CoCl₂ Designed as Excellent Pseudocapacitor Electrode Materials

The major limitation of supercapacitors is their low energy densities compared with battery systems. However, there has not been an advanced charge storage mechanism for increasing the electrochemical performance of pseudocapacitors. For the first time, we reported that water-soluble CoCl2 electrodes can show a reversible redox reaction of Co2+ ↔ Co3+ ↔ Co4+ on the electrode and deliver very high specific pseudocapacitance of ∼1962 F/g. Commercial CoCl2 salt was used directly as pseudocapacitor electrodes in an aqueous electrolyte neglecting the complex synthesis procedures. We further provided electronegativity as a theoretical guideline to identify the promising active metal cations in our pseudocapacitor system. The new charge storage mechanism based on active cations offers critical insights to the rational design of a new generation of energy storage devices.