Morphological and electronic modification of NiS2 for efficient supercapacitors and hydrogen evolution reaction

Rational design of highly active and low-cost electrode material toward energy storage and hydrogen evolution reaction (HER) is promising but still challenging. Herein, we present V-doped pyrite NiS2 nanosheets grown on carbon cloth (VNS/CC) as an efficient electrode material for supercapacitors and HER. The optimal 20% VNS/CC electrode exhibited ultra-high specific capacity (1970 F g  1 at 1 A g  1) with excellent long-term cycling stability (100% retention over 6000 cycles). The 20% VNS/CC//AC battery-supercapacitor hybrid device presented high-energy and high-power performances (e.g., 64.4 W h kg  1 at 799 W kg  1) and excellent cycling stability. Furthermore, the 20% VNS/CC exhibited superior HER performance, including low overpotential and exceptional stability. The combined experiments and density functional theory (DFT) calculations revealed that the superior supercapacitor and HER performance of VNS/CC are attributed to the doping of V on the NiS2 surface/subsurface: (i) significant modulation of the morphology to promote the formation of independent nanosheet structures with abundant active sites and induced pseudocapacitance effects; (ii) practical tuning of the NiS2 electronic structure to convert the semiconductor characteristics into metallic properties with high conductivity, and (iii) optimize the adsorption/dissociation energy of water molecules to enhance the Volmer step reaction rate in alkaline solutions.