Structural and bandgap tuning of self-supported Zn–NiS thin nano-sheets as efficient supercapacitor electrode material

Abstract

Doping based induced defects and morphology tuning in nickel sulfide plays a crucial role for performance improvement and stability. So, in pursuit of high-performance supercapacitors, the morphology and conductivity of nickel sulfide (NiS) nano-sheets have been tailored through strategic doping with transition metal zinc (Zn). The Zn incorporation in NiS induced structural and electrochemical changes with varying doping concentrations of 1 %, 3 % and 5 % (total weight of host material) named as NiZn₁S, NiZn₃S and NiZn₅S respectively. The morphological, chemical, structural, compositional and optical results of SEM, TEM, HRTEM, EDS, XRD, FTIR, PL and UV revealed NiZn₃S to be the best as its nano-sheets like morphology has offered high active surface area which ultimately increases the electrochemical performance as well as stability. The supreme specific capacitance of NiZn₃S recorded 1322 Fg^_1 at 1 Ag^_1 with splendid cyclic retention of 94 % after 5000th cycles. NiZn₃S exhibited both charge storage mechanisms with 29 % capacitive controlled and 71 % diffusive controlled contribution ratio at 5 mVs^_1. The power law (b = 0.67) and pseudocapacitive behavior dominated by observing increased trend in capacitive (surface) contribution ratio with increased scan rate proves its suitability for supercapacitors.