Hierarchically Structured Bifunctional Electrocatalysts of Stacked Core–Shell CoS₁₋<i>_x</i>P<i>_x</i> Heterostructure Nanosheets for Overall Water Splitting

Abstract

Abstract The rational design and strategy of obtaining stable bifunctional electrocatalysts with unique functionalities are prerequisite to achieving robust catalytic activity. In this study, a composition‐controlled partial sulfurization/phosphorization strategy to synthesize a doughnut‐like 3D heterostructured electrocatalyst for overall water splitting is proposed, wherein core–shell 2D CoS 1− x P x nanosheets decorated with N‐doped carbon are self‐assembled to form a hierarchical 3D architecture. The composition and phase structure in core–shell CoS 1− x P x can be readily modified by controlling the liquid phase sulfurization and subsequent phosphorization, thereby modifying the electronic structure and activating the intrinsic active sites. The resulting CoS 1− x P x benefits from the unique structural features including high accessible active surface area, adequate amount of reactive sites, intimate interfacial coupling between the components, interconnected electron highway, and accelerated charge/mass transfer ability. Consequently, the optimized CoS 0.46 P 0.54 electrocatalyst achieves a catalytic current density of 10 mA cm −2 at overpotentials as low as 101 and 302 mV for hydrogen evolution reaction and oxygen evolution reaction, respectively, with outstanding long‐term operational stability in alkaline solution. The CoS 0.46 P 0.54 couple enables an alkaline water electrolysis with a current density of 10 mA cm −2 at a low cell voltage of 1.62 V, comparable to that of the RuO 2 ||Pt/C couple (1.6 V).