Reliable testing of acidic OER catalysts in GDE half-cell set-up at industrially-relevant current densities

• Modification of GDE half-cell set-up for reliable OER data acquisition in acidic conditions and at industrially-relevant current densities • Effect of membrane material, GDL material, flow field, and reactant feed on recorded performance data • Detailed studies of OER catalysts for PEM water electrolysis; outlook on AEM water electrolysis testing Production of green hydrogen from acidic and, in the future, alkaline membrane water electrolysers, is an important puzzle piece in our future energy landscape. To make the technology economically viable, novel catalysts are routinely investigated in a small-scale rotating disk electrode electrochemical cell, facing well-known limitations with respect to catalyst layer thickness, 3D porous structure and mass transport during testing. The gas diffusion electrode half-cell set-up is one strategy to remedy these limitations, as it offers testing at industrially relevant current densities in a sample environment mimicking the real electrolyser conditions. Although the GDE half-cell set-up has already been successfully applied in testing of oxygen reduction and carbon dioxide electroreduction catalysts, its application in water electrolysis is still scarce and further insight into the optimal set-up components, robust sample preparation and stable testing conditions is required. In this paper, we aim to elucidate the effect of different flow fields in a gas diffusion half-cell comparing different gas diffusion layers, and reactant feeds during the oxygen evolution reaction in acidic media. In-situ X-ray absorption spectroscopy studies will also be used to unravel the effect of high current densities on the gas diffusion electrodes, which are more realistic towards water electrolyser operations.