Electrochemical Synthesis of Beta- and Gamma-Manganese Dioxides under Hydrothermal Conditions

The hydrothermal-electrochemical method has been used for the synthesis of manganese dioxides from acidic solutions. This method produced manganese dioxides of either the β- or γ-structure type. At pH 1 and 130°C, pure was formed; this was the first time that this structure has been obtained electrochemically. At 113 or 92°C, mixtures of β- and were obtained, and the content decreased with temperature. Increasing the acidity at 92°C led to the formation of pure with lower levels of pyrolusite intergrowth and microtwinning defects compared to prepared by traditional electrochemical syntheses.