Fe2O3/P-doped CoMoO4 electrocatalyst delivers efficient overall water splitting in alkaline media

Phosphorization of molybdates has been shown to promote hydrogen evolution reaction (HER) activity but is usually detrimental to oxygen evolution reaction (OER) activity, frustrating efforts to create bifunctional HER/OER electrocatalysts. Herein, we show that Fe₂O₃-modulated P-doped CoMoO₄ on nickel foam (Fe-P-CMO) is an excellent bifunctional HER/OER electrocatalyst in alkaline media, with the adverse effect of phosphorization on the OER activity of CoMoO₄ being countered via Fe₂O₃ introduction. An alkaline splitting electrolyser assembled directly using the self-supporting Fe-P-CMO electrode possessed outstanding long-term durability with ultralow cell voltages of 1.48 and 1.59 V required to achieve current densities of 10 and 100 mA cm⁻², respectively. Detailed experimental investigations showed that during HER, P-doped CoMoO₄ in Fe-P-CMO underwent surface reconstruction with the in-situ formation of Co(OH)₂ on the P-CoMoO₄ (Co(OH)₂/P-CoMoO₄). During OER, P-doped CoMoO₄ was deeply reconstructed to CoOOH with the complete dissolution of Mo, leading to the in-situ formation of Fe₂O₃/CoOOH heterojunctions.