Amorphous Manganese Dioxide as a Material for an Electrochemical Pseudocapacitor

The charge storage process of amorphous hydrated manganese dioxide (MnO2) as a pseudo-capacitor involves a fast redox reaction at the electrode surface. In order to understand the charge storage mechanism of MnO2 as a pseudo-capacitor in an aqueous KCl solution, we monitored the change of the capacitance by varying the pH of the solution, the cation of the electrolyte, the concentration of the KCl electrolyte, and the solvent. The charge storage mechanism of a metal oxide electrode such as MnO2 is concluded to involve a fast redox reaction through both the potassium ion exchange, MnO2 + δK+ + δe- ⇔ MnO2-δ(OK)δ and the proton exchange, MnO2 + δH+ + δe- ⇔ MnO2-δ(OH)δ dependent upon the availability of the cations in the electrolyte.