Mechanism of formation of anodic excursion peaks on lead electrode in sulfuric acid

Abstract

Potential step and linear sweep voltammetry are proposed in combination for the anodic excursion peaks (AEPs) measurement of lead in sulfuric acid during cathodic scanning in the positive potential range. The overall procedure of measurement is composed of three steps. The first one is to polarize the lead electrode with negative potential, which is necessary for passivated PbSO 4(O) formation. Then, the polarization potential is stepped to positive to make sure that pure Pb could be oxidized to produce PbO n intermediate. Finally, a low-rate cathodic linear sweep voltammetry measurement is conducted in a small potential range. Four AEPs have been observed without reduction of PbO 2 to PbSO 4, which is in confliction with the conventional understanding that AEPs would appear accompanying with a large reduction peak for PbO 2 discharge. A new mechanism is therefore proposed that AEPs corresponds to the oxidation of PbO n intermediate in the cathodic scanning, so AEPs can be used to indicate the difficulty for the oxidation of Pb to PbO 2, and could be applied to characterize the corrosion resistance of lead alloy grid in the positive plate of a lead-acid battery.