Operando XAS In a Proton Exchange Membrane Water Electrolyser Under Industrially Relevant Conditions

Optimising the performance of proton exchange membrane water electrolysers (PEMWEs) requires mechanistic insight into electrocatalyst behaviour under device-relevant conditions. Here, we report an operando PEMWE for synchrotron XAS with an incorporated reference electrode, enabling catalyst structure and oxidation state to be correlated directly with anode potential. Electrochemical benchmarking against a conventional PEMWE with identical catalyst-coated membranes shows that representative anode performance is achieved during synchrotron XAS. The evolution of a hydrated IrOx anode catalyst and a Pt cathode catalyst is thereby followed throughout break-in and operation at current densities extending beyond 2 A cm−2 (4000 A g−1 IrOx ). The reference electrode enables direct comparison of catalyst behaviour across cell geometries, with the Ir oxidation state response found to be comparable between a three-electrode flow cell with a gas diffusion electrode and the PEMWE below onset of the Oxygen Evolution Reaction (OER). During OER, the PEMWE reaches ∼30-fold higher massnormalised current densities and shows continued Ir oxidation with increasing anode potential. The absence of an Ir oxidation state plateau at these high potentials suggests that prior reports of such a plateau may reflect incomplete catalyst utilisation under more transport-limited conditions, rather than an intrinsic feature of Ir oxidation behaviour.