Surface nitridation of nickel-cobalt alloy nanocactoids raises the performance of water oxidation and splitting

[Display omitted] •Surface nitridation tailoring of cactoid nickel-cobalt alloy (Ni2Co-N) was proposed.•Surface nitridation regulates the adsorption of oxygen intermediates on Ni2Co-N.•Fast surface reconstruction of Ni2Co-N enables the mass production of active sites.•Ni2Co-N exhibits an ultralow OER overpotential of 214 mV at 10 mA cm–2.•In situ produced peroxo-like O22− species activate advanced LOM mechamism. Surface engineering can disruptively raise the intrinsic performance of electrocatalytic materials. Herein, we propose a facile surface nitridation stretgy for nickel-cobalt alloy (Ni2Co-N) nanocactoids grown on carbon cloth in substantially raising the oxygen evolution reaction (OER) kinetics. Indeed, Ni2Co-N exhibits an ultralow OER overpotential of 214 mV at 10 mA cm–2 in alkaline media, together with a small Tafel slope of 53 mV dec−1, which not only breaks the cap of theoretical overpotential limit, but also is remarkably lower than those of the state-of-the-art 3d transition metal alloys and their derivatives. A nearly 100 % Faraday efficiency with a low and stable cell voltage of 1.59 V is achieved by an alkaline water electrolyzer made of the bifunctional Ni2Co-N as both the anode and cathode catalysts. The chemical and structural origin of the high catalytic activity is established to root from the fast surface reconstruction of Ni2Co alloy precatalyst, peroxo O22- species-induced lattice oxygen oxidation mechanism, acceleration in electron transfer, as well as the large active surface area as a result of the surface nitridation. The present study provides a guideline to rationally design active and stable 3d transition metal catalysts towards water oxidation and splitting.