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

摘要

Amorphous and monoclinic wolframite NiWO4 nanoparticles are successfully synthesized by annealing the NiWO(4-)70 sample obtained via the simple chemical precipitation approach at 300 and 600 degrees 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 similar to 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.