Investigation of Pseudocapacitive Charge-Storage Behavior in Highly Conductive Ordered Mesoporous Tungsten Oxide Electrodes

Herein, a pseudocapacitive charging behavior of highly conductive ordered mesoporous tungsten oxide (m-WO 3-X ) is investigated. For this purpose, various electrochemical analysis methods such as cyclic voltammetry (CV), galvanostatic charge–discharge experiment and electrochemical impedance spectroscopy (EIS) were employed. From CV experiment, a relationship analysis between voltammetric charge and scan rate resulted in total (67 C g –1 ), outer (61 C g –1 ) and inner charge (6 C g –1 ), which was related with the well-developed crystalline structure of m-WO 3-X . In galvanostatic charge–discharge profiles with change of applied current, a more severe decrease of cathodic capacity than the anodic one was observed, which was attributed to larger cathodic resistance. This resistance dependency on potential was clarified with EIS fitting analysis. Here, the charge transfer resistance and Warburg diffusion resistance became larger with increasing potential, which was relevant to the change of oxidation state during redox reaction. Using these electrochemical analysis results, a schematic illustration of the pseudocapacitive charging mechanism was proposed.