Electrochemical behaviors of co-deposited Pb/Pb–MnO2 composite anode in sulfuric acid solution – Tafel and EIS investigations

Abstract

The oxygen evolution kinetics and anodic layer properties of Pb/Pb–MnO2 composite anode during the 72h galvanostatic electrolysis in H2SO4 solution were investigated with Quasi-stationary polarization (Tafel) and Electrochemical Impedance Spectroscopy (EIS) techniques. The results revealed that the anodic activity and reaction kinetics varied a lot during the electrolysis for it is a process indicating the formation and stabilization of anodic layer. At the very beginning of electrolysis, the composite anode exhibited very high oxygen evolution activity since the reaction was controlled by the transformation step of intermediates. Then, its oxygen evolution activity was largely diminished and the rate determination step (rds) became the formation and adsorption of first intermediate, S–OHads. In the prolonged electrolysis, the anodic potential gradually decreased and the final stable value was comparable to industrial Pb–Ag (1.0%) anode. On the stable anodic layer after 72h, the oxygen evolution reaction (OER) was still controlled by the formation and adsorption of intermediate, and the adsorption resistance took a dominant part in the whole impedance. Besides, compared with Pb–Ag and Pb anode, although OER at the stable state were all controlled by the intermediate adsorption process, the adsorption resistance of Pb/Pb–MnO2 anode was much smaller than the other two due to the existence of MnO2 particles and large amount of β-PbO2 in the stable anodic layer.