Manganese dioxide electrode shows reversible charge storage capacity, if the charge-discharge process is limited to 0.3e − exchange. Addition of small amount of Bi 2 O 3 to manganese dioxide induces reversibility with an exchange of 2e − /Mn. Nickel hydroxide is known to reversibly exchange 1e− . In spite of isostructural relationship between the cobalt hydroxide, nickel hydroxide and manganese dioxide, cobalt hydroxide does not show any electrochemical activity. Bi 2 O 3 modified cobalt hydroxide electrodes exchanges 0.3-0.5e − /Co during the charge discharge process. The oxidation-reduction process in cobalt hydroxide and Bi 2 O 3 modified cobalt hydroxide electrodes were monitored using the PXRD patterns.