Ni(OH)2 Templated Synthesis of Ultrathin Ni3S2 Nanosheets as Bifunctional Electrocatalyst for Overall Water Splitting

Ultrathin nickel (Ni)‐based sulfide nanosheets have been reported as excellent electrocatalysts for overall water splitting; however, the uncontrollability over thickness due to the nonlayered structure still hampers its practical application. Herein, a simple topochemical conversion strategy is employed to synthesize cobalt‐doped Ni3S2 (Co‐Ni3S2) ultrathin nanosheets on Ni foam. The Co‐Ni3S2 nanosheets are controlled synthesized by using Co‐Ni(OH)2 ultrathin nanosheets as templates with anneal and sulfurization treatment, showing exceptional electrocatalytic activity. This template‐assisted method can also be applied to obtain Ni, NiO, and NiPx nanosheets, providing a universal strategy to synthesize ultrathin nanosheets of nonlayered materials. The overall water splitting of this Co‐Ni3S2 ultrathin nanosheets achieves a low voltage of 1.54 V at a current density of 10 mA cm−2 and high durability in 1 m KOH, comparable to the best performance of electrochemical water splitting ever reported. The detailed structural transformation of Ni‐based sulfides in the catalytic process and its mechanism are further explored both experimentally and theoretically. Ultrathin Ni3S2 nanosheets are synthesized by a simple topochemical conversion method by using atomically thin Ni(OH)2 as template, exhibiting extraordinary performance as electrocatalyst for overall water splitting. This template‐assisted method can also be utilized to synthesize Ni, NiO, and NiPx ultrathin nanosheets, promising for different applications. The rational design is instructive to the exploitation of other electrocatalysts.