membrane

Abstract

An electrolyte membrane is provided that includes a recombination catalyst layer. The membrane is a single coherent polymer film having a thickness of 100 μm or less and including multiple ion-conducting polymer layers. The recombination catalyst layer includes unsupported recombination catalyst particles dispersed in an ion-conducting polymer, and the layer has a thickness in the range of 5 to 30 μm, inclusive. A catalyst-coated membrane (CCM) incorporating the electrolyte membrane is also provided, along with a method for manufacturing the electrolyte membrane.

Description

[Technical Field]

[0001] The present invention relates to electrolyte membranes and their use in electrochemical devices such as water electrolysis devices, including catalyst-coated membranes (CCMs) incorporating such membranes and methods for their manufacture. [Background technology]

[0002] Electrolysis of water to produce high-purity hydrogen and oxygen can be carried out in both alkaline and acidic electrolyte systems. Electrolyzers that use solid proton-conducting polymer electrolyte membranes or proton exchange membranes (PEMs) are known as proton exchange membrane water electrolyzers (PEMWEs). Electrolyzers that utilize solid anion-conducting polymer electrolyte membranes or anion exchange membranes (AEMs) are known as anion exchange membrane water electrolyzers (AEMWEs).

[0003] Catalyst-coated membranes (CCMs) can be used in water electrolysis stacks. CCMs include an electrolyte membrane, such as a PEM or AEM, with at least one of an anode catalyst layer and a cathode catalyst layer coated on the membrane surface. Typically, for PEMWEs, the cathode catalyst material includes platinum. Anode catalysts for PEMWEs typically include iridium or iridium oxide (IrOx) materials, or oxides containing both iridium and ruthenium.

[0004] To form a water electrolysis device, additional layers are added to either side of the CCM to create an assembly sometimes called a membrane electrode assembly (MEA). These additional layers can include a porous transport layer (PTL) on the anode side of the CCM and a gas diffusion layer (GDL) on the cathode side. These layers may or may not be directly attached to the CCM. Other components may include bipolar plates and current collector plates. A stack of such assemblies constitutes the electrolysis device system, including the power and control systems.

[0005] Electrolyte membranes such as PEMs and AEMs are also used in fuel cells. In a proton exchange membrane fuel cell (PEMFC), the membrane is proton-conducting, and protons generated at the anode are transported through the membrane to the cathode, where they combine with oxygen to form water.

[0006] It is desirable to reduce the thickness of membranes used in electrochemical devices such as water electrolyzers to minimize electrical and ionic resistance, however, it is also important to minimize any hydrogen crossover through the membrane to avoid mixing of hydrogen and oxygen and associated safety concerns.

[0007] For water electrolysis devices, it is beneficial to maintain low levels of hydrogen crossover even when the pressure difference across the membrane is high. The use of high pressure during electrolysis operation is advantageous because it reduces the degree of compression required of the produced hydrogen, reducing operating costs. This has led to the use of membranes with thicknesses greater than 125 μm, typically approaching 200 μm or even thicker. Examples of membranes currently in use include Nafion™ N115 (125 μm thick) or Nafion™ N117 (175 μm thick).

[0008] It is also important that the membrane be stable during long-term electrochemical operation to minimize maintenance and replacement of expensive components.

[0009] It is known to coat membrane components with a catalyst layer suitable for catalyzing the recombination reaction of molecular oxygen and hydrogen. For example, WO 2018 / 115821 (Johnson Matthey Fuel Cells Ltd) describes that a Pt / C supported catalyst can be coated on one surface of a membrane, and this membrane can be laminated to other membrane layers to form a CCM component for a PEM water electrolysis device.

[0010] It is also known to produce proton exchange membranes containing supported recombination catalysts. For example, WO 2020 / 148545 (Johnson Matthey Fuel Cells Ltd) describes that catalysts containing platinum nanoparticles on a graphene support can be incorporated into membranes.

[0011] There remains a need for further improvements and developments in membranes for electrochemical applications, such as water electrolysis, that allow efficient operation at high pressure differentials across the membrane. Summary of the Invention

[0012] The present inventors have surprisingly found that electrolyte membranes having thicknesses of 100 μm or less can be produced that exhibit an excellent balance between low hydrogen crossover and high ionic conductivity. Such membranes can be produced by dispersing unsupported recombination catalyst particles in membrane layers of controlled thickness and forming the membrane as a single coherent membrane without lamination interfaces. Such membranes allow the incorporation of the recombination catalyst while maintaining high ionic conductivity.

[0013] Accordingly, in a first aspect of the present invention, there is provided an electrolyte membrane comprising a recombination catalyst layer, such as a proton exchange membrane, wherein the membrane has a thickness of 100 μm or less, and the recombination catalyst layer satisfies the following requirements: (i) the layer comprises particles of an unsupported recombination catalyst dispersed in an ion-conducting polymer; (ii) the layer has a thickness in the range of 5 to 30 μm (inclusive); An electrolyte membrane is provided, wherein the electrolyte membrane is a single coherent polymer film comprising multiple ion-conducting polymer layers.

[0014] Such membranes are particularly suitable for use in water electrolysis devices, for example, providing the membrane as a single, non-laminated component rather than two or more membrane components laminated together provides additional stability benefits and large-scale manufacturing process efficiencies.

[0015] The membrane of the first aspect is particularly useful as a component of a catalyst-coated membrane (CCM). Such a CCM has been found to provide an excellent balance between membrane resistance during operation and low hydrogen crossover. Thus, in a second aspect of the present invention, there is provided a CCM for an electrochemical device comprising a membrane according to the first aspect.

[0016] Preferably, the CCM is for use in a water electrolysis device, such as a PEM water electrolysis device. In such cases, the CCM comprises a cathode catalyst layer for catalyzing the hydrogen evolution reaction and / or an anode catalyst layer for catalyzing the oxygen evolution reaction. Typically, the cathode catalyst layer comprises platinum and / or the anode catalyst layer comprises iridium.

[0017] The CCM may also be for use in a fuel cell, such as a PEM fuel cell, in which case the CCM includes a cathode catalyst layer for catalyzing the oxygen reduction reaction and / or an anode catalyst layer for catalyzing the hydrogen oxidation reaction.

