Preprint of "Oxygen Evolution Evolving Catalysts Based on activated Ru–Ir Alloy Electrodes - An in-situ Soft XAS and operando XPS Study"

In-situ formation and activation of Ru–Ir alloys into oxygen evolving catalysts for PEM electrolyzers were studied by operando soft X-ray absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron Spectroscopy. The anodic activity of the magnetron-sputtered Ru–Ir alloy electrodes in acidic media follows the Ru content, suggesting that the initial activity of the alloy-derived catalysts is governed mainly by Ru-rich oxide-like phases. Independent contributions of the alloy components to the overall catalytic activity are also reflected in the operando spectroscopic data. In-situ O K edge spectroscopy indicates the OER activity of alloy-derived catalysts to be initially confined to Ru in an oxide-like moiety conforming to a cus arrangement encountered in rutile-type RuO2. The presence of Ir in the catalyst decreases the ability of the electrode material to stabilize hydrous oxide-like environments at the surface. This behavior is attributed to a less hydrophilic character of the Ir-containing surface oxides. Element-specific operando XPS confirms Ru to be the preferentially oxidized catalyst component, forming highly oxidized RuOx-like species. The Ir, on the other hand, changes its oxidation state to a much lower extent. The spectroscopic data conform to a model in which Ru–Ir alloys, upon activation, do not form a synergistic mixed Ru–Ir oxide phase but evolve into composition-dependent oxide-like domains.