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

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)_x electrocatalyst (Ni-S-n) with regenerative oxygen vacancies via electro-deposition on nickel foam (NF) followed by a facile NaBH₄ reduction. The resulting Ni-S-5 catalyst with appropriate amount of oxygen vacancies (O_vs) exhibits extraordinary activity for alkaline OER with overpotential of 142 mV and 248 mV to reach the current density of 10 mA cm^-2 and 100 mA cm^-2, 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_vs) significantly with additional NaBH₄ 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_vs 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.