[0018] In a third aspect of the present invention there is provided a water electrolyser or fuel cell comprising a membrane according to the first aspect or a catalyst coated membrane according to the second aspect.

[0019] The present inventors have also found that, advantageously, an electrolyte membrane comprising a recombination catalyst layer as described herein can be prepared by preparing an ink, preferably with controlled recombination catalyst particle size distribution, and then using such ink to prepare a recombination catalyst layer. Accordingly, in a fourth aspect of the present invention, there is provided a method of producing an electrolyte membrane according to the first aspect, comprising the steps of: (i) forming an ink comprising particles of an unsupported recombination catalyst and an ion-conducting polymer; (ii) fabricating a recombination catalyst layer from the ink. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows a schematic diagram of an exemplary configuration of an electrolyte membrane of the present invention. [Figure 2] 1 shows a schematic diagram of an exemplary configuration of a catalyst coated membrane of the present invention. [Figure 3] 1 shows a scanning electron microscopy (SEM) image of a film formed according to Example 1. [Figure 4] 1 shows the results of hydrogen crossover testing of the membranes produced in the examples. [Figure 5] 1 shows the results of electrical testing of 80 μm films produced in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] Preferred and / or optional features of the invention will now be described. Any aspect of the invention may be combined with any other aspect of the invention unless the context requires otherwise. Any preferred and / or optional feature of any aspect may be combined with any aspect of the invention, either singly or in any combination, unless the context requires otherwise.

[0022] The present invention provides an electrolyte membrane. It may be preferred that the membrane is a proton exchange membrane (PEM), such as a PEM for a water electrolyzer. However, those skilled in the art will understand that the recombination catalyst layer described herein has utility in other types of electrolyte membranes, such as proton exchange membranes for fuel cells, and anion exchange membranes for water electrolyzers, fuel cells, or other applications.

[0023] The membrane has a thickness of 100 μm or less. It may be preferred that the membrane has a thickness of 95 μm, 90 μm, or 85 μm or less. It may be preferred that the membrane has a thickness of at least 10 μm, for example, at least 15 μm, at least 20 μm, at least 25 μm, at least 30 μm, or at least 40 μm. It may be more preferred that the membrane has a thickness in the range (inclusive) of 10 to 100 μm, for example, 15 to 100 μm, 20 to 100 μm, 30 to 100 μm, 30 to 90 μm, or 40 to 90 μm.

[0024] Film thickness (and film layer thickness) can be measured by scanning electron microscopy (SEM). SEM analysis is performed on a cross-section of the film, measuring the film and / or layer thickness at multiple (e.g., 10) points. The thickness value is then determined by calculating the arithmetic mean of the measurements.

[0025] The membrane includes a recombination catalyst layer. By recombination catalyst is meant a catalyst that catalyzes the reaction between hydrogen and oxygen to form water. Thus, the recombination catalyst used in the recombination catalyst layer of the present invention may be any catalyst that can catalyze the reaction between hydrogen and oxygen to form water, thereby reducing or preventing the crossover of either hydrogen or oxygen, or both, through the membrane. Those skilled in the art will understand that the membrane may include more than one recombination catalyst layer, for example, two or more recombination catalyst layers. It may be preferable for the membrane to have a single recombination catalyst layer.

[0026] Suitably, the recombination catalyst is selected from one or more of platinum, palladium, and alloys or mixed oxides thereof. Preferably, the recombination catalyst is platinum or a platinum alloy, for example, platinum alloyed with one or more other platinum group metals (i.e., the group of elements including platinum, palladium, iridium, rhodium, ruthenium, and osmium), or platinum alloyed with cobalt. It may be particularly preferred that the unsupported recombination catalyst particles consist of platinum.

[0027] The recombination catalyst is unsupported. The term "unsupported" will be readily understood by those skilled in the art. For example, it will be understood that the catalyst particles are not bound or immobilized to a catalyst support, such as a carbon support, by physical or chemical bonds, for example, by ionic or covalent bonds, or by non-specific interactions such as der Waals forces. The use of an unsupported recombination catalyst has been found to facilitate ink processing prior to film formation, increase film stability during electrochemical operation, and avoid degradation pathways via corrosion of the catalyst support.

[0028] The recombination catalyst layer is a membrane layer containing particles of unsupported recombination catalyst dispersed in an ion-conducting polymer.

[0029] When the membrane is for use in a PEM electrochemical device, the ion-conducting polymer is preferably a proton-conducting polymer, particularly a partially or fully fluorinated sulfonic acid polymer. Examples of suitable proton-conducting polymers include perfluorosulfonic acid (PFSA) polymers, such as perfluorosulfonic acid polymers available from 3M Corporation, or Aquivion (RTM) ion-conducting polymers available from Solvay. It may be preferred that the ion-conducting polymer is a PFSA polymer and has an equivalent weight (EW) of greater than 750 EW, greater than 760 EW, greater than 770 EW, or greater than 790 EW. For example, it may be preferred that the ion-conducting polymer is a PFSA polymer having an equivalent weight in the range of 750 to 1200 EW, inclusive, such as 770 to 1000 EW or 800 to 900 EW, inclusive. It may be preferred that the equivalent weight of ion-conducting polymer in the recombination catalyst layer is greater than the equivalent weight of ion-conducting polymer in any other layer of the membrane.

[0030] Dispersed in the ion-conducting polymer, as used herein, means that the unsupported recombination catalyst particles are distributed throughout the recombination catalyst layer, i.e., the particles are not located in discrete layers or regions of the recombination catalyst layer.

[0031] The particles of the unsupported recombination catalyst preferably have a particle size distribution such that d90 is 3.0 μm or less. The use of particles with d90 of 3.0 μm or less provides improved mechanical stability in thin film layers (such as layers with a thickness of less than 30 μm), providing benefits related to ink processability and the use of the ink in coating equipment. The term d90 used in relation to particle size distribution in a film refers to the number distribution of particle sizes (the value of the particle size at 90% in the cumulative number distribution, i.e., 90% of all particles in a sample have a diameter smaller than this value). The d90 of particles in a film can be determined by scanning electron microscopy (SEM), for example, by analyzing a cross-section of the film by SEM, measuring the diameter of a population of particles (e.g., 100 particles) from the obtained image by image analysis, and then calculating d90.

