Catalyst preparation

Abstract

The present invention provides a method of preparing a catalyst material, the catalyst material comprising a support material and an electrocatalyst dispersed on the support material; the method comprising the steps of: i) providing a support material; then ii) depositing a silicon oxide precursor on the support material; then iii) performing a heat treatment step to convert the silicon oxide precursor to silicon oxide; then iv) depositing the electrocatalyst or a precursor of the electrocatalyst on the support material; then v) removing at least some of the silicon oxide.

Description

Technical Field

[0001] This invention relates to a method for preparing a catalyst material, the method comprising the step of adding silicon oxide to a support material prior to electrocatalyst deposition. Background Technology

[0002] A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. Fuel (e.g., hydrogen, alcohol (such as methanol or ethanol), or formic acid) is supplied to the anode, and an oxidant (e.g., oxygen or air) is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and oxidant is converted into electrical energy and heat. Electrocatalysts are used to facilitate the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.

[0003] Fuel cells are typically classified according to the properties of the electrolyte used. The electrolyte is usually a solid polymer membrane that is electrically insulating but ionicly conductive. In a proton exchange membrane fuel cell (PEMFC), this ionicly conductive membrane is proton-conducting, and protons generated at the anode are transported across this membrane to the cathode, where they combine with oxygen to form water.

[0004] The main component of a PEMFC is the membrane electrode assembly, which consists of approximately five layers. The middle layer is a polymer ion-conducting membrane. An electrocatalyst layer, containing an electrocatalyst designed for a specific electrolytic reaction, is located on either side of the ion-conducting membrane. Finally, a gas diffusion layer is adjacent to each electrocatalyst layer. The gas diffusion layer must allow reactants to reach the electrocatalyst layer and must conduct the current generated by the electrochemical reaction. Therefore, the gas diffusion layer must be porous and conductive.

[0005] The electrocatalyst layer typically also contains proton-conducting materials, such as proton-conducting polymers, to facilitate the transfer of protons from the anode electrocatalyst to the ion-conducting membrane and / or from the ion-conducting membrane to the cathode electrocatalyst.

[0006] Conventionally, membrane electrode assemblies can be constructed using a variety of methods. Typically, these methods involve applying one or both electrocatalyst layers to an ion-conducting membrane to form a catalyst-coated ion-conducting membrane. Subsequently, a gas diffusion layer is applied to the electrocatalyst layers. Alternatively, an electrocatalyst layer is applied to a gas diffusion layer to form a gas diffusion electrode, which is then combined with the ion-conducting membrane. Membrane electrode assemblies can be prepared by a combination of these methods, for example, applying one electrocatalyst layer to an ion-conducting membrane to form a catalyst-coated ion-conducting membrane and applying another electrocatalyst layer as a gas diffusion electrode. The electrocatalyst layers are applied using an electrocatalyst ink that typically comprises an electrocatalyst material, an ion-conducting polymer, a solvent and / or a diluent, and any reagents desired to be included in the electrocatalyst layers.

[0007] Electrocatalyst layers typically contain electrocatalyst materials comprising metals or metal alloys suitable for fuel oxidation or oxygen reduction reactions, depending on whether the layer is intended for use as an anode or cathode. Electrocatalysts for fuel oxidation and oxygen reduction are typically based on platinum or platinum alloyed with one or more other metals. Platinum or platinum alloy electrocatalysts can be in the form of unsupported nanoscale particles (e.g., metallic black) or can be deposited as discrete nanoparticles with very high surface area onto a conductive support material (supported electrocatalyst), such as high surface area carbon materials.

[0008] Suitable carbons typically include those from the carbon black family, such as furnace black, superconducting black, acetylene black, and their graphitized forms. Exemplary carbons include Akzo Nobel. EC300J and Cabot XC72R. Alternatively, carbon specifically designed for fuel cell applications, such as those described in WO2013 / 012894, can be used. Alternative materials used as conductive supports include metal oxides or mixed oxides, particularly conductive mixed oxides such as niobium-doped titanium dioxide, phosphorus-doped tin oxide, and mixed platinum group metal oxides or mixed metal oxides, as disclosed in WO2012 / 080726.

[0009] The method of depositing electrocatalysts on a support material affects the electrochemical performance of the supported electrocatalyst. Furthermore, it is important that the method used to deposit electrocatalysts on the support material is efficient and has a low environmental impact. Summary of the Invention

[0010] Therefore, in a first aspect, the present invention provides a method for preparing a catalyst material, said catalyst material comprising a support material and an electrocatalyst dispersed on the support material; said method comprising the following steps:

[0011] i) Provide carrier material; then

[0012] ii) Deposit the silicon oxide precursor onto the carrier material; then

[0013] iii) Perform a heat treatment step to convert the silicon oxide precursor into silicon oxide; then

[0014] iv) Deposit the electrocatalyst or its precursor onto a support material; then

[0015] v) Remove at least some of the silicon oxide.

