EP-4738479-A1 - METHOD FOR PRODUCING A CATALYST LAYER BY MEANS OF AN INK SUBJECTED TO CONTINUOUS REMOVAL OF CONTAMINANT PARTICLES

Abstract

According to the present invention there is provided a method of producing a catalyst-containing layer for a fuel cell or electrolyser. The method comprising the steps of: providing a flow of ink, the ink comprising catalyst particles, an ion-conducting polymer and a liquid medium; conveying the flow of the ink through a density separator configured to separate contaminant particles from the flow of ink, wherein the contaminant particles are more dense than the catalyst particles; and then coating the ink onto a substrate.

Inventors

• The designation of the inventor has not yet been filed

Assignees

• Johnson Matthey Hydrogen Technologies Limited

Dates

Publication Date

20260506

Application Date

20241030

Claims (13)

1. A method of producing a catalyst-containing layer for an electrochemical device, the method comprising the steps of: providing a flow of ink, the ink comprising catalyst particles, an ion-conducting polymer and a liquid medium; conveying the flow of ink through a density separator configured to separate contaminant particles from the flow of ink, wherein the contaminant particles are more dense than the catalyst particles; and then coating the ink onto a substrate.
2. A method according to claim 1, wherein the flow of ink has a substantially laminar flow while flowing through the density separator.
3. A method according to claim 1 or 2, wherein the flow of ink has a first flow speed prior to entering the density separator, and a second flow speed while the ink flows through the density separator, wherein the second flow speed is slower than the first flow speed.
4. A method according to any previous claim, wherein the density separator is a settling chamber, preferably a gravitational settling chamber.
5. A method according to any previous claim, wherein the density separator comprises an expansion chamber.
6. A method according to any previous claim, wherein the flow of ink is conveyed through the density separator a plurality of times, preferably at least 5 times, prior to the step of coating the ink onto the substrate.
7. A method according to any previous claim, wherein the method further comprises milling the ink using a milling apparatus, and then conveying the flow of ink from the milling apparatus to the density separator.
8. A method according to claim 7, wherein the method comprises recirculating the flow of ink through the milling apparatus via the density separator.
9. A method according to any previous claim, wherein the substrate is an ion-conducting membrane.
10. A method according to any previous claim, wherein the catalyst-containing layer is an electrocatalyst layer.
11. A method according to any previous claim, further comprising the subsequent step(s) of: (a) applying an ion-conducting membrane to the catalyst-containing layer; and/or (b) applying a gas diffusion layer or a porous transport layer to the catalyst-containing layer.
12. A continuous milling system comprising: a milling apparatus for milling an ink comprising catalyst particles, an ion-conducting polymer, and a liquid medium; a density separator; and a recirculation loop for recirculating a flow of the ink through the milling device via the density separator, wherein the density separator is configured to separate contaminant particles from the flow of ink, wherein the contaminant particles are more dense than the catalyst particles.
13. An ink coating system for producing a catalyst-containing layer, the ink coating system comprising: an ink container for an ink; a density separator configured to separate contaminant particles from a flow of ink, wherein the contaminant particles are more dense than the catalyst particles; and a coating device comprising an ink dispenser for depositing the catalyst ink onto a substrate; wherein the density separator is fluidly connected to the ink container and downstream of the ink container, and the coating device is fluidly connected to the density separator and downstream of the density separator.

Description

Field of the Invention This invention relating to a method of producing a catalyst-containing layer, such as an electrocatalyst layer, for an electrochemical device, such as a fuel cell or electrolyser. The invention also relates to methods of producing catalyst-coated membranes, gas diffusion electrodes, and membrane electrode assemblies. Background of the Invention A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g. hydrogen, an 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 the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode. Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water. An electrolyser is an electrochemical device for electrolysing water to produce high purity hydrogen and oxygen. Electrolysers can operate in both alkaline and acidic systems. Those electrolysers that employ a solid proton-conducting polymer electrolyte membrane, or proton exchange membrane (PEM), are known as proton exchange membrane water electrolysers (PEMWEs). Those electrolysers that utilise a solid anion-conducting polymer electrolyte membrane, or anion exchange membrane (AEM), are known as anion exchange membrane water electrolysers (AEMWEs). A principal component of the fuel cell or water electrolyser is the membrane electrode assembly (MEA). The MEA is typically composed of five layers. The central layer is the polymer ion-conducting membrane. On either side of the ion-conducting membrane there is an electrocatalyst layer, containing an electrocatalyst designed for the specific electrolytic reaction. Finally, adjacent to each electrocatalyst layer there is a gas diffusion layer, and/or a porous transport layer. The gas diffusion layer (or porous transport layer) allows the reactants to reach the electrocatalyst layer and conduct the electric current that is generated by the electrochemical reactions. The gas diffusion layer (or porous transport layer) is porous and electrically conducting. The electrocatalyst layers generally comprise an electrocatalyst material comprising a metal or metal alloy suitable for an oxidation reaction (e.g. fuel oxidation) or a reduction reaction (e.g. oxygen reduction reaction), depending on whether the layer is to be used at the anode or cathode. The electrocatalyst is typically based on platinum or platinum alloyed with one or more other metals. The platinum or platinum alloy catalyst can be in the form of unsupported nanoparticles (such as metal blacks or other unsupported particulate metal powders) but more conventionally the platinum or platinum alloy is deposited as higher surface area nanoparticles onto a high surface area conductive carbon material, such as a carbon black or heat treated versions thereof. Anode catalysts for PEMWEs typically comprise iridium or iridium oxide (IrOx) materials, or oxides containing both iridium and ruthenium. The electrocatalyst layers also generally comprise a proton conducting material, such as a proton conducting polymer, to aid transfer of protons from the anode catalyst to the membrane and or from the membrane to the cathode catalyst. The MEA can be constructed by a number of known methods. A common method involves depositing one or both of the catalyst layers on a decal transfer substrate and transferring the catalyst layers to either side of the ion-conducting membrane. Subsequently, a gas diffusion layer (or porous transport layer) is applied to the electrocatalyst layer. Alternatively, a catalyst layer can be applied to a gas diffusion layer (or porous transport layer) to form a gas diffusion electrode (or porous transport electrode), which is then combined with the ion-conducting membrane. As a further alternative, catalyst layers can be coated directly onto either side of an ion-conducting membrane. A membrane electrode assembly can be prepared by any combination of these methods e.g., one catalyst layer is applied to the ion-conducting membrane to form a catalyst-coated ion-conducting membrane, and the other catalyst layer is applied as a gas diffusion electrode. The catalyst layers can be deposited using a catalyst ink which typically comprises an electrocatalyst, an ion-conducting polymer, solvents/dispersants and/or diluents, and any agents or additives desired to be include