Preparation and properties of some chemical and electrochemical gamma-MnO2

Chemically prepared electrolytic gamma -MnO2 and an electrodeposited MnO2 doped with Ce(III) were subjected to physicochemical studies. X-ray diffractometry, density measurements, chemical analysis and thermal analysis were used to determine the structure and chemical disorder present. The samples prepared chemically (CMD) or electrochemically (EMD) showed a variable amount of de Wolff disorder (P-r) and microtwinning (T-w). Manganese dioxide prepared in the presence of Ce(III) showed appreciable decrease in de Wolff defect and a large amount of microtwinning. Thermal analysis showed a loss of weight due to the physically adsorbed and the structural (OH) water, from which the activation energy was calculated. Chemical composition and formulae calculated on the bases of cation vacancy model, cleared that Ce(III)-doped sample has a remarkable increase in the vacancies population associated with higher structural water content. This leads to lower activation energy of water release, and consequently it is supposed to acquire higher electrochemical activity.