Proton-insertion-enhanced pseudocapacitance based on the assembly structure of tungsten oxide

The capacitances of supercapacitors with carbon and metal oxides as electrodes are usually associated with the available surface areas of the electrode materials. However, in this paper, we report that proton insertion, an unusual capacitive mechanism, may effectively enhance the capacitance of metal oxides with low surface area but specific structures. Tungsten trioxide (WO₃) as the electrode material for supercapacitors has always suffered from low capacitance. Nevertheless, enhanced by the proton insertion mechanism, we demonstrate that electrodes fabricated by an assembly structure of hexagonal-phase WO₃ (h-WO₃) nanopillars achieve a high capacitance of up to 421.8 F g^-1 under the current density of 0.5 A g^-1, which is the highest capacitance achieved with pure WO₃ as the electrodes so far, to the best of our knowledge. Detailed analyses indicate that proton insertion dominates the electrochemical behavior of h-WO₃ and plays the key role in reaching high capacitance by excluding other mechanisms. In addition, a thorough investigation on the temperature-dependent electrochemical performance reveals excellent performance stability at different temperatures. This study provides a new approach to achieving high capacitance by effective proton insertion into ordered tunnels in crystallized metal oxides, which is primarily important for the fabrication of compact high-performance energy storage devices.