[0032] It may be preferred that the d90 is 2.8 μm, 2.6 μm, 2.5 μm, 2.4 μm, 2.3 μm, 2.2 μm, 2.1 μm, or 2.0 μm or less. It may be preferred that the unsupported recombination catalyst particles have a particle size distribution such that the d90 is 1.0 μm, 1.5 μm, 1.7 μm, or 1.9 μm or more. It may be more preferred that the unsupported recombination catalyst particles have a particle size distribution such that the d90 is 1.0 to 3.0 μm or 1.5 to 3.0 μm, for example, 1.5 to 2.8 μm or 1.5 to 2.6 μm, inclusive.

[0033] Typically, unsupported recombination catalyst particles have an average particle size of 0.1 μm or greater. The average particle size can be determined by scanning electron microscopy (SEM), for example, by analyzing a cross section of the membrane with SEM, measuring the diameter of a population of observable particles (e.g., 100 particles) from the resulting image by image analysis, and then calculating the average particle size. The use of particles larger than 0.1 μm offers advantages for efficient ink preparation, and their use has been shown to significantly reduce hydrogen crossover.

[0034] It may be preferred that the average particle size is 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or 0.9 μm or greater. It may be preferred that the unsupported recombination catalyst particles have an average particle size of 2.0 μm, 1.8 μm, 1.6 μm, 1.5 μm, 1.4 μm, 1.3 μm, or 1.2 μm or less. It may be preferred that the unsupported recombination catalyst particles have an average particle size in the range of 0.2 to 2.0 μm, 0.5 to 2.0 μm, e.g., 0.7 to 1.8 μm, or 0.8 to 1.5 μm (inclusive).

[0035] Preferably, the electrolyte membrane has a density of 5 to 50 μg / cm -2 , 5-40μg / cm -2 , 5-30μg / cm -2 , 5-20μg / cm -2 range (including boundary values), e.g., 8-15 μg / cm -2 The membrane has a recombination catalyst loading (e.g., platinum loading) in the range (inclusive) of 0.01 to 0.01. This catalyst loading range has been found to provide an appropriate balance between reducing the level of hydrogen crossover during use and the costs associated with including a catalyst in the membrane. Catalyst loading can be determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0036] The recombination catalyst layer has a thickness in the range of 5 to 30 μm, inclusive. Dispersion of unsupported recombination catalyst particles in a membrane layer of at least 5 μm provides the advantage of improved membrane stability compared to the use of a thinner catalyst layer, for example, applied to the membrane surface. The use of a recombination catalyst layer with a thickness greater than 30 μm is not necessary to substantially reduce hydrogen crossover and may result in manufacturing difficulties, especially when forming non-laminated membrane structures. The thickness of the recombination catalyst layer can be determined by SEM analysis of the membrane cross section. It may be preferable for the recombination catalyst layer to have a thickness in the range of 5 to 20 μm, e.g., 7 to 15 μm, inclusive. Such a thickness provides an appropriate balance between reduction of hydrogen crossover by the formed membrane and manufacturing efficiency.

[0037] The membrane is formed by depositing multiple layers of ion-conducting polymers on top of each other via a liquid deposition process such as printing, spraying, or coating by a method that does not require a lamination step to form the membrane.

[0038] The membrane is a single coherent polymer film comprising multiple ion-conducting polymer layers. As used herein, the term "coherent" means that the membrane does not include internal laminate interfaces.

[0039] Lamination of ion-conducting membranes involves pressing and / or bonding at least two solid, ion-conducting membranes together, optionally coated with a catalyst layer. A lamination interface is formed between the two membranes, where the solid surfaces of the individual membranes are pressed and / or bonded together. The lamination interface contains physical defects. Furthermore, the structural and / or chemical properties of the lamination interface also differ from those of the bulk polymer material. This is because, when a solid membrane is formed, the outer surface of the solid membrane has surface characteristics that differ from those of the bulk material. For example, a hydrophobic skin forms on the surface of the membrane at the air interface. Raman spectroscopy can detect this difference. Thus, when two solid membranes are pressed together, the lamination interface formed by the two solid surfaces has a distinctive chemical and / or structural morphology compared to the bulk of the ion-conducting polymer material. Therefore, microscopy and spectroscopy can distinguish a lamination interface between layers of ion-conducting polymers from an interface formed by a liquid deposition process, such as printing, spraying, or coating layers to build a multilayer structure. That is, non-laminated interfaces are structurally and / or chemically distinct from laminated interfaces and are not merely a feature of the fabrication process. Furthermore, non-laminated interfaces can be identified as non-laminated in a film without prior knowledge of the fabrication process. Examples of analytical techniques for detecting laminated interfaces include cross-sectional SEM. Changes in crystallinity at interfaces can be detected using cross-sectional TEM. Other techniques for detecting laminated interfaces include 13C / 1H / 19F solid-state NMR, neutron diffraction, and / or a combination of two or more of the aforementioned techniques.

[0040] Due to physical defects and / or chemical variations at the stacked interfaces between ion-conducting polymer films, such interfaces may increase the resistance of the multilayer ion-conducting membrane. Therefore, it has been found advantageous to fabricate multilayer ion-conducting membranes by building up a multilayer membrane structure by depositing layers of ion-conducting polymers dispersed in a liquid solvent, rather than through stacking of individual solid layers / films of ion-conducting polymers.

[0041] Preferably, the membrane comprises a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). In some cases, it may be preferred that the recombination catalyst layer does not comprise a reinforcing polymer.

[0042] The reinforcing material may include a porous reinforcing polymer sheet impregnated with an ion-conducting polymer, the reinforcing material optionally being expanded polytetrafluoroethylene (ePTFE). Because typical reinforcing polymer materials are not conductive to ions or are not sufficiently conductive to ions, the reinforcing layer is formed using a porous reinforcing polymer impregnated with an ion-conducting polymer through the pores of the material to provide an ion-conducting path from one side of the layer to the other side of the layer.

