Amorphous NiWO4 Nanospheres with High-Conductivity and -Capacitive Performance for Supercapacitors

Amorphous and monoclinic wolframite NiWO4 nanoparticles are successfully synthesized by annealing the NiWO4_70 sample obtained via the simple chemical precipitation approach at 300 and 600 °C, respectively. With the elevated annealing temperature, the specific surface area reduces appreciably with decreasing porosity. The electrical conductivity of amorphous NiWO4_300 sample enhances almost 1 order of magnitude than that of crystal NiWO4_600 sample. The electrochemical properties of NiWO4_x (x = 300 and 600) as electrodes of supercapacitors are characterized via the potentiostatic and galvanostatic cycle measurements and electrochemical impedance spectroscopy (EIS). The NiWO4_300 electrode exhibits an excellent specific capacitance of 437.2 F g–1 at a current density of 0.1 A g–1 and ∼54% capacitive retention while the current density is enhanced 10-fold. Meantime, the NiWO4_300 electrode displays the high Coulombic efficiency (>94%) after 500 cycles. The excellent electrochemical performance of the amorphous NiWO4_300 electrode could result from the diffusion-controlled kinetics, high electrical conductivity, and large surface area.