Mechanism of zinc electrodeposition in acidic sulfate electrolytes containing Pb2+ ions

The influence of Pb2+ ions on the kinetics of zinc electrodeposition in acidic sulfate electrolyte can be interpreted in terms of a reaction model involving hydrogen adsorption and evolution, a multistep mechanism for zinc deposition and the overall reaction for zinc dissolution. From impedance data and polarization curves, it is shown that lead essentially adsorbs on the electrode and thereby strongly inhibits all the reactions taking place on the zinc electrode. In addition, the presence of Pb-ad also decreases specifically the rate constants of the reactions for zinc dissolution, hydrogen evolution, and affects the slow renewal of kink sites on the deposit surface. The slow inclusion of Pb-ad in the deposit progressively releases the sites for zinc deposition with increasing cathodic polarization.