Recent Development of Transition Metal Oxide Based Aqueous Supercapacitor Electrode Materials

s With the development of electric devices such as smart phones or electric vehicles, energy storage systems with high energy/power density and stable operation need to be developed together. The supercapacitors using aqueous electrolyte have great potential for electrochemical energy storage system due to their high power densities and long cyclic performances. The state-of-the-art materials for supercapacitors are carbon based porous materials having high specific surface areas and electrical conductivities. However, they have relatively low energy density that still need to enhance specific capacitance by using the nanostructure of transition metal oxide (TMO) materials. The TMOs store charge through redox reactions like battery systems and their rates are comparable to those of conventional electrochemical double-layer capacitors. In this review, we describe the fundamental principle of TMO based supercapacitors and the recent progress for realizing high performance of TMO based supercapacitors. In addition, we categorize the TMO system as single cation and mixed cations and suggest the prospects for electrochemical energy storage fields.