[0016] To avoid ambiguity, steps i), ii), iii), iv), and v) must be performed in the order i), ii), iii), iv), then v).

[0017] Surprisingly, the inventors have discovered that the catalyst material prepared by this method provides better membrane electrode assembly performance compared to similar catalyst materials prepared by conventional methods that do not include the steps of adding silicon oxide prior to electrocatalyst deposition and subsequently removing at least some of the silicon oxide.

[0018] In a second aspect, the present invention also provides catalyst materials that can be obtained by the method of the present invention.

[0019] In a third aspect, the present invention provides an electrocatalyst layer comprising a catalyst material according to a second aspect of the invention and an ionically conductive polymer, wherein the weight ratio of the ionically conductive polymer to the support material is in the range of 1:3 to 6:5, and includes 1:3 and 6:5. Surprisingly and advantageously, the catalyst material of the present invention can be used in electrocatalyst layers with a reduced amount of the ionically conductive polymer, while maintaining the desired level of electrochemical activity, compared to conventional electrocatalyst layers. Reducing the amount of the ionically conductive polymer improves the performance of the electrocatalyst layer in a membrane electrode assembly because it can lead to higher porosity and higher gas and water transport rates in the electrocatalyst. Attached Figure Description

[0020] Figure 1 This illustrates a membrane electrode assembly containing a cathode electrocatalyst layer comprising a catalyst material prepared by the method of the present invention and a membrane electrode assembly containing a cathode electrocatalyst layer comprising a comparative catalyst material, operating at 0.2 A / cm² under low humidity. 2 1.0A / cm 2 and 1.6A / cm 2 A bar graph of the voltage under the given conditions.

[0021] Figure 2 The membrane electrode assembly containing a cathode electrocatalyst layer comprising a catalyst material prepared by the method of the present invention and the membrane electrode assembly containing a cathode electrocatalyst layer comprising a comparative catalyst material are both at 1.0 A / cm 2 Temperature scan graph below.

[0022] Figure 3 These are oxygen concentration scans under high humidity for membrane electrode assemblies containing a cathode electrocatalyst layer comprising a catalyst material prepared by the method of the present invention and membrane electrode assemblies containing a cathode electrocatalyst layer comprising a comparative catalyst material. Detailed Implementation

[0023] Preferred and / or optional features of the invention will now be set forth. Unless the context otherwise requires, any aspect of the invention may be combined with any other aspect of the invention. Unless the context otherwise requires, any preferred or optional feature of any aspect may be combined with any aspect of the invention, alone or in combination.

[0024] The support material provided in step i) is preferably a conductive carbon support material, preferably in powder form. The support material does not contain an electrocatalyst. The carbon support material can be, for example, carbon black or graphitized carbon black, such as that available from Cabot Corp. XC72R) or Akzo Nobel Carbon black (from the carbon black series), or graphitized forms of these carbon blacks or other commercially available carbon blacks, such as acetylene black (e.g., available from Chevron Phillips (Shawinigan)). )or The carbon support material can also be a material specifically designed for fuel cells, such as those described in WO2013 / 045894. The support material is not limited to carbon support materials and can be any porous support material suitable for supporting electrocatalysts. Therefore, the support material can be a metal oxide or mixed oxide (specifically a conductive mixed oxide, such as niobium-doped titanium dioxide, phosphorus-doped tin oxide, and mixed platinum group metal oxides or mixed metal oxides as disclosed in WO2012 / 080726), a carbide (e.g., tungsten carbide, molybdenum carbide, or titanium carbide, suitably tungsten carbide or titanium carbide), or a nitride (specifically a conductive nitride (e.g., titanium nitride or titanium aluminum nitride)).

[0025] The catalyst material prepared by the method of the present invention comprises an electrocatalyst dispersed on a support material. Therefore, the catalyst material is a supported electrocatalyst, and the term "supported" will be readily understood by those skilled in the art. For example, it should be understood that the term "supported" includes the electrocatalyst being bound or immobilized to the support material by physical or chemical bonds. For example, the electrocatalyst may be bound or immobilized to the support material by ionic or covalent bonds, or by non-specific interactions (such as van der Waals forces). The catalyst material comprises a support material and an electrocatalyst, preferably substantially consisting of a support material and an electrocatalyst, more preferably consisting of a support material and an electrocatalyst.

