Mixed Metal-Antimony Oxide Nanocomposites: Low pH Water Oxidation Electrocatalysts with Outstanding Durability at Ambient and Elevated Temperatures

Electrochemical water splitting with a proton-exchange membrane electrolyte provides many advantages for the energy-efficient production of high-purity H₂ in a sustainable manner, but the current technology relies on high loadings of expensive and scarce iridium at the anodes, which are also often unstable in operation. To address this, the present work scrutinises the electrocatalytic properties of a range of mixed antimony-metal (Co, Mn, Ni, Fe, Ru) oxides synthesised as thin films by a simple solution-based method for the oxygen evolution reaction in aqueous 0.5 M H₂SO₄. Among the noble-metal free catalysts, cobalt-antimony and manganese-antimony oxides demonstrate good stability over 24 h and reasonable activity at 24 ± 2 °C, but slowly lose their initial activity at elevated temperatures. The ruthenium-antimony system is highly active, requiring an overpotential of only 0.39 ± 0.03 and 0.34 ± 0.01 V to achieve 10 mA cm^-2 at 24 ± 2 and 80 °C, respectively, and most importantly, remaining remarkably stable during one-week tests at 80 °C. Detailed characterisation reveals that the enhanced stability of metal-antimony oxides water oxidation catalysts can arise from two distinct structural scenarios: either formation of a new antimonate phase, or nanoscale intermixing of metal and antimony oxide crystallites. Density functional theory analysis further indicates that the stability in operation is supported by the enhanced hybridisation of the oxygen p- and metal d-orbitals induced by the presence of Sb.