Effect of synthetic methods on electrochemical performances of VOPO4·2H2O supercapacitor

In this paper, we studied the VOPO 4 ·2H 2 O as an electrode material for supercapacitors. A systematic comparison of VOPO 4 ·2H 2 O prepared by reflux and hydrothermal methods was carried out through detailed analyses that included power X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Their electrochemical performances were also investigated by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Meanwhile, we proposed a possible charge storage mechanism on the VOPO 4 ·2H 2 O electrode surface. The material synthesized by reflux method had better performance in the capacitance than that by hydrothermal method, and its specific capacitance was up to 202 F/g at 2 mV/s. A total of 67.4 % of capacitance was maintained for the VOPO 4 ·2H 2 O synthesized by reflux method when current density changed from 0.2 to 2 A/g, much higher than those obtained from the hydrothermal-synthesized VOPO 4 ·2H 2 O supercapacitor of 42.5 %. The energy density of VOPO 4 ·2H 2 O supercapacitor synthesized by reflux method was 18.7 Wh/kg at 290 W/kg and maintained 6.2 Wh/kg at 1,421 W/kg, much higher than the hydrothermal-synthesized VOPO 4 ·2H 2 O supercapacitor. Our work confirms that VOPO 4 ·2H 2 O is a potential electrode material for supercapacitors.