Tailoring hypervalent Nickel induced by oxygen vacancy toward enhanced oxygen evolution reaction performance in self-supporting NiFe-(oxy)hydroxides electrodes.

NiFe-(oxy)hydroxides are the most active transition metal oxide electrocatalysts for oxygen evolution reaction (OER) under the alkaline media. Herein, we controllably manipulated oxygen vacancy (V)-tunable NiFe-(oxy) hydroxides that their OER performances possessed a volcano-type relationship with V concentration, positively-correlated with Ni/Ni ratio. Theoretical simulations further unearthed the enhanced activation and dissociation of HO by the inserting of V. As a result, the optimal sample featuring the Ni/Ni ratio of 30.3 % and V of 23.8 % exhibited the overpotential of 243 mV at the current density of 100 mA cm, simultaneously lasting 120 h durability without any attenuation, exceding the most reported NiFe-(oxy)hydroxides. This work offers an innovative view to understand the OER performance using hypervalent Ni ratio induced by V defects.