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°C, 400°C, 500°C and 600°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°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°C is a potential candidate for EC material of pseudocapacitor type.