Characterizing the Early Stages of Electrochemical Phase Formation of Lead Sulfate Films

A semiquantitative evaluation of lead sulfate film formation on lead in sulfuric acid solution was done by current-time transient studies. The effects of acid concentration, potential, and expander are explored. Crucial parameters of film formation and passivation are identified which could be used for selection of an electrolyte concentration as well as screening of expanders and their concentration for lead-acid battery negative plate operation. The mechanism of formation of Pb 2+ (PbSO 4 ) from lead was confirmed to involve two, one-electron, steps ; the second electron transfer being the rate-determining step. Expanders do not affect the Tafel slope but favor the mechanism through dissolution-precipitation mode. The kinetics of lead sulfate formation do not follow any of the reported/known models. The dissolution-precipitation model coupled with nucleation and a growth model/theory is indicated.