Influence of H3PO4 on the electrochemical behaviour of the PbO2 electrode

Abstract Passivation caused by sulfate formation within corrosion layers during cyclic deep discharge of PbO 2 electrodes with grids free of antimony can be diminished by addition of phosphoric acid to the electrolyte. The mechanism was studied by means of cyclovoltammetric and potential-step measurements, X-ray diffraction and scanner electron microscopy (SEM). It was observed that phosphate ions adsorbed specifically on lead dioxide influence nucleation and nuclei growth of PbO 2 . During discharge of PbO 2 formed in this manner a PbSO 4 of extremely fine grain and dense structure was found, which protects PbO 2 against further discharge and thus prevents an irreversible sulfation of the corrosion layer.