Ternary Iron(III)-Antimony(V) Oxide Thin Films as Protective Layers for Ruthenium(IV) Oxide as Anode Electrocatalysts for Acidic Water Splitting

Abstract An efficient use of noble metals is key to achieving sustainable hydrogen production via water electrolysis. Here, we extended the lifetime of RuO2 anode electrodes by protecting them with a thin film of Fe(III)–Sb(V) oxide. The protective oxide film is produced via spray pyrolysis and consists of FeSbO4 with similar lattice parameters and a space group as RuO2. Both RuO2 and FeSbO4 are produced under the same synthesis conditions, a desired characteristic for continuous and scalable production technologies. We identify that the growth temperature clearly affects the chemical composition and crystallinity of the Fe(III)–Sb(V) oxide films, yielding high-purity and crystalline FeSbO4 at 500 °C. Electrochemical studies revealed that crystalline FeSbO4 electrodes exhibit improved stability when cycled at potentials as high as 2 V vs RHE, while the amorphous Fe–Sb compound produced at lower temperatures gradually dissolves during the cyclic voltammetry experiments. Conductive atomic force microscopy and cyclic voltammetry reveal quasi-metallic behavior, likely arising from a high density of surface states and preferential electron transport pathways. Chronopotentiometry measurements (10 mA cm–2) confirm the positive effect of the protective layer, showing an increase in the lifetime of the electrode from ∼20 to ∼60 h for the best-performing electrodes. This opens a pathway to use metal antimonates as protective coatings for electrocatalysts that are susceptible to corrosion during anodic and acidic conditions seen in the oxygen evolution reaction.