Applications of Iron (Fe, Co, and Ni)‐Group Metal Compound Nanomaterials in Supercapacitors

The combined effect of accelerating global industrialization and population growth has led to a continuous rise in humanity's demand for fossil fuels. Supercapacitors (SCs), also known as electrochemical capacitors, are electrochemical energy storage devices based on charge storage at the electrode/electrolyte interface or fast reversible Faraday reactions. According to the differences in charge storage mechanisms and electrode structures, SCs are mainly divided into three categories: electric double-layer capacitors (EDLC), pseudocapacitors, and battery-type capacitors. The charge storage of EDLCs is based on the electrostatic adsorption at the electrode–electrolyte interface, which does not involve Faraday redox reactions and belongs to a physical energy storage process. The charge storage process of pseudocapacitors is different from that of EDLCs. Battery-type electrode materials undergo significant phase transitions when reacting with electrolyte ions.