Non-stoichiometric NiOx nanocrystals for highly efficient electrocatalytic oxygen evolution reaction

Abstract Designing a low–cost, large–scale and highly–active electrolytic oxygen evolution catalyst is still a huge challenge. Pure stoichiometric NiO is inevitably an insulator, which hampers the electron transfer and transport in catalysis. While non-stoichiometric NiOx is a wide bandgap p-type semiconductor. The conductive interface of non-stoichiometric NiOx NCs is successfully fabricated, which the p-type conductivity of NiOx originates from two positive charge compensation which favored Ni2+ vacancies. The valence band (VB) of NiOx is well adjustable so that the strong electron interaction induces electronic structure modulation, which optimizes the binding energy of *OOH intermediates. In the alkaline water splitting, non-stoichiometric NiOx NCs exhibit remarkable performance toward OER with an overpotential of 330 mV (1.56 V vs. RHE) at 10 mA cm−2 and a Tafel slope of 105.17 mV dec−1, as well as an extraordinary robust stability. Detailed investigations show that the high density of defects combine with oxygen atoms to form NiOOH species, which are conducive to the OER kinetics. This work offers valuable generalized insights for constructing robust non-stoichiometric metal oxides electrocatalysts and encouraging for large-scale practical applications.