[0043] Preferably, the membrane includes a radical reducing additive (e.g., a peroxide radical reducing additive such as ceria). Note that peroxides can decompose to form a range of radicals (O, OH, OOH), and the radical reducing additive can reduce the amount of one, more, or all of these radicals. The radical reducing additive can be dispersed within the recombination catalyst layer.

[0044] Typically, the membrane is configured such that a recombination catalyst layer (1) is disposed between a first ion-conducting polymer layer (2) and a second ion-conducting polymer layer (3), as shown in Figure 1. In such a configuration, the second surface (4) of the first ion-conducting polymer layer (2) and the second surface (5) of the second ion-conducting polymer layer (3) each face inward toward the recombination catalyst layer (1). The first surface (6) of the first ion-conducting polymer layer (2) and the first surface (7) of the second ion-conducting polymer layer (3) are the outer surfaces of the membrane, i.e., they face the anode and cathode when incorporated into, for example, a water electrolysis device.

[0045] Preferably, the membrane comprises a recombination catalyst layer disposed between a first ion-conducting polymer layer and a second ion-conducting polymer layer. Those skilled in the art will appreciate that the first ion-conducting polymer layer and the second ion-conducting polymer layer may be formed from one or more sublayers that may be of the same or different composition.

[0046] When the membrane is for use in a PEM electrochemical device, the ion-conducting polymers present in the first and second ion-conducting polymer layers are preferably proton-conducting polymers, particularly partially or fully fluorinated sulfonic acid polymers. Examples of suitable proton-conducting polymers include perfluorosulfonic acid ionomers, such as those available from 3M Corporation, or Aquivion (RTM) ion-conducting polymers available from Solvay. It may be preferred that the ion-conducting polymer in the first and / or second ion-conducting layers be the same as the ion-conducting polymer in the recombination catalyst layer. Alternatively, it may be preferred that the ion-conducting polymer in the first and / or second ion-conducting layers be different from the ion-conducting polymer in the recombination catalyst layer.

[0047] Typically, a reinforcing polymer and / or a radical reducing agent (eg, a peroxide radical reducing additive such as ceria) is present in the first and / or second ion-conducting polymer layers.

[0048] It may be preferable for the thickness of the first ion-conducting polymer layer to be thinner than the thickness of the second ion-conducting polymer layer. This asymmetry may allow the recombination catalyst layer to be located closer to the anode than to the cathode in a water electrolysis device configuration, which may be beneficial in reducing hydrogen crossover.

[0049] It may be preferred that the first ion-conducting polymer layer have a thickness in the range of 5 to 30 μm, inclusive, for example, 5 to 20 μm, or 5 to 15 μm, or 7 to 15 μm, inclusive. The inventors believe that such a thickness for the first ion-conducting polymer layer provides an appropriate distance between the anode layer and the recombination catalyst in a CCM formed for a water electrolysis device, significantly reducing hydrogen crossover.

[0050] It may be preferred that the second ion-conducting polymer layer has a thickness in the range of 10 to 90 μm inclusive, for example in the range of 20 to 70 μm, 40 to 70 μm, or 25 to 45 μm inclusive.

[0051] The thickness of the ion-conducting polymer layer can be adjusted, for example, by varying the number of deposition passes of the ion-conducting polymer during the fabrication of the membrane or by varying the pump speed during the deposition of the ion-conducting polymer.

[0052] The membrane may preferably comprise or consist of: (i) a first ion-conducting layer having a thickness in the range of 5 to 15 μm (inclusive); (ii) a second ion-conducting layer having a thickness in the range of 25 to 45 μm (inclusive); and (iii) a recombination catalyst layer having a thickness in the range of 5 to 15 μm (inclusive) and disposed between the first and second ion-conducting layers. In such a configuration, the second ion-conducting layer preferably comprises a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). Such a membrane structure has been found to provide a particularly suitable balance between membrane resistance and hydrogen crossover levels.

[0053] Preferably, the membrane comprises or consists of: (i) a first ion-conducting layer having a thickness in the range of 5 to 15 μm (inclusive); (ii) a second ion-conducting layer having a thickness in the range of 40 to 70 μm (inclusive); and (iii) a recombination catalyst layer having a thickness in the range of 5 to 15 μm (inclusive) and disposed between the first and second ion-conducting layers. In such a configuration, the second ion-conducting layer preferably comprises a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). It may further be preferred that the second ion-conducting layer comprises two regions of a reinforcing polymer, such as two sublayers comprising a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). Such a membrane structure allows operation at particularly high gas pressure differentials across the membrane while maintaining low hydrogen crossover and low membrane resistance.

[0054] The membranes described herein are suitable for use as part of a catalyst-coated membrane (CCM), which has an anode catalyst layer and / or a cathode catalyst layer applied to the surface of the membrane.

[0055] In the case of a CCM for a water electrolysis system, a cathode catalyst layer may be applied to the surface of the membrane, containing a catalyst for catalyzing the hydrogen evolution reaction. It may be preferable for the cathode catalyst layer to contain platinum, e.g., a platinum-on-carbon catalyst. The catalyst material may be formulated into an ink, printed ex-situ on a PTFE sheet, and transferred onto the membrane by hot pressing. Alternatively, the ink may be coated directly onto the membrane.

[0056] The cathode catalyst layer contains platinum, and the platinum loading provided by the platinum material (such as platinum-supported carbon material) is 1 mg. Pt cm -2It may be preferable for the platinum loading in the cathode layer to be less than 0.01 mg. Surprisingly, it has been found that when using platinum-on-carbon catalyst materials, decreasing the platinum loading actually improves performance in terms of current density. That is, decreasing the platinum loading using platinum-on-carbon catalyst materials surprisingly increases the current density for a given potential. That said, there is also a lower limit to the amount of platinum that must be provided. Therefore, the platinum loading in the cathode layer is preferably less than 0.01 mg. Pt cm -2 , 0.04 mg Pt cm -2 , or 0.06 mg Pt cm -2 Exceeds.

