High-valence metals improve oxygen evolution reaction performance by modulating 3d metal oxidation cycle energetics

Multimetal oxyhydroxides have recently been reported that outperform noble metal catalysts for oxygen evolution reaction (OER). In such 3d-metal-based catalysts, the oxidation cycle of 3d metals has been posited to act as the OER thermodynamic-limiting process; however, further tuning of its energetics is challenging due to similarities among the electronic structures of neighbouring 3d metal modulators. Here we report a strategy to reprogram the Fe, Co and Ni oxidation cycles by incorporating high-valence transition-metal modulators X (X = W, Mo, Nb, Ta, Re and MoW). We use in situ and ex situ soft and hard X-ray absorption spectroscopies to characterize the oxidation transition in modulated NiFeX and FeCoX oxyhydroxide catalysts, and conclude that the lower OER overpotential is facilitated by the readier oxidation transition of 3d metals enabled by high-valence modulators. We report an ~17-fold mass activity enhancement compared with that for the OER catalysts widely employed in industrial water-splitting electrolysers. Multimetal oxyhydroxides are among the most active catalysts for alkaline water oxidation, but tuning their properties remains a challenge. Now, the performance of NiFe- and FeCo-based catalysts is optimized with the incorporation of high-valence modulator metals, which shifts the active metals towards lower valence states and enables lower overpotentials.