Metal Oxides for Supercapacitors

Presently, the progression of electrical devices and consumer electronics is hindered by the energy storage devices. Supercapacitors (SCs) have been widely used as one of the most promising energy storage devices because of their high energy and power density, long cycle life, and good safety in wide redox potential. Improving and enlarging the utilization range of SCs is in urgent need of the research for the next-generation energy storage devices.

Most of the research and development on SCs focus on electrode materials. Some attempts have been directed toward increasing the energy density by employing electroactive materials, such as metal oxides. Complex metal oxides, especially in the form of nanostructures, have attracted increasing attention as promising electrode materials for SCs owing to their superior structure features compared to the simple binary metal oxides. Furthermore, the utilization of nanocomplex metal oxides has led to an improvement of specific capacitance, charge–discharge (CD) rate, power and energy density, and stability of SCs as a result of their enlarged specific surface area, which allows fast electrolyte-ion diffusion. Investigation of the effective features of the electrode material such as particle, crystallite size, surface area, pore size, and phase composition is applicable by characterization routes. Moreover, investigation of specific capacitance, cycle stability, Coulombic efficiency, faradic resistance, and double-layer capacitance can be carried out using electrochemical measurements such as cyclic voltammetry (CV), CD, and electrochemical impedance spectroscopy (EIS).