[0057] The cathode catalyst layer may comprise a platinum-on-carbon catalyst material that is 20-60% platinum by weight, optionally 40-60% platinum by weight. The platinum may be advantageously provided as nanoparticles on the carbon support material. The platinum nanoparticles may have a crystallite size of at least 1 nm, 2 nm, or 3 nm; or no more than 15 nm, no more than 10 nm, or no more than 6 nm; or within a range defined by any combination of the aforementioned lower and upper limits. The crystallite size may be measured by XRD and fitted using Rietveld analysis. X-ray diffraction data are collected on a Bruker AXS D8 using Cu Kα radiation (λ = 1.5406 and 1.54439 Å). The crystallite size is calculated from the Rietveld refinement using the LVol-IB method.

[0058] The cathode catalyst layer may include a platinum-on-carbon catalyst material in which the carbon support material is a partially graphitized carbon material (e.g., heat-treated carbon black). Graphite materials are more corrosion-resistant. However, graphite support materials have a low surface area. Therefore, there is a compromise between the requirements for a large surface area and high corrosion resistance. Partially graphitized materials have been found to be a good compromise between the surface area and corrosion resistance requirements for the carbon support in this water electrolysis application.

[0059] Typically, the cathode catalyst layer contains both a catalyst and an ion-conducting polymer. The ion-conducting polymer in the cathode catalyst layer can be an ionomer, such as a perfluorosulfonic acid (PFSA) polymer, having an equivalent weight of 880 EW, 850 EW, or 830 EW or less; 750 EW or more, 770 EW or more, or 790 EW or more; or within a range defined by any combination of the aforementioned upper and lower limits. The side chains of the cathode layer ion-conducting polymer typically each contain a sulfonate group. The side chains of the cathode layer ion-conducting polymer have the structure: -CF2-CF2-CF2-CF2-SO3 H An example of such an ionomer is 800EW 3M C4 side chain. The ion-conducting polymer of the cathode layer may be the same or similar to that used in the membrane.

[0060] The cathode catalyst layer may have an ion-conducting polymer / carbon weight ratio in the range of 0.6 to 1.0, inclusive (note that this is the weight ratio of ion-conducting polymer to carbon; platinum is not considered in this calculation). Additionally, the cathode catalyst layer may have a thickness in any range, including 1 to 15, 4 to 15, or 8 to 15 μm.

[0061] Examples of such cathode layers include the following features: -Nominal Pt load - 0.4mg Ptcm -2 -Ion Conductive Polymer-Ionomer 800EW 3M C4 Side Chain -Ion-conductive polymer / carbon weight ratio: 0.8 -Thickness - Approximately 10 to 11 μm -The catalyst is 50 wt% Pt supported on carbon - Carbon is a partially graphitized carbon support material

[0062] In the case of a CCM for a water electrolysis device, an anode catalyst layer may be applied to the surface of the membrane containing a catalyst for catalyzing the oxygen evolution reaction. If the CCM is for a PEMWE, it may be preferred that the anode catalyst layer comprises iridium, e.g., iridium oxide, or a mixed oxide of iridium and another metal element.

[0063] The anode material can be formulated into an ink, preferably an ion-conducting polymer, printed ex-situ onto a PTFE sheet and transferred onto the membrane by hot pressing. Alternatively, the ink can be coated directly onto the membrane.

[0064] The anode catalyst layer typically contains both a catalyst and an ion-conducting polymer. Advantageously, the ion-conducting polymer of the anode catalyst layer differs from the ion-conducting polymer in the membrane in that it has one or more of the following characteristics: a higher equivalent weight than the membrane ion-conducting polymer; longer side chains than the membrane ion-conducting polymer; and / or different chemical groups in the side chains than the membrane ion-conducting polymer. In contrast, the ion-conducting polymer used in the cathode catalyst layer may typically be the same as or similar to that used in the ionomer membrane.

[0065] The ion-conducting polymer in the anode catalyst layer preferably has an equivalent weight of 900 EW or more, 950 EW or more, 1000 EW or more, or 1050 EW or more and 1300 EW or less, 1200 EW or less, or 1150 EW or less, or within a range defined by any combination of the aforementioned lower and upper limits. The side chains of the ion-conducting polymer typically each contain a sulfonate group. Optionally, the side chains of the ion-conducting polymer contain an ether group in addition to an ether linkage to the backbone. Further, optionally, the side chains of the ion-conducting polymer contain CF groups. The side chains of the ion-conducting polymer may have the structure: -CF2-CF(CF3)-O-CF2-CF2-SO3H. An example of such an ionomer is Nafion D-2021CS. Nafion D-2021CS is a high equivalent weight ionomer with long side chains having sulfonate end groups. In the presence of water, these sulfonic acid groups hydrate, solvate, and dissociate into protons, allowing proton exchange from the anode to the cathode. In contrast, the ion-conducting polymer in the membrane can be, for example, 3M 800, 3M 825, or Asahi 800 ionomer. These ion-conducting polymers have lower equivalent weights and shorter side chains.

[0066] The anode catalyst layer may contain 5 to 20 wt %, for example 8 to 15 wt %, of the ion-conducting polymer. Suitably, the amount of catalyst material in the anode catalyst layer may be 80 to 95 wt %, optionally 85 to 92 wt %. The iridium loading of the anode catalyst layer is preferably 3 mg Ir / cm. 2 and optionally between 0.05 and 3 mg Ir / cm 2 The iridium-containing catalyst material may be an iridium oxide catalyst material, and the anode catalyst layer may have a thickness of 6 to 15 μm.

[0067] Typically, a CCM includes a membrane comprising a first ion-conducting polymer layer and a second ion-conducting polymer layer, with a recombination catalyst layer disposed between the first and second ion-conducting polymer layers, as described above. The CCM is preferably configured so that the recombination catalyst layer is closer to the anode catalyst layer than to the cathode catalyst layer. It may further be preferable for the second ion-conducting polymer layer to be thicker than the first ion-conducting polymer layer. Such a configuration has been proposed to be advantageous in terms of reducing hydrogen crossover.

