Role of Phosphoric Acid on the Corrosion Performance of Pb-1.7%Sb Grid of Lead-Acid Batteries

The corrosion behavior of a commercial Pb-1.7%Sb grid of lead-acid batteries under open circuit conditions in 5 M H2SO4 in the presence of phosphoric acid is studied by electrochemical impedance spectroscopy and cyclic voltammetry. Dependence of corrodibility of the alloy on H3PO4 concentration is weak up to 0.7M. After days of corrosion, the corrosion rate in the presence of H3PO4 is slightly higher than in its absence, due to retardation of the growth of an insulating PbSO4 layer that acts as an effective diffusion barrier of the corrosive species. The electronic and diffusion properties of the passive layer formed in the presence of H3PO4 are substantially inferior. Cyclic voltammetry indicates a decrease in amounts of PbSO4 and Sb2O3 formed in the presence of H3PO4 and with increasing its concentration. Also, the amount of PbO formed beneath the PbSO4 layer increases with increasing H3PO4 concentration on the expense of the amount of PbSO4.