[0026] The electrocatalyst is preferably suitable for fuel cells or electrolyzers, and more preferably for proton exchange membrane fuel cells or electrolyzers. Therefore, the catalyst material is preferably a fuel cell or electrolyzer catalyst material, and more preferably a proton exchange membrane fuel cell or electrolyzer catalyst material. Therefore, the catalyst material can be a proton exchange membrane fuel cell anode or cathode catalyst material. Therefore, the electrocatalyst is suitably selected from:

[0027] (i) Platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium);

[0028] (ii) Gold or silver;

[0029] (iii) Base metals;

[0030] The electrocatalyst may be an alloy or mixture of one or more of these metals or their oxides. The base metal is tin or a transition metal that is not a noble metal. The noble metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium, or osmium) or gold. Preferred base metals are copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium, and tin. Preferably, the electrocatalyst is not an alloy; that is, preferably, the electrocatalyst is a single-metal electrocatalyst for the reduction of platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, and osmium), preferably platinum. If the electrocatalyst is an alloy, it is preferably an alloy of a platinum group metal (preferably platinum) and a base metal (preferably a base metal as defined above, more preferably nickel or cobalt, most preferably nickel), preferably a binary alloy. The atomic ratio of the platinum group metal (preferably platinum) to the alloy metal is generally in the range of 3:1 to 1:3 and includes 3:1 and 1:3.

[0031] The silicon oxide precursor is any compound capable of being converted into silicon oxide during a heat treatment step. The silicon oxide precursor can be a siloxane compound, i.e., a compound having Si-O-Si bonds. Siloxanes can be formed by the reaction of one or more alkoxysilanes (such as (3-aminopropyl)triethoxysilane (APTES), 3-aminopropyl(diethoxy)methylsilane (APDMES), tetraethyl orthosilicate (TEOS), or methyl triethyl orthosilicate (MTEOS)). Alternatively, siloxane compounds can be formed from silazanes, chlorosilanes, or dimethylaminosilanes. The heat treatment step enables the conversion of the silicon oxide precursor into silicon oxide. The heat treatment step is suitable for being carried out in a reducing atmosphere, such as hydrogen or a mixture of hydrogen and inert gases. Alternatively, a reducing atmosphere can be provided by carbothermal reduction. Preferably, the heat treatment step is carried out in a mixture of hydrogen and inert gases. The heat treatment step is suitable to be carried out in the range of 250°C to 500°C, including 250°C and 500°C, preferably in the range of 290°C to 400°C, including 290°C and 400°C. Preferably, the heat treatment step is carried out as a single heat treatment step, that is, it is not carried out in more than one stage, it is carried out in a single heating stage at the desired temperature (including heating from room temperature to the desired temperature, for example, 1°C / min to 5°C / min), without intermediate stages, such as cooling stages. The silicon oxide present after step iii) is preferably present in an amount of not more than 20 wt% relative to the weight of the carrier material, preferably 15 wt%, more preferably 12 wt%. The silicon oxide present after step iii) is preferably present in an amount of at least 2 wt% relative to the weight of the carrier material, more preferably at least 4 wt%.

[0032] The electrocatalyst can be deposited in step iv) by any method known to those skilled in the art for depositing an electrocatalyst onto a support material, provided that it is compatible with the silica applied in step iii), i.e., it does not expose the material produced in step iii) to conditions that remove silica, such as insufficient alkalinity to dissolve silica. For example, the method using a metal oxide sol and reduction step as described in WO2005 / 123255 can be used. Alternatively, the method using an aqueous solution of a metal acid or salt and a reduction step as described in WO2013 / 045894 can be used. The alloy electrocatalyst can be deposited using any method familiar to those skilled in the art, such as those disclosed in WO2014 / 184546 or WO2017 / 203257. For the avoidance of doubt, the phrase "depositing the electrocatalyst or the precursor of the electrocatalyst onto a support material" in step iv) refers to deposition onto the silica-coated support material prepared in step iii). Preferably, all (e.g., 100%) of the electrocatalyst contained in the catalyst material is deposited in step iv) prior to step v). In this case, the catalyst material is obtained in step v). An alternative to depositing the precursor of the electrocatalyst in step iv) is preferably applicable to aspects where the electrocatalyst is an alloy electrocatalyst. In this alternative, the method includes an additional step vi) after step v) to form the electrocatalyst to obtain the catalyst material. The precursor may suitably be, for example, a constituent metal of the alloy electrocatalyst. In this case, step vi) includes, for example, depositing the remaining metal and forming an alloy according to methods disclosed in WO2014 / 184546 or WO2017 / 203257 to obtain the catalyst material.

[0033] Preferably, substantially all of the silica is removed in step (v), but a small amount of silica is harmless. Therefore, step (v) removes most, preferably substantially all, of the silica from the support material. Fluorination or hydrolysis methods can be used, preferably with alkaline solutions such as hydroxide solutions, particularly tetraethylammonium hydroxide, to remove the silica. Up to and including 5 wt%, suitably up to and including 4 wt%, more suitably up to and including 2 wt%, and even more suitably up to and including 1 wt% of silica relative to the weight of the support material may remain on the catalyst material after removal. Removal of substantially all silica means that, after silica removal, ≥0 wt% but less than 1 wt%, suitably less than 0.5 wt%, and preferably less than 0.01 wt% of silica remains on the catalyst material relative to the weight of the support material.