[0068] Preferably, the CCM is configured such that, as shown in Figure 2, the second surface (4) of the first ion-conducting polymer layer (2) and the second surface (5) of the second ion-conducting polymer layer (3) each face inward toward the recombination catalyst layer (1). If present, the anode catalyst layer (8) is provided on the first surface (6) of the first ion-conducting polymer layer (2). If present, the cathode catalyst layer (9) is provided on the first surface (6) of the second ion-conducting polymer layer (3).

[0069] The catalyst-coated membrane may comprise or consist of (i) a first ion-conducting layer having a thickness in the range of 5 to 15 μm (inclusive), (ii) a second ion-conducting layer having a thickness in the range of 25 to 45 μm (inclusive), and (iii) a recombination catalyst layer having a thickness in the range of 5 to 15 μm (inclusive) and disposed between the first and second ion-conducting layers, wherein the second surfaces of the first and second ion-conducting polymer layers face inward toward the recombination catalyst layer, and the anode catalyst layer is disposed on the first surface of the first ion-conducting layer and / or the cathode catalyst layer is disposed on the first surface of the second ion-conducting layer. In such a configuration, the second ion-conducting layer preferably comprises a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI).

[0070] The catalyst-coated membrane may comprise or consist of (i) a first ion-conducting layer having a thickness in the range of 5 to 15 μm (inclusive), (ii) a second ion-conducting layer having a thickness in the range of 40 to 70 μm (inclusive), and (iii) a recombination catalyst layer having a thickness in the range of 5 to 15 μm (inclusive) and disposed between the first and second ion-conducting layers, wherein the second surfaces of the first and second ion-conducting polymer layers face inward toward the recombination catalyst layer, and the anode catalyst layer is disposed on the first surface of the first ion-conducting layer and / or the cathode catalyst layer is disposed on the first surface of the second ion-conducting layer. In such a configuration, the second ion-conducting layer preferably comprises a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI). It may further be preferred that the second ion-conducting layer comprises two regions of a reinforcing polymer, such as two sub-layers comprising a reinforcing polymer such as expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI).

[0071] Also, there is provided a method for producing the electrolyte membrane described herein, comprising the steps of: (i) forming an ink comprising particles of an unsupported recombination catalyst and an ion-conducting polymer; (ii) fabricating a recombination catalyst layer from the ink.

[0072] When the unsupported recombination catalyst particles are platinum particles, it is preferred that the platinum particles be provided as platinum black, which can be efficiently processed to provide inks suitable for use in the methods described herein and has been found to exhibit reduced agglomeration during ink formation than other platinum sources, such as platinum on carbon.

[0073] Preferably, the unsupported recombination catalyst particles in the ink have a d90 of less than 3.0 μm. The particle size distribution can be determined by using laser diffraction techniques. For example, d90 can be determined by diluting the ink with 80:20 (v / v) ethanol:water and analyzing the particle size distribution by laser diffraction, for example using a Malvern Mastersizer 3000. The term d90 for particles in an ink refers to the volumetric particle size (the value of the particle size at 90% in the cumulative volume distribution, i.e., 90% by volume of the particles in the sample have a diameter smaller than this value).

[0074] The desired particle size distribution may be suitably achieved by processing the ink using high shear techniques, such as microfluidization. It may be preferred that forming the ink in step (i) comprises passing a dispersion of a platinum source, such as platinum black, and an ion-conducting polymer through a microfluidizer.

[0075] The ink typically comprises an ion-conducting polymer dispersed in a solvent. The solvent may be a mixture of an organic solvent and water. For example, the solvent may be a mixture of an alcohol (e.g., ethanol or propanol) and water. The volume ratio of organic solvent, such as ethanol, to water may be at least 60:40, 70:30, or 75:25; 95:5; 90:10, or 85:15 or less; or within a range defined by any combination of the foregoing lower and upper limits. The solvent is formulated to achieve desired dispersion, coating, and drying characteristics.

[0076] The ion-conducting polymer may be provided in the ink in a weight percent of at least 7%, 10%, 14%, or 16% by weight, or no more than 22%, 20%, or 18% by weight, based on the total weight of the recombination catalyst and ion-conducting polymer; or within a range defined by any combination of the foregoing lower and upper limits. The amount of ion-conducting polymer present is selected to achieve desired dispersion, coating, and drying characteristics.

[0077] The ink may also include a radical reducing additive (e.g., a peroxide radical reducing additive such as ceria). For example, the radical reducing additive may be provided in the dispersion in a weight percent of at least 0.15 wt %, 0.20 wt %, or 0.23 wt %, based on the weight of the ion-conducting polymer; or no more than 0.35 wt %, no more than 0.30 wt %, or no more than 0.28 wt %, or within a range defined by any combination of the foregoing lower and upper limits.

[0078] The method includes fabricating a recombination catalyst layer from an ink. The recombination catalyst layer is typically formed by casting or printing the ink onto a substrate to form a layer. The layer thus formed is typically allowed to dry, or at least partially dry, before depositing a further layer of ionomer thereon.

[0079] Typically, the substrate is a layer of an ion-conducting polymer layer, such as a first or second ion-conducting polymer layer. It may be preferred that step (ii) comprises fabricating the recombination catalyst layer from the ink by depositing the ink on the first ion-conducting polymer layer.

[0080] Further ion-conducting polymer layers may be deposited to form the membrane. It may be preferred that the method includes step (iii) of adding a second ion-conducting polymer layer such that the recombination catalyst layer is disposed between the first and second ion-conducting polymer layers.

[0081] The membrane may be formed by sequential printing of layers. As an example, the membrane may be formed as follows: In a first pass, an ion-conducting polymer layer is applied onto a backing layer. The first ion-conducting polymer layer is then dried. In a second pass, an ink containing a recombination catalyst is applied onto the first ion-conducting polymer layer. The recombination catalyst layer is then dried. This sequence of application and drying is continued to produce additional ion-conducting polymer sublayers during additional passes to form a second ion-conducting polymer layer. Reinforcement materials may be included in one or more of the coating passes.

