The performance of Pb-MnO₂ and Pb-Ag anodes in 2 Mn(II)-containing sulphuric acid electrolyte solutions

In this study, electrochemical performances of the Pb-MnO₂ composite anodes in sulphuric acid electrolyte containing different manganese concentrations were investigated. The anodic electrodeposited MnO₂ layers on the composite anodes were studied and their properties were compared with those of an industrial Pb-Ag anode. The electrochemical impedance spectroscopy (EIS) and potentiostatic polarizations were accompanied by chemical analysis of the electrolyte to investigate the Mn(II) oxidation and oxygen evolution rates on the fresh anodes. The long term effect of the deposited MnO₂ on the electrocatalytic properties of the anodes was studied by galvanostatic polarizations. The results revealed that the Pb-MnO₂ anodes operate at lower potentials than the Pb-Ag anodes in a Mn-free electrolyte, indicating higher electrocatalytic activity of the composite anode. The Mn(II) oxidation proceeded at different rates on the Pb-Ag and Pb-MnO₂ anodes. The oxygen evolution reaction was depolarized in the presence of Mn(II) ions. However, formation of the MnO₂ layers might lead to higher anodic potentials. Scanning electron microscopy (SEM), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) were utilized to characterize the deposited MnO₂ layers and also the corrosion product layers on the anodes. The MnO₂ layers on the anodes were found to have different properties. While MnO₂ layers on the composite anodes were uniform, compact and adhesive, the deposited layers on the Pb-Ag anodes were flaky, porous, and loosely adhered. These layers provided the anodes with different degree of protection against electrochemical oxidation.