engleski

Impedance Study of the PbO/PbO_n/PbO_2 Transformations in the Anodic Layer Formed on Pb and Pb-Sb Electrodes

It has been established that antimony, widely used as an alloying additive in lead alloys for casting lead-acid battery grids, not only significantly affects the casting and mechanical properties of the alloys, but also has a strong impact on the electrochemical processes at the positive plate of the battery. The PbO/PbO_n/PbO_2 transformations in the anodic layer formed on Pb and Pb-Sb electrodes were investigated in situ using the cyclic voltammetry and impedance spectroscopy techniques. The investigations were performed on pure Pb(99.998 wt%) and Pb-Sb alloys with Sb content of 1.3, 2.7 and 3.5 wt% in 0.5 M H_2SO_4 solution. Antimony oxidation in Pb-Sb alloys begins at potential values at which PbO formation takes place under the PbSO_4 per-selective membrane. It was found that antimony oxidation in alloy changes the composition of the anodic layer and simultaneously to the formation of lead-oxide compounds, substituted Pb-Sb non-stoichiometric oxides are formed. Formation of the relatively conductive non-stoichiometric oxides and their stability at potentials more negative than the equilibrium one for PbO_2/PbSO_4 electrode may influence the capacity of the positive lead-acid battery plate. During discharge, the Pb_(1-x)Sb_xO_n oxide preserves the electronic contact between the grid and positive active material of the plate down to more negative potentials before the high ohmic PbO layer is formed and the plate is strongly polarized. Impedance measurements confirm also cyclic voltammetry findings that antimony retards anodic oxidation of PbSO_4 into PbO_2.

lead; lead-antimony alloys; anodic oxide films; lead/acid batteries; EIS

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