Influence of Catalyst Composition on the Acidic Oxygen Evolution Reaction: From Single Oxide IrO2 to High-Entropy Oxide IrNiMnFeCoCuVOx

Developing active and robust catalysts for the acidic oxygen evolution reaction (OER) with reduced Ir loading is still a challenge in the industrial production of green H2. In this work, several catalysts ranging from single metal oxides (e.g., IrO2) to high-entropy oxides (IrNiMnFeCoCuVOx) were synthesised through thermal decomposition in air to study the effect of the mixed-oxide composition in terms of activity and stability towards the acidic OER. Catalysts were named MOx-n, with n being the number of metal elements in the mixture. The results show that the activity of rutile IrO2 can be improved by introducing other elements into the composition. The best performance was obtained for MOx-4 to MOx-5, which delivered a current density of 10 mA cm−2 at an overpotential (η10) of 279 ± 4 mV; approx. 100 mV lower than IrO2 at a comparable Ir loading and with better stability. Nevertheless, further increasing the complexity of the mixed oxide resulted in an evident degradation in terms of activity and stability. It is worth noting that surface dissolution and reconstruction occurred with all mixed-oxide catalysts, including high-entropy configurations.