Synthesis of nickel chalcogenide hollow spheres using an l-cysteine-assisted hydrothermal process for efficient supercapacitor electrodes

Abstract

Transition metal materials, NiS, NiO and NiSe₂, with a uniform hollow-structure were obtained based on NiS₂ hollow spheres, and were successfully synthesized with an L-cysteine assisted hydrothermal method at 120 °C. The electrochemical properties of the NiS₂, NiS, NiO and NiSe₂ hollow sphere electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy tests. Firstly, the cyclic voltammetry curves of the four materials all displayed pseudo-capacitance behaviour. Moreover, the galvanostatic charge–discharge tests showed that the specific capacitance of the NiS₂, NiS, NiO and NiSe₂ electrodes was 1643 F g⁻¹, 1076 F g⁻¹, 581 F g⁻¹ and 341 F g⁻¹, respectively, at a current density of 1 A g⁻¹. After 1000 cycles, the specific capacitance of the NiS₂, NiS, NiO and NiSe₂ electrodes was retained at 455 F g⁻¹, 368 F g⁻¹, 246 F g⁻¹ and 269 F g⁻¹, respectively. The results implied that both the NiS₂ and NiS electrodes exhibited higher specific capacitance, while the NiO and NiSe₂ electrodes showed a longer cycling life. This work highlights the advantageous electrochemical performance of the different nickel compounds, and contributes to providing a good reference for the preparation of superior supercapacitor materials with high performance.