Preparation and properties of some chemical and electrochemical gamma-MnO2

Chemically prepared electrolytic gamma -MnO2 and an electrodeposited MnO2 d oped with Ce(III) were subjected to physicochemical studies. X-ray diffract ometry, density measurements, chemical analysis and thermal analysis were u sed to determine the structure and chemical disorder present. The samples p repared chemically (CMD) or electrochemically (EMD) showed a variable amoun t of de Wolff disorder (P-r) and microtwinning (T-w). Manganese dioxide pre pared in the presence of Ce(III) showed appreciable decrease in de Wolff de fect 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 formul ae calculated on the bases of cation vacancy model, cleared that Ce(III)-do ped sample has a remarkable increase in the vacancies population associated with higher structural water content. This leads to lower activation energ y of water release, and consequently it is supposed to acquire higher elect rochemical activity.