Nanocrystalline cobalt boride (Co-B) thin films prepared by pulsed laser deposition were used as an anode catalyst to study the water oxidation reaction in alkaline medium. Elemental depth profiling revealed the bulk of the film to be metallic, which helps in improving conduction of charges, while the surface of the film was rich in CoOOH-type species to facilitate the oxygen evolution reaction (OER). Comparison of OER performance with boron-free samples suggests that inclusion of B helps in improving the OER rate by preventing the conversion of surface Co to stable oxides. The Co-B film achieved a current density of 10 mA/cm2 at merely 280 mV, with potentiostatic stability for 45 h in alkaline medium, highlighting its superior performance than the powder catalyst. This work not only establishes the advantage of developing thin-film catalysts but also presents a new approach to understand the OER mechanism in metal borides.

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