Stable tetravalent Ni species generated by reconstruction of FeB-wrapped NiMoO pre-catalysts enable efficient water oxidation at large current densities

High valence transition metals offer highly active electrocatalytic sites for oxygen evolution reaction (OER) but suffer from high formation energy and are thermodynamically unstable in the resting state. Herein, we report the generation of NiFeOOH with highly oxidized and stable tetravalent Ni species through reconstruction and electronic structure modulation. The resulted NiFeOOH electrocatalyst catalyzes OER with ultralow overpotentials of 166 and 213 mV at 10 and 100 mA cm-2, respectively, and high stability (> 100 h) at an ultrahigh current density of 1000 mA cm-2. The formation of stable tetravalent Ni species in NiFeOOH nanosheets/rods structure results in higher Ni-O covalency and enhanced the reactivity of lattice oxygen, thus transferring the reaction path and reducing the reaction energy barrier for OER. This work paves the way for the rational design of electrocatalysts with high-valence metal species and activated lattice oxygen for stable water oxidation at large current densities.