Summary
Designing highly efficient electrode materials is one of the key issues for developing high performance energy storage devices and electrolytic hydrogen production. Herein, binder-free core-shell CoSx@CoNi2S4/CC nanocomposites were successfully prepared via calcination-sulfurization-electrodeposition using in-situ grown ZIF-67 nanorods as the precursor and self-sacrificial template. Attributed to the excellent electrical conductivity of the metal polysulfides core and CoNi2S4 shell and the unique nanosheet/nanoflower morphology with multidimensional interfaces providing rich active centers and fast transport paths, the synthesized CoSx@CoNi2S4/ CC not only presented excellent energy storage performance, but also delivered good activity toward hydrogen evolution reaction. The optimal CoSx@CoNi2S4-20/CC exhibited high capacities of 985 Cg-1 (i.e., 328.3 mA h g-1; capacitance of 1970 F g- 1) at 1 A g-1 and excellent rate performance (92% capacity retention at 10 A g-1). Density-functional theory calculations reveal that the metal polysulfides presented great OH adsorption ability. The assembled CoSx@CoNi2S4/CC//AC hybrid supercapacitor and CoSx@CoNi2S4/CC//Fe supercapacitor-type battery showed high energy density (50 Wh kg-1 at 799 W kg-1 and 53.3 Wh kg-1 at 800 W kg-1) and cycle stability (about 81% of the initial specific capacity at 10 A g-1 after 6000 cycles).