[0082] The membrane structure described above can be coated with cathode and anode catalysts to form a catalyst-coated membrane (CCM) for a water electrolysis device. The specific type of catalyst for the cathode and anode can be varied. Furthermore, the deposition method can be varied. An example of a suitable cathode catalyst for a water electrolysis device is a platinum-on-carbon catalyst, optionally provided as a decal. For a CCM for a PEMWE, an iridium oxide-based catalyst can be used for the anode. The iridium oxide-based catalyst can be formulated into an ink containing an ion-conducting polymer, 1-propanol, and water, bar-coated onto a Teflon sheet, and dried to form a decal. The catalyst decal can be hot-pressed with the membrane to form a CCM.

[0083] The present invention will now be described with reference to the following examples, which are provided to aid in the understanding of the invention and are not intended to limit its scope. [Example]

[0084] Example 1 - Formation of Recombination Catalyst-Containing Ink A mixture of ion-conducting polymer (PFSA ionomer, 825EW, 3M Advanced Materials) and ethanol:water (80:20) was prepared. Platinum black catalyst (Johnson Matthey plc) was added to the mixture at a target amount of 8.8 wt% platinum black based on the total weight of platinum, ionomer, ethanol, and water.

[0085] This mixture was passed through a microfluidizer (Microfluidics M-110P) using a z-chamber at 30,000 psi until the observable viscosity of the ink was significantly reduced.

[0086] Analysis of the particle size distribution of the platinum particles in the ink using a Mastersizer 3000 showed that the d90 was approximately 0.9 μm and the d50 was approximately 0.17 μm.

[0087] Then, 1 cm 2 The concentrated ink was diluted again using a mixture of 3M ionomer PFSA 825EW and ethanol:water (80:20) to achieve approximately 10 micrograms of Pt per ink.

[0088] Example 2 - Formation of a 50 μm proton exchange membrane incorporating a recombination catalyst layer Slot die coating using a series of five printing / coating passes onto a Diacel substrate (PET with a release layer on one side) was used to prepare a 50 μm membrane incorporating a recombination catalyst layer using the recombination catalyst-containing ink produced according to Example 1 in the second pass.

[0089] All other layers were formed from an ink containing perfluorosulfonic acid (PFSA) ionomer (3M 800EW PFSA ionomer), ceria (approximately 0.3 wt. % based on the weight of the ionomer) in ethanol:water (80:20). A reinforcing polymer was added to the ink used in pass 3 by including expanded polytetrafluoroethylene (ePTFE) reinforcing material. The following table summarizes the materials and methods used to construct the membranes.

[0090] The five coating passes to fabricate a 50 μm membrane are as follows:

[0091] [Table 1]

[0092] The films were dried at temperatures between 100 and 160°C and then annealed at 160°C.

[0093] Example 3 - Formation of an 80 μm proton exchange membrane incorporating a single domain containing a recombination catalyst layer and an ePTFE reinforcement A membrane was produced according to Example 2 with three more coating passes to form an 80 μm proton exchange membrane.

[0094] Example 4 - Formation of an 80 μm proton exchange membrane incorporating two regions containing a recombination catalyst layer and an ePTFE reinforcement. A membrane was produced according to Example 1 using the following sequence of seven passes:

[0095] [Table 2]

[0096] Membrane analysis and characterization Inductively coupled plasma mass spectrometry (ICP-MS): The platinum loading in the 50 μm membrane prepared in Example 2 was determined to be 13 μg / cm by ICP-MS. 2 (Membrane 1cm 2The Pt mass per unit area was measured.

[0097] The platinum loading in the 80 μm membrane prepared in Example 3 was determined to be 13 μg / cm by ICP-MS. 2 was measured.

[0098] Scanning Electron Microscopy (SEM): A cross section of each fabricated membrane was embedded in resin, ground, polished, and carbon-coated for SEM. Samples were analyzed using a Zeiss Ultra 55 field emission electron microscope. The boundary between the recombination catalyst layer and another layer is identified by where the recombination catalyst dispersion ends.

[0099] Figure 3 shows an SEM image of a cross section of a 50 μm membrane, which shows the presence of platinum particles dispersed throughout the 50 μm membrane thickness and a recombination catalyst layer approximately 12 μm thick.

[0100] Analysis of the platinum particle size distribution from SEM images of 50 films shows that the d90 is about 2.5 μm and the d50 is about 1.2 μm.

[0101] Catalyst Coated Membrane (CCM) Testing CCMs were prepared using 50 and 80 μm proton exchange membranes containing the recombination catalyst prepared according to the methods of Examples 2 and 3, as well as equivalent comparative examples produced according to Examples 2 and 3, except that a platinum-free ionomer ink (i.e., no recombination catalyst) was used for pass 2. A Pt / C cathode catalyst layer (0.37 mg cm) was used. -2 Pt) and an IrOx anode catalyst layer (2 mg cm -2 CCMs were prepared using a 1000 sachets membrane (with an Ir loading of 1000 sachets). For CCMs incorporating a recombination catalyst, the anode layer was applied to the side of the membrane closest to the recombination catalyst layer.

[0102] Hydrogen Crossover The level of hydrogen crossover for each CCM was measured at different pressures using the following method. A water electrolysis cell incorporating the catalyst-coated membrane to be tested was prepared. The cell temperature was maintained at 80°C, and the anode and cathode pressures were set to 2 bar. Then, a current density of 2 A / cm was applied. 2 The cathode pressure was increased in steps from 2 bar to 6, 10, and 15 bar, with a minimum duration of 45 minutes for each step. The % H in oxygen at the anode gas outlet was measured by a Compact GC 4.0 Gas Chromatograph (GC) from Global Analysis Solutions.

[0103] Figure 4 shows the results of the CCM tests. These results demonstrate that the membranes produced according to Examples 2 and 3 exhibit significantly reduced hydrogen crossover, even at high transmembrane pressure differentials. The 80 μm proton exchange membrane formed according to Example 3 provides the best performance at high pressure differentials.

[0104] Electrical Performance The electrical performance of the CCM was tested by the following method. First, the CCM was conditioned via potentiostatic stabilization at 2 V and 80 °C for 18-24 hours. Polarization measurements were then performed. The anode and cathode pressures were kept equal at 2 bar. Measurements were performed at 80 °C and 3 A / cm. 2 Starting from 0.1A / cm 2 0.1A / cm² in increments of 3.0A / cm² 2 The upward measurement (low to high current) was used for further analysis.

