Hydrated layered manganese dioxide Part II.: Electrochemical behaviour of some hydrated layered manganese dioxides in alkaline electrolytes

The electrochemical behaviour of some hydrated layered manganese dioxides previously prepared and characterised was investigated by galvanostatic and potentiostatic studies at different conditions of temperature, type of electrolyte and counter electrode, number of cycles and depth of reduction. Reversible range was found to be a homogeneous reaction, which is limited up to 0.23 e(-)/f.u., whereas the major theoretical capacity is consumed in two heterogeneous reduction reactions yielding Mn(OH)(2) at the end. Spinel-like phases such as hausmannite and hetacrolite are formed during the heterogeneous stage. The formation of the spinel-like phases was found to decrease at low temperature in the absence of aggressive ions such as Zn2+ and at shallow depth of reduction. The mechanism of the electrochemical reduction of the heterogeneous stage is suggested to proceed via an intermediate with the hydrotalcite structure, which undergoes conversion to Mn3O4. The chemical reduction of manganese dioxides was also investigated and was found to support this suggestion. (C) 2002 Elsevier Science B.V. All rights reserved.