Recent development of metal hydroxides as electrode material of electrochemical capacitors

Electrochemical capacitors, also known as supercapacitors, are energy storage devices, characterized by rapid rates of charging and discharging and high power density. In recent years, electrochemical capacitors have attracted significant attention as 'bridges' for the power/energy gap between traditional capacitors and batteries/fuel cells. The integrated performance of an electrochemical capacitor is essentially determined by its electrode materials. This is a review of electrode materials for electrochemical capacitors, chiefly concerning transition metal hydroxides. In this work, we focused particularly on recently published reports using cheap metal hydroxides as electrode materials for electrochemical capacitors, based on classification of metal hydroxide by composition and microstructure. Some important experimental data on this issue are indicated and summarized. Furthermore, a brief discussion of future development, challenges, and opportunities in this area is also provided.