An urchin-like Co-doped NiS2/C nanorod array with enriched sulfur vacancies for asymmetric supercapacitors

The electrochemical activity and stability of transition metal sulfides are severely restricted by their poor conductivity and charging-discharge deformation. In this work, trimesic acid (H3BTC) was used as an organic ligand for the coprecipitation reaction, and a 3D urchin-like Co-NiBTC nanorod array was selected as the precursor for the synthesis of Co-NiO, Co-NiS2 and Co-NiS2/C. Experimental investigation and theoretical analysis suggest that Co-NiS2/C possesses a stable urchin-like morphology inherited from the precursor, enriched sulfur vacancies and porosity due to the one-step pyrolysis, increased density of free electrons due to Co-doping, and enhanced electron transmission from the carbon matrix. Compared to Co-NiO and Co-NiS2, Co-NiS2/C exhibits a larger capacitance of 1080 F g(-1) at 1 A g(-1), longer cycle life (89.2% at 3 A g(-1) after 8000 cycles) and higher rate capability. Furthermore, the asymmetric supercapacitor device of Co-NiS2/C//AC exhibits an energy density of 36 W h kg(-1) at a power density of 1271.5 W kg(-1). The excellent electrochemical performance can be attributed to its relatively high surface area conducive to the exposure of electrochemically active sites, the porous structure that promotes ion transportation, and the carbon skeleton binding that improves the electrical conductivity. It is of great significance for vacancy introduction pathways and design principles of various MOF-derived metal compound materials used in electrochemical energy storage.