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

Surface engineering can disruptively raise the intrinsic performance of electrocatalytic materials. Herein, we propose a facile surface nitridation stretgy for nickel-cobalt alloy (NiCo-N) nanocactoids grown on carbon cloth in substantially raising the oxygen evolution reaction (OER) kinetics. Indeed, NiCo-N exhibits an ultralow OER overpotential of 214 mV at 10 mA cm in alkaline media, together with a small Tafel slope of 53 mV dec, 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 NiCo-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 NiCo alloy precatalyst, peroxo O 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.