Novel Ru-Based PEM Electrolysis Catalyst – Development from the Nano- to the Industrial-Scale

For the de-fossilization of sectors like chemicals, steel, and transportation, green H 2 generated via water electrolysis provides a path towards net-zero. The broad use of H 2 across hard-to-abate sectors confirms the urgent need for green hydrogen at scale. Within water electrolysis, there are several competing technologies: the so-called solid oxide electrolysis cell (SOEC), alkaline water electrolysis (AEL) and polymer electrolyte membrane electrolysis (PEM EL). Here, the latter shows significant benefits, such as high current density operation (> 2 A/cm 2 ) and thus a smaller footprint, highly dynamic operation mode, high gas purity, and generation of pressurized hydrogen. However, at present, PEM EL requires precious metal catalysts; in particular, the O 2 evolution on the anode currently relies on iridium, a metal which is rather scarce and expensive 1. To meet the demand of iridium with respect to the announced increase in electrolyzer capacities in the multi-GW range, material innovation to reduce the use of this precious metal must be implemented. Successful catalyst and electrode developments have already been demonstrated in the BMBF funded project Kopernikus P2X, whereby loadings of approx. 0.3 mg/cm 2 (< 0.1 g/kW 1 ) have been achieved without any significant losses in activity over time 2, 3. Here, we present a material innovation in the form of Ru-based electrocatalysts with a significantly reduced Ir content. This ruthenium-iridium oxide can be adjusted in a wide range of Ir content down to less than 15 wt.% (Ir). Consequently, iridium-based electrode loadings of less than 0.1 mg/cm 2 and mass activities of about 3,500 A/g are feasible. Moreover, in accelerated degradation tests those mixed-oxides have demonstrated the often-missing stability by showing low degradation rates, similar to that of pure IrO 2 , in up to 30,000 potential-induced stress cycles. This achievement stems from a remarkable screening approach that combines synthesis, characterization and testing at the nanoscale at Mattiq, and on industrial scale in the multi-gram range at Heraeus Precious Metals GmbH & Co. KG. Remarkably the alignment of degradation testing on both scales showcases the power of the applied method, providing a blueprint for high throughput screening for future material developments, both within water electrolysis and beyond. References 1 “Iridium Quaterly Market Report“, SFA Oxford (2021) 31 2 M. Bernt, A. Hartig-Weiß, M.F. Tovini, H.A. El-Sayed, C. Schramm, J. Schröter, C. Gebauer, H.A. Gasteiger, Chem. Ing. Tech. 92, 31 (2020) 3 M. Möckl, M.F. Ernst, M. Kornherr, F. Allebrod, M. Bernt, J. Byrknes, C. Eickes, C. Gebauer, A. Moskovtseva, H.A. Gasteiger, J. Electrochem. Soc. 169, 064505 (2022)