When NiO@Ni Meets WS<sub>2</sub> Nanosheet Array: A Highly Efficient and Ultrastable Electrocatalyst for Overall Water Splitting

The development of low-cost, high-efficiency, and stable bifunctional electrocatalysts toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance for large-scale water splitting. Here, we develop a new strategy for the first design and synthesis of a NiO@Ni decorated WS<sub>2</sub> nanosheet array on carbon cloth (NiO@Ni/WS<sub>2</sub>/CC) composite. This composite serves as a unique three-dimensional (3D) synergistic electrocatalyst that not only combines the intrinsic properties of individual NiO@Ni and WS<sub>2</sub>, but also exhibits significantly improved HER and OER activities when compared to that of pure NiO@Ni and WS<sub>2</sub>. This electrocatalyst possesses Pt-like activity for HER and exhibits better OER performance than that for commercial RuO<sub>2</sub>, as well as demonstrating superior long-term durability in alkaline media. Furthermore, it enables an alkaline electrolyzer with a current density of 10 mA cm<sup>–2</sup> at a cell voltage as 1.42 V, which is the lowest one among all reported values to date. The excellent performance is mainly attributed to the unique 3D configuration and multicomponent synergies among NiO, Ni, and WS<sub>2</sub>. Our findings provide a new idea to design advanced bifunctional catalysts for water splitting.