Proton-exchange membrane water electrolysers
provide many advantages for the energy-efficient production of H<sub>2</sub>,
but the current technology relies on high loadings of expensive iridium at the
anodes, which are often unstable in operation. To address this, the present
work scrutinises the properties of antimony-metal (Co, Mn, Ni, Fe, Ru) oxides
synthesised as flat thin films by a solution-based method for the oxygen
evolution reaction in 0.5 M H<sub>2</sub>SO<sub>4</sub>. Among the non-noble-metal
catalysts, only cobalt-antimony and manganese-antimony oxides demonstrate high
stability and reasonable activity under ambient conditions, but slowly lose
activity at elevated temperatures. The ruthenium-antimony system is highly
active, requiring an overpotential of 0.39 ± 0.03 and 0.34 ± 0.01 V to achieve
10 mA cm<sup>-2</sup> at 24 ± 2 and 80 °C, respectively, and remaining
remarkably stable during one-week tests at 80 °C. The <i>S</i>-number for this catalyst is higher than that for the high-performance
benchmark Ir-based systems. Density functional theory analysis and physical
characterisation reveal that this high stability is supported by the enhanced
hybridisation of the oxygen p- and metal d-orbitals induced by antimony, and
can arise from two distinct structural scenarios: either formation of an
antimonate phase, or nanoscale intermixing of metal and antimony oxide
crystallites.
Mixed Metal-Antimony Oxide Nanocomposites: Low pH Water Oxidation Electrocatalysts with Outstanding Durability at Ambient and Elevated Temperatures