Hierarchical Nickel Sulfide Nanosheets Directly Grown on Ni Foam: A Stable and Efficient Electrocatalyst for Water Reduction and Oxidation in Alkaline Medium

Developing high-performance nonprecious electrocatalysts for water reduction and oxidation is highly desirable for future energy supplement. Herein, a facile one-pot strategy is reported to obtain Ni3S4 nanosheets directly grown on Ni foam (NiS/NF) as bifunctional nonprecious electrocatalyst toward full water splitting through a facile hydrothermal-sulfurization method in Na2S solution. The resultant unique structure with integrated hierarchical three-dimensional (3D) configuration can enhance mass transport and charge mobility and facilitate the diffusion of generated gases (H2 and O2). Thus, the prepared NiS/NF exhibits remarkable catalytic activity and outstanding stability for water oxidation and reduction reaction in alkaline electrolyte. For hydrogen evolution reaction (HER), it only needs a low overpotential of −122 mV to render a current density of 10 mA cm–2 with a small Tafel slope of 69 mV dec–1, whereas it delivers a current density of 20 mA cm–2 for oxygen evolution reaction (OER) at the overpotential of 320 mV together with Tafel slope of 71 mV dec–1. Importantly, when NiS/NF is assembled as an alkaline electrolyzor, it only needs a cell voltage of 1.61 V to provide current density of 10 mA cm–2 and maintains this current density for over 20 h with a recession of 4.5%. Various characterizations and controlled experiments reveal that the outstanding activity and robust stability of NiS/NF for electrocatatlytic water splitting are attributed to its integrated electrode configurations of the electrochemically active constituents and the conductive Ni foam and unique superstructure with high electrochemical surface area.