The effect of calcination temperature on the capacitive properties of WO3-based electrochemical capacitors synthesized via a sol-gel method

Electrochemical capacitor (EC) is a promising energy storage device which can be hybridized with other energy conversion or energy storage devices. One type of ECs is pseudocapacitor made of metal oxides. WO3 is an inexpensive semiconductor metal oxide which has many applications. However the application of WO3 as an EC material was rarely reported. Therefore in this research EC was prepared from WO3 nanomaterial synthesized by a sol-gel process. The WO3 gel was spin-coated on graphite substrates and calcined at various temperatures of 300 degrees C, 400 degrees C, 500 degrees C and 600 degrees C for 1 h. Cyclic voltammetry (CV) measurements were used to observe the capacitive property of the WO3 samples. SEM, XRD, FTIR and Brunauer-Emmett-Teller (BET) analyses were used to characterize the material structures. WO3 calcined at 400 degrees C was proved to have the highest capacitance of 233.63 F.g(-1) (1869 mF.cm(-2)) at a scan rate of 2 mV.s(-1) in 1 mol/L H2SO4 between potentials -0.4 and 0.4 V vs. SCE. Moreover it also showed the most symmetric CV curves as the indication of a good EC. Hence WO3 calcined at 400 degrees C is a potential candidate for EC material of pseudocapacitor type.