INFLUENCE OF PHOSPHORIC-ACID ON THE ELECTROCHEMISTRY OF LEAD ELECTRODES IN SULFURIC-ACID ELECTROLYTE CONTAINING ANTIMONY

The influence of phosphoric acid (0 to 40 g l-1) on the Pb/PbSO4 react ion and the kinetics of hydrogen evolution on pure, smooth lead and le ad alloy electrodes is studied via galvanostatic polarization in the l inear and Tafel domains with and without antimony (0 to 10 mg l-1) add ition to the H2SO4 (3 to 10 M) electrolyte. Phosphoric acid is found t o offset significantly the adverse effect of antimony. H3PO4 is also f ound to increase the hydrogen overpotential without affecting the Pb/P bSO4 reaction. This implies that the open-circuit corrosion of lead an d the consequent hydrogen evolution rate on lead are reduced in the pr esence of H3PO4. The beneficial effects of H3PO4 additive are found to be optimum at around 20 g l-1. Suppression of hydrogen evolution on t he negative electrode, a crucial criterion for sealed cell operation, can be achieved using a H3PO4 additive.