. This process was repeated to measure the voltage at all current densities. The results are presented in Table 1 below and shown in FIG.

[0056] [Table 1]

[0057] Example 6: Hydrogen concentration measurements were made in the anode compartment of the MEA of Example 5 at three different hydrogen differential pressures (10 bar, 20 bar and 30 bar) to determine the extent of hydrogen permeation across the membrane.

[0058] The MEA was placed in a high-pressure electrochemical cell (active area 10 cm 2 ) and pressure was applied to the catalyst bed to ensure good contact (10 bar above the operating pressure). Water heated to 60°C was pumped around the oxygen cavity at a flow rate of 100 ml / min. For crossover measurements, the cell is driven at 1 ampere cm 2 The temperature was then allowed to rise for 40 minutes to ensure equilibrium. A calibrated Hyoptima 720B (level of detection (“LoD”) is approximately 0.4%) was placed in an oxygen waster separation tank and the device was connected to a calibrated digital voltmeter to display the amount of hydrogen in the oxygen.

[0059] The results are presented in Table 2 below and shown in FIG.

[0060] [Table 2]

Claims

1. 1. A membrane electrode assembly (MEA) for producing hydrogen in a water electrolyzer, the MEA comprising: a polymer electrolyte membrane (PEM); a cathode comprising a cathode catalyst on a first side of the PEM; an anode comprising an anode catalyst on a second side of the PEM; a platinum-ruthenium (Pt—Ru) catalyst disposed on the second side of the PEM for electrochemically converting hydrogen gas into hydrogen cations during use, the Pt—Ru catalyst being in electrical contact with the anode and in ionic contact with the PEM.

2. an anode channel in fluid communication with the anode and configured, in use, to conduct water to the anode and receive oxygen from the anode; a cathode channel in fluid communication with the cathode and configured to receive hydrogen from the cathode in use; Furthermore, 2. The MEA of claim 1, wherein the Pt—Ru alloy catalyst is disposed between the PEM and the anode channel and is configured to reduce the amount of hydrogen gas that passes from the PEM into the anode channel during use.

3. 3. The MEA of claim 1 or claim 2, wherein the MEA is suitable for producing hydrogen in a water electrolyser at a pressure of at least 30 bar.

4. 4. The MEA of claim 1, wherein the PEM has a thickness of 50 μm or less.

5. The Pt—Ru catalyst is (i) dispersed in said anode; and / or (ii) forming a layer between the PEM and the anode.

6. The Pt-Ru catalyst has a concentration of 0.005 to 0.5 mg / cm ２ , preferably 0.02 to 0.1 mg / cm ２ 6. The MEA of claim 1, wherein the MEA is present in an amount of

7. 7. The MEA of any one of claims 1 to 6, wherein the platinum is present in the Pt-Ru catalyst in an amount of 10 to 90 wt%, 30 to 70 wt%, or 50 wt%.

8. 8. The MEA of any one of claims 1 to 7, wherein the ruthenium is present in the Pt-Ru catalyst in an amount of 90-10 wt%, 70-30 wt%, or 50 wt%.

9. A method for producing an MEA according to any one of claims 1 to 8, said method comprising: coating a second side of the PEM with an anode catalyst; applying a Pt—Ru catalyst to the second side of the PEM such that the Pt—Ru catalyst is in electrical contact with the anode catalyst and in ionic contact with the PEM.

10. anchoring the anode channel over the anode catalyst such that the anode channel is in fluid communication with the anode catalyst; anchoring the cathode channel on the cathode catalyst such that the cathode channel is in fluid communication with the cathode catalyst; applying the Pt—Ru catalyst to the second side between the PEM and the anode channel; 10. The method of claim 9, further comprising:

11. The applying step includes: (i) dispersing the Pt—Ru catalyst in a flowable anode catalyst to form a mixture and coating the mixture onto the PEM; and / or (ii) forming a layer of the Pt—Ru catalyst on the PEM before coating the second side of the PEM with the anode catalyst.

11. The method of claim 9 or claim 10, comprising:

12. The catalyst is 0.005 to 0.5 mg / cm ２ , preferably 0.02 to 0.1 mg / cm ２ The method according to any one of claims 9 to 11, wherein the amount of

13. The method of any one of claims 9 to 12, wherein the platinum is present in the Pt-Ru catalyst in an amount of 10 to 90 wt%, 30 to 70 wt%, or 50 wt%.

14. 14. The method of any one of claims 9 to 13, wherein the ruthenium is present in the Pt-Ru catalyst in an amount of 90 to 10 wt%, 70 to 30 wt%, or 50 wt%.

15. Use of an MEA according to any one of claims 1 to 8 for producing hydrogen.

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