Influence of polarisation time and Mn²⁺ on the electrochemical behaviour of different lead silver anodes

The influence of polarisation time and Mn content on the electrochemical behaviour of different lead silver anodes in sulphuric acid electrolyte during decay periods has been studied. After 1, 5 and 10 h polarisation followed by one hour decay in zinc electrolyte in the presence of Mn2+, the corrosion current density of Pb-0.5% Ag was higher than that of Pb-0.6% Ag anode and even higher than that of Pb-0.7% Ag anode. It was also found that during 1 h of decay after 5 h polarisation study in the presence and the absence of Mn2+, the Pb-Ag anodes containing different silver contents have better oxide film and less corrosion current density than that of 1 and 10 h of polarisation. Electrochemical impedance results confirmed the mentioned tendency with and without Mn2+ additions. Scanning electron microscope (SEM) analysis shows that the presence of MnO2 on the anode surface provides a protective barrier against leakage of Pb2+ ions into the solution.