Comparative study of the electrochemical properties of mesoporous 1-D and 3-D nano- structured rhombohedral nickel sulfide in alkaline electrolytes

Mesoporous beta-NiS (nickel sulfide) has been synthesized by a hydrothermal route using thiourea as a sulfur source. FESEM and TEM images confirm the formation of one dimension (1-D) or three dimension (3-D) nanostructures. 1-D or 3-D nanostructures were formed by varying the concentration of thiourea. The growth mechanisms for formation of 1-D and 3-D nano-structures have been studied in detail. No other phases of nickel sulfide were detected in the XRD and XPS spectra. Comparative studies of the electrochemical behaviour of the synthesized beta-NiS have been performed in various alkaline electrolytes (KOH, LiOH, and NaOH). beta-NiS showed superior electrochemical performance in aqueous LiOH electrolyte than aqueous KOH and NaOH electro lye. 1-D growth of beta-NiS nano-rods showed to a maximum areal capacitance of 3.66 F cm(-2) and excellent cyclic stability of 88% over 1000 cycles in aqueous LiOH electrolyte. The1-D growth provides effective pathways for ion diffusion and improve the electron-transfer rate, promoting faradaic reaction in the charge-storage process. Impedance parameters were calculated from Nyquist plot, where beta-NiS1-D nano-rods showed the lowest charge-transfer resistance of 1.29 Omega and a high Warburg impedance of 398.94 Omega.s(-1/2). The measured parameter of the synthesized beta-NiS nanostructures indicates that these are the promising electrode material for electrochemical devices.