Probing the effect of metal to ligand charge transfer on the oxygen evolution reaction in Au incorporated Co(OH)₂ thin film electrocatalysts

First row transition metal oxides have shown potential as affordable catalysts for the oxygen evolution reaction (OER). The addition of small amounts of noble metals such as gold offers significant improvements in catalytic activity while maintaining affordability. However, a fundamental understanding of this enhancement in catalytic activity is still lacking. In this work we correlate Near Edge X-ray Absorption Fine Structure (NEXAFS) data to conventional characterisation techniques to analyse the oxidation state changes that occur during the OER in cobalt oxide and cobalt oxide-gold based electrocatalyst thin films to understand their effect on the reaction. We find that the incorporation of gold into the cobalt oxide significantly reduces the ligand to metal charge transfer process on the catalyst surface. We propose that the reduced ligand to metal charge transfer facilitates the formation of the key M-OOH* intermediate (where M is the metal and -OOH* is the ligand) and desorption of O2 from the catalyst surface, leading to an overall increase in catalyst performance. This study sheds light on how incorporation of a small amount of highly electronegative noble metal may have the scope to significantly improve the reactivity of transition metal based thin film catalysts for OER by optimising the ligand to metal charge transfer effect.