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 O )-tunable NiFe-(oxy) hydroxides that their OER performances possessed a volcano-type relationship with V O concentration, positively-correlated with Ni 3+ /Ni 2+ ratio. Theoretical simulations further unearthed the enhanced activation and dissociation of H 2 O by the inserting of V O . As a result, the optimal sample featuring the Ni 3+ /Ni 2+ ratio of 30.3 % and V O of 23.8 % exhibited the overpotential of 243 mV at the current density of 100 mA cm –2 , 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 O defects.