Highly Efficient NiS/Ni(OH) Heterogeneous Structure Electrocatalyst with Regenerative Oxygen Vacancies for Oxygen Evolution Reaction.

Developing low-cost and highly efficient electrocatalysts toward oxygen evolution reaction (OER) is of vital significance for electrochemical water splitting. Herein, we fabricate a heterostructure NiS/Ni(OH) electrocatalyst (Ni-S-n) with regenerative oxygen vacancies via electro-deposition on nickel foam (NF) followed by a facile NaBH reduction. The resulting Ni-S-5 catalyst with appropriate amount of oxygen vacancies (O) exhibits extraordinary activity for alkaline OER with overpotential of 142 mV and 248 mV to reach the current density of 10 mA cm and 100 mA cm, respectively. This catalyst also shows remarkable durability with 40 h. After the stability test, the excellent OER performance is well recovered by regenerating the surface oxygen vacancies (O) significantly with additional NaBH reduction. The Ni-S-5 catalyst still displays good activity even after repeating it three times (180 h). The surface oxygen vacancies act as vital active sites for OER. A mechanism of O species transformation and regeneration based on the Ni-S-5 catalyst is proposed, which provides a new direction for exploring ultrastable and efficient OER electrocatalysts with renewable active species.