[0034] The electrocatalyst loading in the catalyst material can be expressed as a weight percentage of the active metal (e.g., platinum group metals) relative to the total weight of the catalyst material, which can be determined using inductively coupled plasma mass spectrometry (ICPMS). The loading may suitably be at least 10 wt% of the active metal, such as platinum group metals. The electrocatalyst loading, based on the total weight of the catalyst material, may suitably not exceed 90 wt% of the active metal, such as platinum group metals, typically not exceed 60 wt% of the active metal, such as platinum group metals, and for example, not exceed 50 wt% of the active metal, such as platinum group metals. In the method of the present invention, this is controlled by controlling the weight ratio of the active metal, such as platinum group metals, to the support material in step iv) of the method.

[0035] The electrocatalyst layer of the present invention comprises an ion-conducting polymer, such as a proton-conducting polymer. Therefore, the ion-conducting polymer may include ionomers, such as perfluorosulfonic acid materials (e.g., (Chemours Company) (Asahi Kasei)、 (Solvay Specialty Polymer) (AsahiGlass Co.) and by The supplied perfluorosulfonic acid ionomer materials), or ionomers based on partially fluorinated or non-fluorinated hydrocarbons as sulfonated or phosphonated polymers, such as those purchased from FuMA-Tech GmbH (as...). Products from the P, E, or K series, or those purchased from JSR Corporation, Toyobo Corporation, etc. Suitablely, the ionomer is a perfluorosulfonic acid, specifically purchased from Chemours Company. series (especially) 1100EW), purchased from Solvay Series (especially) 830EW and 3M 825EW perfluorosulfonic acid ionomers. Surprisingly and advantageously, the catalyst materials of the present invention can be used in electrocatalyst layers with reduced amounts of ionically conductive polymers compared to conventional electrocatalyst layers, while maintaining or substantially improving electrochemical activity. Reducing the amount of ionically conductive polymer improves the performance of the electrocatalyst layer in the membrane electrode assembly because it results in higher porosity and higher gas and water transport rates in the electrocatalyst layer. Therefore, it is preferred that the weight ratio of ionically conductive polymer to support material is in the range of 1:3 to 6:5 and includes 1:3 and 6:5, preferably in the range of 1:1 to 4:5 and includes 1:1 and 4:5, or preferably in the range of 1:2 to 4:5 and includes 1:2 and 4:5, more preferably in the range of 2:3 to 4:5 and includes 2:3 and 4:5.

[0036] The electrocatalyst loading in the electrocatalyst layer will depend on the intended application. In this context, electrocatalyst loading refers to the amount of active metal, such as platinum group metals, in the electrocatalyst layer, expressed in mg / cm³. 2 This is indicated. For example, in the cathode of a fuel cell, the loading is typically at least 0.05 mg / cm³. 2 And not exceeding 1.0 mg / cm 2 In the anode of a fuel cell, the loading is typically at least 0.02 mg / cm³. 2 And not exceeding 1.0 mg / cm 2 When the electrocatalyst is a platinum alloy, for example in the cathode of a fuel cell, the electrocatalyst loading is the amount of platinum per unit area, expressed in mgPt / cm². 2 This is indicated by, for example, in the cathode of a fuel cell containing a platinum-containing electrocatalyst, the electrocatalyst loading is suitably at least 0.05 mg Pt / cm³. 2 Typically, it does not exceed 1.0 mg Pt / cm³. 2 Suitable not exceeding 0.75 mg Pt / cm 2 For example, not exceeding 0.5 mg Pt / cm 2 or not exceeding 0.3 mg Pt / cm 2 In the anode of the fuel cell, the electrocatalyst loading is suitably at least 0.02 mg Pt / cm³. 2 Typically, it is no greater than 1.0 mg Pt / cm³. 2 Suitablely not greater than 0.75 mg Pt / cm 2 For example, not greater than 0.5 mg Pt / cm 2 or not greater than 0.2 mg Pt / cm 2 .

[0037] The electrocatalyst layer may include additional components. For example, the proton exchange membrane fuel cell electrocatalyst layer of the present invention may include an oxygen evolution reaction catalyst and an oxygen hydroxide (anodide) or oxygen reduction reaction (cathode) electrocatalyst. Such additional components may also include, but are not limited to: a hydrogen peroxide decomposition catalyst; hydrophobic additives (e.g., polymers with or without surface treatment, such as polytetrafluoroethylene (PTFE) or inorganic solids) or hydrophilic additives (e.g., polymers or inorganic solids, such as oxides) to control the transport characteristics of reactants and water. The selection of additional components is within the capabilities determined by those skilled in the art based on the application of the electrocatalyst layer.

