Role of hydration water in the reduction process of PbO2 in lead/acid cells

The influence of 'hydrogen loss' on the electrochemical properties of both alpha-PbO2 and beta-PbO2 was studied using galvanostatic discharge and cyclic voltammetry. The thermal decomposition of electroformed PbO2 shows two types of hydration water: the first type, which disappears at low temperature, is adsorbed on the surfaces of the PbO2 particles, and the second one is localized within the PbO2 crystal structure. The reduction process of PbO2 in lead/acid cells is mainly determined by diffusion processes within the oxide. The hydrogen diffusion coefficient (D) over tilde(H) in lead dioxide has been determined at 25 degrees C; the values obtained are between 0.42 and 1.67 X 10(-7) cm(2) s(-1). The removing of structurally bonded' water, by heating the samples at 230 degrees C, affects considerably the electrochemical properties of PbO2 and leads to a decrease in (D) over tilde(H).