Joost van Himste, Paul Poodt, SparkNano B.V. Eindhoven, The Netherlands
Proton Exchange Membrane Water Electrolysis (PEMWE) is a commonly used technique to produce green hydrogen from water. A massive upscaling of PEMWE installations is required in the coming decade to keep up with the foreseen demand for green hydrogen. State-of-the-art PEM electrolyzers make use of iridium-based electrocatalyst layers with iridium loadings of 1-2 mg/cm². The high cost and limited availability of iridium will limit the scalability of PEMWE if the iridium loading cannot be reduced.
Atomic Layer Deposition can be used to apply thin and highly conformal IrO₂ films on porous substrates with atomic-scale control of the amount of material that is deposited. When applied to PEM electrolyzers, this can be used to significantly reduce the loading of IrO₂. Recently, IrO₂ catalyst layers for PEM electrolyzers applied by Spatial ALD with iridium loadings well below 0.1 mg/cm² have been reported.
We will present plasma enhanced Spatial ALD of iridium oxide and metallic iridium films using a new iridium precursor developed by Air Liquide Advanced Materials. The electrocatalytic efficiency and stability has been characterized using RDE, showing that IrO₂ films of just a few nanometer demonstrate an excellent catalytic activity and stability. IrO₂ films have been conformally deposited on high surface area titanium porous transport layers (PTL’s) as well as Nafion membranes. First demonstrations on full PEM stack scale show that Spatial ALD can enable iridium loads 10-100x lower than the state of the art while demonstrating an excellent stability in accelerated stress tests.
We will also discuss how Spatial ALD of IrO₂ films can be up-scaled to mass production, with emphasis on efficiency or precursor utilization and precursor recovery for recycling.