[0038] To prepare the electrocatalyst layer, the catalyst material of the present invention and any additional components are dispersed in an aqueous solvent and / or an organic solvent to prepare the catalyst ink. If desired, particle breakage is performed by methods known in the art, such as high-shear mixing, grinding, ball milling, microfluidics, or combinations thereof, to achieve a suitable particle size distribution. After preparing the catalyst ink, the ink is deposited onto a substrate (e.g., a gas diffusion layer, an ion-conducting membrane, or a support / transfer substrate) to form the electrocatalyst layer. The ink can be deposited by any suitable technique known to those skilled in the art, including but not limited to gravure coating, slot extrusion (groove, extrusion) coating, screen printing, rotary screen printing, inkjet printing, spraying, painting, bar coating, pad coating, gap coating techniques such as knife or doctor blade coating on rollers, and metering rod coating.

[0039] An electrocatalyst layer can be deposited onto a gas diffusion layer to form the gas diffusion electrode of the present invention. The gas diffusion layer comprises a gas diffusion substrate and, preferably, a microporous layer. When a microporous layer is present, the electrocatalyst layer is deposited onto the microporous layer. Typical gas diffusion substrates include nonwoven paper or mesh comprising a carbon fiber web and a thermosetting resin binder (e.g., TGP-H series carbon fiber paper from Toray Industries Inc., Japan; H2315 series from Freudenberg FCCT KG, Germany; or [other materials] from SGL Technologies GmbH, Germany). Series, or from Ballard PowerSystems Inc. (Series), or woven carbon cloth. Before fabricating electrodes and incorporating them into membrane electrode assemblies, carbon paper, mesh, or cloth may be pretreated to make it more wettable (hydrophilic) or more waterproof (hydrophobic). The nature of any treatment will depend on the type of fuel cell and the operating conditions to be used. The substrate can be made more wettable by impregnating it with a material (such as amorphous carbon black) from a liquid suspension, or more hydrophobic by impregnating the porous structure of the substrate with a colloidal suspension of a polymer (such as PTFE or FEP), followed by drying and heating above the polymer's softening point. A typical microporous layer comprises a mixture of carbon black and a polymer (such as polytetrafluoroethylene (PTFE)).

[0040] In the catalyst-coated ion-conductive membrane of the present invention, the electrocatalyst layer is deposited onto the ion-conductive membrane by directly coating the catalyst ink onto the membrane, or indirectly deposited onto the ion-conductive membrane by transferring it from a transfer substrate, to form the catalyst-coated ion-conductive membrane. The catalyst-coated ion-conductive membrane of the present invention may include a second electrocatalyst layer on its opposite surface, which may be the electrocatalyst layer according to the present invention or other electrocatalyst layers. The ion-conductive membrane may suitably be any membrane suitable for proton exchange membrane fuel cells; for example, the membrane may be based on a perfluorinated sulfonic acid material, such as Nafion. TM (Chemours Company) (Solvay SpecialtyPolymers) (Asahi Glass Group) and Aciplex TM (Asahi Kasei Chemicals Corp.) and by The supplied perfluorosulfonic acid ionomer material. Alternatively, the membrane may be based on sulfonated hydrocarbon membranes, such as those purchased from FuMA-Tech GmbH (…). Products from the P, E, or K series, or those purchased from JSR Corporation, Toyobo Corporation, etc.

[0041] The thickness of the ion-conducting membrane is not particularly limited and will depend on its intended application. For example, a typical fuel cell ion-conducting membrane has a thickness of at least 5 μm, suitably at least 8 μm, and preferably at least 10 μm. A typical fuel cell ion-conducting membrane has a thickness of no more than 50 μm, suitably no more than 30 μm, and preferably no more than 20 μm. Therefore, a typical fuel cell ion-conducting membrane has a thickness in the range of 5 μm to 50 μm and including 5 μm and 50 μm, suitably in the range of 8 μm to 30 μm and including 8 μm and 30 μm, and preferably in the range of 10 μm to 20 μm and including 10 μm and 20 μm.

[0042] The ion-conducting membrane may contain additional components, such as peroxide decomposition catalysts and / or free radical decomposition catalysts and / or recombination catalysts. The recombination catalyst catalyzes the recombination of unreacted H2 and O2, which can diffuse from the anode and cathode of the fuel cell into the ion-conducting membrane to produce water. The ion-conducting membrane may also contain reinforcing materials embedded within the thickness of the membrane, such as planar porous materials (e.g., expanded polytetrafluoroethylene (ePTFE) as described in USRE37307), to provide improved mechanical strength of the ion-conducting membrane, such as enhanced tear resistance and reduced dimensional changes during hydration and dehydration, and thus further increase the durability of the membrane electrode assembly and the lifespan of the fuel cell incorporating the catalytic ion-conducting membrane of the present invention. Other methods for forming the reinforced ion-conducting membrane include those disclosed in US 7,807,063 and US 7,867,669, in which the reinforcement is a rigid polymer membrane, such as polyimide, in which multiple pores are formed and then filled with PFSA ionomer. The selection of additional components is within the capabilities of those skilled in the art, depending on the application of the electrocatalyst layer.

