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

摘要

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 PbOn 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 PbSO4, 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 PbOn 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.