Hierarchically Structured Bifunctional Electrocatalysts of Stacked Core-Shell CoS1-xPx Heterostructure Nanosheets for Overall Water Splitting

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 RuO2||Pt/C couple (1.6 V).