[0043] Any reinforcement present may extend over the entire thickness of the ion-conducting film, or over only a portion of its thickness. It should be understood that the thickness of the ion-conducting film extends perpendicular to its surface, for example, in the z-direction of the penetrating plane. It may also be advantageous to reinforce the periphery of the first and second surfaces of the ion-conducting film to a greater extent than the center plane of the first and second surfaces. Conversely, it may be desirable to reinforce the center of the first or second surface of the ion-conducting film to a greater extent than the periphery of the first or second surface.

[0044] When an electrocatalyst layer is created on a transfer substrate by coating a catalyst ink onto the transfer substrate, it forms the catalytic transfer substrate of the present invention. Additional layers may be deposited on the exposed surfaces of the electrocatalyst layer before the transfer substrate is removed; for example, any suitable known deposition technique described above regarding the deposition of the electrocatalyst layer may be used to apply an ionically conductive ionomer layer from the dispersion of the ionomer. Additional layers may be added as needed, for example as described in PCT patent application number GB2015 / 050864. The transfer substrate is removed from the electrocatalyst layer at an appropriate time. The transfer substrate may be formed of any suitable material from which the electrocatalyst layer can be removed without damage. Examples of suitable materials include fluoropolymers (such as polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymers (PFA), fluorinated ethylene propylene (FEP – a copolymer of hexafluoropropylene and tetrafluoroethylene)) and polyolefins (such as biaxially oriented polypropylene (BOPP)).

[0045] As those skilled in the art will understand, the membrane electrode assembly of the present invention can be constructed in various ways, provided that it includes at least one electrocatalyst layer of the present invention. For example, the membrane electrode assembly may include a catalyst-coated ion-conductive membrane of the present invention, the catalyst-coated ion-conductive membrane comprising two electrocatalyst layers, wherein at least one electrocatalyst layer is the electrocatalyst layer of the present invention, and a gas diffusion layer is applied to each electrocatalyst layer. Alternatively, the membrane electrode assembly may include an ion-conductive membrane sandwiched between two gas diffusion electrodes, wherein at least one gas diffusion electrode is the gas diffusion electrode of the present invention. The membrane electrode assembly may also include a catalyst-coated ion-conductive membrane having one electrocatalyst layer, and a gas diffusion electrode comprising an opposite surface of the ion-conductive membrane, wherein either or both of the electrocatalyst layer and the gas diffusion electrode are the electrocatalyst layer and / or the gas diffusion electrode of the present invention.

[0046] Example

[0047] Preparation of catalyst materials

[0048] A catalyst material consisting of 50 wt% Pt / C was prepared according to the following method according to the present invention. 10 g of carbon black was slurried in 1 L of deionized water, and 150 ml of 35% ammonia solution was added under stirring. The mixture was heated to 60 °C, and then 7.64 g of tetraethyl orthosilicate (TEOS) was added. The mixture was stirred for 2 hours, then cooled to ambient temperature, filtered, and washed with deionized water. The resulting solid was dried overnight at 105 °C, and then heated to 350 °C at a heating rate of 2 °C / min under 5% H2 / N2 and held for 3 hours to convert the SiO2 precursor to SiO2. After cooling to ambient temperature, the calcined, SiO2-coated carbon intermediate was dispersed in 1 L of deionized water according to the procedure disclosed in WO2005 / 123255, and 10 g of Pt was added. The sample was collected by filtration and washed with deionized water, and then dispersed again in 1 L of deionized water. Add 210 ml of 35% tetraethylammonium hydroxide solution with stirring, and stir the mixture overnight at ambient temperature. Then collect the product by filtration, wash with deionized water, and dry overnight at 105°C.

[0049] The comparative catalyst material used is 50% Pt / C, wherein the carbon support is carbon specifically designed for fuel cells as described in WO2013 / 045894, and it is prepared by a conventional deposition process without the use of silicon oxide.

[0050] Fabrication of membrane electrode assembly

[0051] The catalyst material prepared by the method of the present invention and comparative catalyst materials are used in the cathode electrocatalyst layer. This is achieved by using PFSA ionomer dispersed in a 20% water / 80% propan-1-ol mixture (… A cathode electrocatalyst layer ink (cathode ink) was prepared by wetting the catalyst material with a 1100EW (1100EW) wettase. The mixture was mechanically stirred using a top-mounted stirrer until all the catalyst material was wetted and dispersed in the liquid. The ink was then ball-milled to form a well-dispersed ink. Three types of such inks were prepared:

[0052] EL1: Contains a catalyst prepared according to the present invention and 70% by weight of an ionomer based on the support material.

