CHARACTERIZING THE EARLY STAGES OF ELECTROCHEMICAL PHASE-FORMATION OFLEAD SULFATE FILMS

A semiquantitative evaluation of lead sulfate film formation on lead i n sulfuric acid solution was done by current-time transient studies. T he 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 w ell as screening of expanders and their concentration for lead-acid ba ttery negative plate operation. The mechanism of formation of Pb2+ (Pb SO4) 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 dissolutio n-precipitation mode. The kinetics of lead sulfate formation do not fo llow any of the reported/known models. The dissolution-precipitation m odel coupled with nucleation and a growth model/theory is indicated.