Improved electrocatalytic performance with enlarged surface area and reduced bandgap of caterpillar and cabbage-like nickel sulphide nanostructures

Abstract

In the present work, two different phases of nickel sulphide (β-NiS and NiS2) were successfully synthesized via facile hydrothermal route. The physical and chemical characterizations such as X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirms formation of β-NiS and NiS2. Mesoporous caterpillar and cabbage-like nanostructures were observed in FESEM image with enlarged specific area 247.22 m2/g and 251.47 m2/g, respectively. Due to large surface area of the synthesized β-NiS and NiS2 nanoparticles, bandgap was found to be reduced as 0.98 eV and 0.74 eV, respectively, than the bulk NiS. Charge transfer characteristics were examined by electrochemical impedance spectroscopy (EIS) technique; caterpillar-like nanostructures (β-NiS) has lowest charge transfer resistance 2.91 Ω, due to its unique structure. Cyclic Voltammetry (CV) analysis reveals that the synthesized β-NiS and NiS2 nanoparticles show that the charge storage mechanism is non-Faradaic. Cabbage-like β-NiS nanoparticles show maximum areal capacitance 14.24 F cm−2 in 1 M LiOH electrolyte and show 89% cyclic stability over 1000 cycles. The electrocatalytic performance, such as high areal capacitance and lower charge transfer resistance indicate that the synthesized β-NiS and NiS2 nanoparticles facilitate fast ion diffusion during redox processes.