[0053] EL2: Contains 70% ionomer by weight of the catalyst material and the support material.

[0054] EL3: Contains 90% ionomer by weight of the catalyst material and the support material.

[0055] By using PFSA ionomer dispersed in an 83% water / 17% propan-1-ol mixture ( Anode electrocatalyst layer ink (anodine ink) was prepared by wetting the anode catalyst material (1100EW). The anode electrocatalyst material was 20% Pt / XC72R. The mixture was mechanically stirred using a top-mounted stirrer until all the catalyst was wetted and dispersed in the liquid. The ink was then processed using an Eiger ball mill to form a well-dispersed ink.

[0056] An active area of ​​50 cm² was prepared by depositing anolyte and cathode inks EL1, EL2, and EL3 onto a PTFE sheet to form an electrocatalyst layer, and then transferring a suitable layer to either side of a PFSA-reinforced film (20 μm thick) at a temperature between 150°C and 200°C. 2 The catalyst is coated with an ion-conducting membrane. The catalyst loading of the cathode electrocatalyst is 0.2 mg Pt / cm³. 2 The loading of the anode electrocatalyst is 0.1 mg Pt / cm³. 2 .

[0057] A gas diffusion layer was applied to each surface of the ion-conducting membrane coated with each catalyst to form complete membrane electrode assemblies MEA1, MEA2, and MEA3. The gas diffusion layer used was carbon fiber paper with a hydrophobic microporous layer containing carbon and PTFE applied to the surface in contact with the catalyst-coated ion-conducting membrane. MEA1 constitutes the cathode electrocatalyst layer formed by EL1, MEA2 constitutes the cathode electrocatalyst layer formed by EL2, and MEA3 constitutes the cathode electrocatalyst layer formed by EL3.

[0058] Membrane electrode assembly performance testing

[0059] Pure oxygen, air, or synthetic air are used as cathode reactants, and pure H2 is used as anode reactant (all gases are 99.9% pure).

[0060] At current density > 0.2 A cm -2 When using the stoichiometric flow rates of the reactants at the anode (s=2 for H2, s=2 for O2, s=9.5 for air) and cathode, at a current density <0.2 A cm⁻¹ -2 A constant flow rate (corresponding to 0.2 A cm) is used. -2 (Stoichiometric flow rate). The reactants were humidified by bubbling gas through a water reservoir, the temperature of which was calibrated to produce the desired relative humidity (RH) value. Humidity and cell pressure were measured at the inlets of both electrodes. Cell resistance as a function of current density (i.e., the sum of proton conduction resistance in the membrane and various electronic, bulk, and contact resistances) was determined using a 1 kHz AC perturbation. For each current density value, the cell voltage was stabilized for 10 minutes before recording. Testing was performed using multi-channel serpentine flow field plates (two and three parallel channels for the anode and cathode, respectively) made from machined, sealed graphite blocks.

[0061] By applying 500 mA cm at 100 kPa gauge pressure, 100% RH and 80°C in H2 / air... -2 The MEA is regulated using a constant current density. The cell voltage is monitored until a stable value is observed. Unless otherwise specified, the regulation process lasts for 2 hours. The cathode catalyst layer is then exposed to a series of cathode starvation steps, followed by exposure at 500 mA / cm². -2 The cathode was held for 2 hours until a stable voltage was observed. A cathode starvation step (purging the cathode chamber with pure nitrogen) reduced the cathode voltage to below 0.1V and was intended to provide an electrochemical cleaning step for the cathode catalyst, after which its activity under H2 / O2 conditions was measured. The activity was measured in H2 ( / O2 and air) at an inlet gauge pressure of 100 kPa, 80°C, and a relative humidity of 100% Rh or 30% RH at the cell inlet for 50 cm⁻¹. 2 Polarization curves in a single cell. The cell current density was held for 10 minutes at each point, and the cell voltage was averaged during the last minute of this holding period. The cell voltages under H2 / air shown in the figure are recorded in a decreasing voltage direction from low current to high current. The polarization curves under H2 ( / O2 air) are not corrected for internal (ohmic) resistance.

[0062] Under H2 / air conditions, at 50cm 2Temperature scanning was performed in a single cell. Anode and cathode stoichiometry were set to 2, and the anode and cathode pressures at the cell inlet were controlled at 100 kPa gauge pressure. The anode and cathode humidifier dew point was controlled at 53°C, while the cell temperature varied between 35°C and 90°C. This achieved very high humidity at low temperatures and very low humidity at high temperatures. Temperature scans were recorded from low to high temperatures at the specified 53°C dew point, without correcting for the cell voltage for internal resistance. The current density was maintained at 1000 mA / cm² at each temperature. 2 The voltage was averaged using data recorded during the last minute of the hold phase, which lasted for 10 minutes.