[0105] Test results for the 80 μm proton exchange membrane are shown in Figure 5. The results indicate that including a recombination catalyst layer as described herein does not have a detrimental effect on the membrane's performance. The data show that the membrane provides a CCM with a particularly favorable balance of resistance and hydrogen crossover levels, allowing for high pressure operation.

[0106] Also, (30 μg / cm 2CCMs incorporating 50 micron membranes with and without a recombination catalyst-containing membrane layer (having a Pt loading of 0.3 A cm) were also prepared. -2 The through-plane resistance of the CCM was measured using electronic impedance spectroscopy (EIS) and found to be 64-75 μΩ / cm for the CCM without the recombination catalyst-containing membrane layer. 2 The value was 62 to 69 μΩ / cm for the CCM without the recombination catalyst-containing membrane layer. 2 These results demonstrate that the recombination catalyst can be advantageously incorporated into the membrane as described above without adversely affecting the resistance.

Claims

1. An electrolyte membrane comprising a recombination catalyst layer, wherein the membrane has a thickness of 100 μm or less, and the recombination catalyst layer satisfies the following requirements: (i) The layer comprises unsupported recombination catalyst particles dispersed in an ion-conducting polymer, (ii) The layer has a thickness in the range of 5 to 30 μm (including boundary values), The electrolyte membrane is a single adhesive polymer film comprising multiple ion-conducting polymer layers, and includes a recombination catalyst layer.

2. The electrolyte membrane according to claim 1, wherein the recombination catalyst is selected from one or more of platinum, palladium, and their alloys or mixed oxides.

3. The electrolyte membrane according to claim 1, wherein the particles of the unsupported recombination catalyst have a particle size distribution such that d90 is 3.0 μm or less.

4. The electrolyte membrane according to claim 1, wherein the unsupported recombination catalyst particles have an average particle size greater than 0.1 μm, for example, an average particle size in the range of 0.5 μm to 2.0 μm (including boundary values).

5. The electrolyte membrane according to claim 1, wherein the membrane has a thickness in the range of 5 to 100 μm (including boundary values), preferably in the range of 30 to 90 μm (including boundary values).

6. The electrolyte membrane according to claim 1, wherein the membrane comprises a reinforcing polymer such as stretched polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI).

7. The electrolyte membrane according to claim 1, comprising a first ion-conducting polymer layer and a second ion-conducting polymer layer, wherein the recombination catalyst layer is disposed between the first ion-conducting polymer layer and the second ion-conducting polymer layer.

8. The electrolyte membrane according to claim 7, wherein the membrane comprises a reinforcing polymer, and the reinforcing polymer is present in the first ion-conducting polymer layer and / or the second ion-conducting polymer layer.

9. The electrolyte membrane according to claim 7, wherein the first ion-conducting polymer layer has a thickness in the range of 5 μm to 30 μm (including boundary values), preferably in the range of 5 μm to 20 μm (including boundary values), or in the range of 5 μm to 15 μm (including boundary values).

10. The electrolyte membrane according to claim 6, wherein the second ion-conducting polymer layer has a thickness in the range of 10 μm to 90 μm, preferably in the range of 40 μm to 70 μm (including boundary values) or in the range of 25 to 45 μm (including boundary values).

11. The electrolyte membrane according to claim 7, wherein the second ion-conducting layer includes two regions of a reinforcing polymer.

12. The electrolyte membrane according to claim 1, wherein the recombination catalyst layer has a thickness in the range of 5 to 15 μm (including boundary values).

13. A catalyst coating film for an electrochemical device such as a water electrolysis apparatus, comprising the electrolyte membrane described in any one of claims 1 to 12.

14. The catalyst coating film according to claim 13, wherein the electrolyte film comprises a first ion-conducting polymer layer and a second ion-conducting polymer layer, the recombination catalyst layer is disposed between the first ion-conducting polymer layer and the second ion-conducting polymer layer, the anode catalyst layer is disposed on the first surface of the first ion-conducting polymer layer, and the second surface of the first ion-conducting polymer layer faces the direction of the recombination catalyst layer.

15. The catalyst coating film according to claim 14, wherein the thickness of the first ion-conducting layer is thinner than the thickness of the second ion-conducting layer.

16. The catalyst coating film according to claim 13, wherein the electrolyte film comprises a first ion-conducting polymer layer and a second ion-conducting polymer layer, the recombination catalyst layer is disposed between the first ion-conducting polymer layer and the second ion-conducting polymer layer, the cathode catalyst layer is disposed on the first surface of the second ion-conducting polymer layer, and the second surface of the second ion-conducting polymer layer faces the direction of the recombination catalyst layer.

17. The catalyst coating film according to claim 14, wherein the first ion-conducting polymer layer has a thickness in the range of 5 μm to 30 μm (including boundary values), preferably in the range of 5 μm to 20 μm (including boundary values).

18. The catalyst coating film according to claim 14, wherein the second ion-conducting polymer layer has a thickness in the range of 10 μm to 90 μm (including boundary values), preferably in the range of 40 μm to 70 μm (including boundary values).

19. A water electrolysis apparatus comprising the film described in claim 1 or the catalyst coating film described in claim 13.

20. A fuel cell comprising the film described in claim 1 or the catalyst coating film described in claim 13.

21. A method for producing an electrolyte membrane according to any one of claims 1 to 12, (i) A step of forming an ink comprising unsupported recombination catalyst particles and an ion-conducting polymer, (ii) A method comprising the step of preparing a recombination catalyst layer from the ink.

22. The method according to claim 21, wherein the ink is formed by passing a dispersion of platinum black and an ion-conducting polymer through a microfluidizer.

23. The method according to claim 21, wherein step (ii) comprises depositing the ink onto a first ion-conducting polymer layer.

24. The method according to claim 23, comprising the step (iii) of adding a second ion-conducting polymer layer such that the recombination catalyst layer is disposed between the first ion-conducting polymer layer and the second ion-conducting polymer layer.

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