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EP-4735172-A1 - CATALYST POWDER SUITABLE IN PARTICULAR FOR PRODUCTION OF AN ANODE CATALYST FOR PROTON EXCHANGE MEMBRANE WATER ELECTROLYSIS, AND PROCESS FOR PRODUCING SUCH A CATALYST POWDER

EP4735172A1EP 4735172 A1EP4735172 A1EP 4735172A1EP-4735172-A1

Abstract

The present invention relates to a catalyst powder suitable for production of an anode catalyst for proton exchange membrane water electrolysis, having catalyst particles (1) having a core (2) of a semiconductive material, and a catalyst shell layer (3) that fully covers the core and comprises iridium and/or iridium oxide.

Inventors

  • HOFFMEISTER, Darius
  • VAN PHAM, Chuyen
  • FINGER, Selina
  • HUTZLER, Andreas
  • THIELE, SIMON

Assignees

  • Forschungszentrum Jülich GmbH

Dates

Publication Date
20260506
Application Date
20240614

Claims (11)

  1. 1. Catalyst powder suitable for producing an anode catalyst for proton exchange membrane water electrolysis, comprising catalyst particles (1) with a core (2) made of a semiconducting material and a catalyst coating layer (3) completely covering the core and comprising iridium and/or iridium oxide.
  2. 2. Catalyst powder according to claim 1, characterized in that the semiconducting material is titanium oxide (TiO2) or doped tin oxides.
  3. 3. Catalyst powder according to claim 1 or 2, characterized in that the cores (2) are formed from spherical carrier particles, rod-shaped carrier particles or two-dimensional carrier particles.
  4. 4. Catalyst powder according to one of the preceding claims, characterized in that the cores (2) have a specific surface area in the range of 1 to 10 m 2 /g.
  5. 5. Catalyst powder according to one of the preceding claims, characterized in that the catalyst coating layers (3) have a layer thickness in the range of 1 to 20 nm.
  6. 6. Catalyst powder according to one of the preceding claims, characterized in that the iridium content of the catalyst coating layers (3) is in the range from 5 to 50 wt.%.
  7. 7. Catalyst powder according to one of the preceding claims, characterized in that further iridium and/or iridium oxide particles (4) are arranged on the catalyst coating layers (3).
  8. 8. Process for producing catalyst powder according to one of the preceding claims, comprising the steps: a) producing an aqueous solution of Ir 3+ ions by dissolving IrCh or other water-soluble iridium precursors/iridium salts in water; b) producing a dispersion of carrier particles, in particular TiC carrier particles, in water by adjusting the pH using a base, for example KOH, and subsequent dispersion, for example by means of ultrasound; c) adding the solution produced in step a) to the dispersion produced in step b), adjusting the pH using a base and preferably adding a so-called hole scavenger, for example isopropanol; d) depositing metallic or oxidic iridium on the surface of the carrier particles by irradiating the reaction solution produced in step c) with UV radiation, preferably having a wavelength of 254 nm; e) filtering, washing, drying and grinding the powder produced in step d); and f) oxidation of the deposited metallic or oxidic iridium at a temperature in the range of 100-600 °C, preferably 350 °C, under an oxygen-containing atmosphere.
  9. 9. The method according to claim 8, characterized in that after carrying out step d), a reduction of the remaining iridium ions is carried out as a second synthesis step, for example by heating the reaction solution, so that the hole scavenger acts as a reducing agent.
  10. 10. The method according to claim 8 or 9, characterized in that after carrying out step d), additional iridium and/or iridium oxide particles (4) are applied.
  11. 11. Use of catalyst powder according to one of claims 1 to 7 for producing an anode catalyst for proton exchange membrane water electrolysis (PEMWE).

Description

DESCRIPTION Catalyst powder which is particularly suitable for producing an anode catalyst for proton exchange membrane water electrolysis, and process for producing such a catalyst powder The present invention relates to a catalyst powder which is particularly suitable for producing an anode catalyst for proton exchange membrane water electrolysis, and to a process for producing such a catalyst powder. One task of catalysts, for example, is the electrocatalysis of the oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). In an electrolyzer, water is split into its components hydrogen and oxygen, from which their molecular gases are then produced. Climate change is an ever-increasing challenge and its negative impacts can only be slowed if humanity is able to generate energy from sources other than fossil fuels. This means, for example, the use of renewable energy sources. However, in order to effectively transform our energy supply, a large-scale method of energy storage must be developed. Current research suggests that this can be achieved by using different technologies in parallel, such as batteries, e-fuels and hydrogen-related technologies. It is expected that around 50% of energy storage will be provided by hydrogen-based Technologies should be covered. For the production of hydrogen from water, proton exchange membrane water electrolysis is a promising candidate due to its high production rates, also referred to as "PEMWE" for short. However, one of the biggest challenges in PEMWE is the high demand for precious metals, especially iridium, with an annual global production of only about 7 to 8 tonnes. Iridium is usually used as an anode catalyst for OER. Since research into precious metal-free catalysts for the anode side has not yet produced any industry-relevant innovations, the focus in the development of new catalysts for the near future should be on reducing the iridium loading in the catalyst layer as much as possible. Industrially, catalyst powders with an iridium content between 75 wt.% and 100 wt.% are typically used for PEMWE. 0-25 wt.% titanium dioxide (TiO2) can be added as a carrier material, for example. These catalysts are normally used to produce anodic catalyst layers with an iridium loading of 1-2 mgi r cm- 2. However, since iridium is expensive and, above all, only available in finite quantities, the iridium loading must be drastically reduced for large-scale expansion of this technology. When reducing the iridium loading, there is a limit in commercially available catalysts below which the catalyst layers result in a significant loss of performance of the PEMWE. According to the current state of research, this limit is around 0.5 mgi r cm- 2 . If the iridium loading in the layer is further reduced, this results in a significantly higher cell voltage and thus significantly higher losses when using electrical energy to generate hydrogen. This loss of performance is attributed to the fact that the layers become too thin and inhomogeneous. This means that parts of the iridium present in the layer can no longer be electrically contacted and thus no (electro)catalytic reaction can take place there. The utilization of the catalyst decreases accordingly. In order to reduce the iridium loading to below 0.5 mgi r cm- 2 and at the same time produce a catalyst layer with sufficient layer thickness, the iridium content in the catalyst powder can be reduced, ie replaced by more carrier material. However, catalysts with inorganic oxides such as TiO2 as the carrier material suffer from the poor conductivity of the carrier, since electrical percolation is no longer possible with a low iridium content. This low conductivity reduces the composite conductivity of the catalyst (catalyst + carrier), which in turn leads to higher resistance-related energy losses. Therefore, the iridium content in the catalyst powder is typically at least 30 wt.%, but tends to be significantly higher at 75-100 wt.%. Based on this prior art, it is an object of the present invention to provide a more efficient catalyst with preferably simultaneously low iridium content for use as an anode catalyst in PEMWE. To achieve this object, the present invention provides a catalyst powder which is particularly suitable for producing an anode catalyst for proton exchange membrane water electrolysis, comprising catalyst particles with a core made of a semiconducting material and a catalyst coating layer completely covering the core comprising iridium and/or iridium oxide, wherein the catalyst powder consists in particular of such catalyst particles. Such a catalyst powder is therefore based on iridium and/or iridium oxide as the active material. It should have as low an iridium content as possible, but at the same time enable a high utilization of the iridium content, which leads to a high iridium-specific power density. This means that the iridium loading of a catalyst layer produced with the cata