Contemporaneous inverse manipulation of the valence configuration to preferred Co2+ and Ni3+ for enhanced overall water electrocatalysis

Abstract Valence configurations of active sites are essential for modulating the electronic structure of the non-noble metal electrocatalysts in water splitting. However, synchronously engineering the valence states of different elements to inverse ones has been a key challenge in the integrated synthesis environment. Herein, for the first time, a novel superstructure of inverse spinel NiCoFe oxide nanocubes with contemporaneous valence regulation to preferred Co2+ and Ni3+ (NiIIICoIIFe-O@NF, NF stands for nickel foam), has been developed by in situ topotactic chemical transformation. NiIIICoIIFe-O@NF can attain a current density of 10 mA cm−2 at a low cell voltage of 1.455 V in 1 M KOH when used as bifunctional catalysts. Density functional theory calculations suggested that the favorable Co2+ and Ni3+ act synergistically to lower down ΔGH* for HER and the OER overpotential in an optimal pathway. Our study probes the construction and understanding of the heterogeneous valence configuration in a single phase.