[0063] At 50cm 2 Oxygen concentration scanning was performed in a single cell. The current density was fixed at 1000 mA / cm². 2 The oxygen concentration was changed from 100% O2 to 75%, 50%, 30%, 21%, and 10% using N2 as a dilution gas. Battery humidity was controlled at 100% RH, and battery temperature was maintained at 80°C. Anode and cathode stoichiometry were set to 2 and 10, respectively. The current density was maintained for 10 minutes at each oxygen concentration, and the voltage was averaged using data recorded in the last minute of the hold phase. The oxygen concentration scan was not corrected for internal resistance.

[0064] Experimental results

[0065] Figure 1 The results were compared between MEA 1, MEA 2, and MEA 3 under hot and dry conditions (80°C and 30% RH, 50 kPa inlet gauge pressure) at 0.2 A / cm. 2 1.0A / cm 2 and 1.6A / cm 2 The performance of MEA 1, using the catalyst material prepared by the method of the present invention, is significantly better than that of MEA 2, which is an equivalent MEA using a catalyst material prepared by conventional methods, at all current densities. A conventional method to improve performance under hot, dry conditions is to add a higher percentage of ionomer to the cathode catalyst layer. This treatment was performed on MEA 3, which contains the comparative catalyst material on the cathode side. As expected, performance was improved compared to MEA 2, but still lower than MEA 1 at all current densities. This indicates that the method of the present invention allows for the use of less ionomer while achieving better performance than MEAs prepared with comparative catalyst materials across the entire current density range.

[0066] Figure 2 The display shows that at 1.0 A / cm 2At moderate current densities, MEA 1, containing a cathode electrocatalyst layer comprising the catalyst material prepared by the method of this invention, exhibits better performance (higher voltage) than MEA 3, which contains an electrocatalyst layer comprising conventional catalyst materials, within the range of hot, dry conditions (65°C to 90°C, dew point 53°C). Particularly surprising is that MEA 1, where the cathode electrocatalyst layer contains only 70 wt% ionomers relative to the carbon support material, performs better than MEA 3, where the cathode electrocatalyst layer contains 90 wt% ionomers relative to the carbon support material. Generally, MEAs with higher ionomer levels within the cathode are expected to perform better under hot, dry conditions. Therefore, for the catalyst material prepared by the method of this invention, less ionomer can be used, which implies higher porosity and higher gas and water transport rates in the electrocatalyst layer.

[0067] like Figure 3 As shown, MEA 1 performs better than MEA 3 at lower oxygen concentrations (i.e., closer to actual operating conditions). This demonstrates the beneficial effects on the electrochemical performance associated with the catalyst materials prepared using the method of this invention.

Claims

1. A method for preparing a catalyst material, said catalyst material comprising a support material and an electrocatalyst dispersed on said support material; the method comprising the following steps: i) Provide a carrier material, wherein the carrier material is a conductive carbon material; Then ii) Deposit the silicon oxide precursor onto the carrier material; then iii) A heat treatment step is performed at a temperature ranging from 250°C to 500°C, including both 250°C and 500°C, to convert the silicon oxide precursor into silicon oxide; then iv) Depositing the electrocatalyst or a precursor of the electrocatalyst onto the support material, wherein the electrocatalyst is selected from platinum group metals, gold or silver, base metals, or alloys or mixtures containing one or more of these metals or their oxides; then v) Remove at least some of the silicon oxide.

2. The method according to claim 1, wherein in step v), silicon oxide is removed such that ≥0 wt% to <1 wt% of silicon oxide relative to the weight of the support material remains on the catalyst material.

3. A catalyst material that can be obtained by the method according to claim 1 or 2.

4. An electrocatalyst layer comprising an ion-conducting polymer and the catalyst material according to claim 3, wherein the weight ratio of the ion-conducting polymer to the support material is in the range of 1:3 to 6:5 and includes 1:3 and 6:

5.

5. A catalyst-coated ion-conducting membrane comprising the electrocatalyst layer and the ion-conducting membrane according to claim 4.

6. A catalytic transfer substrate comprising a transfer substrate and an electrocatalyst layer according to claim 4.

7. A gas diffusion electrode comprising a gas diffusion layer and an electrocatalyst layer according to claim 4.

8. A membrane electrode assembly comprising an electrocatalyst layer according to claim 4, an ion-conducting membrane coated with a catalyst according to claim 5, or a gas diffusion electrode according to claim 7.

9. A fuel cell comprising an electrocatalyst layer according to claim 4, an ion-conducting membrane coated with a catalyst according to claim 5, a gas diffusion electrode according to claim 7, or a membrane electrode assembly according to claim 8.

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