Platinum Oxide Formation under Oxygen Evolution Reaction Conditions

Electrocatalyst degradation, often caused by oxidative processes, forms a large barrier for the wide-spread application of electrolysers and fuel cells, which are crucial for a sustainable energy society. A detailed understanding of the catalyst surface structure under oxygen evolution reaction (OER) conditions is, therefore, required to design more stable catalysts. Here, we study the oxidation of a Pt(111) model electrode under operando conditions combining High-Energy Surface X-ray Diffraction (HE-SXRD) with a Rotating Disk Electrode (RDE) in a unique experimental setup. This novel approach allows us to follow the atomic structure of the electrode/electrolyte interface under oxygen evolution reaction conditions under hitherto unexplored potential regimes. We find that the Pt(111) surface gets electro-oxidized in a layer-by-layer fashion, which is the best scenario in terms of electrode stability. From ex situ X-ray Reflectivity (XRR) and X-ray Photoelectron Spectroscopy (XPS) measurements we find that a sub-nm thick, PtO₂ oxide film is forming, which deactivates the surface and leads to surface roughening after subsequent dissolution. Our results provide important insight for the operation of fuel cells and electrolysers under intermittent conditions of renewable energies.