Temperature effects in the electrochemical behaviour of cycled lead electrodes in HCl solutions

Abstract

The electrochemical behaviour of cycled lead electrodes has been investigated in HCl solutions in the temperature range −6° to 30°C. Because of the low ionic strength of solution below ~0.8 M, and the associated ir drop problem, solutions stronger than 1.0 M were principally considered. In weaker solution (0.1–0.8 M) only derived current functions were analysed, whilst all potential-dependent parameters were rejected. Results are reported for both stationary and rotatiang disc electrodes. Because of the chemical dissolution of the surface layer of PbCl 2 formed on anodic scan, measurements were confined to time-scales of < 1 s. By applying these strict criteria, the overall reaction scheme was deduced. In particular, the kinetics of passivation were found to involve the three-dimensional growth of isolated PbCl 2 nuclei, which slowly dissolve into solution. At extreme anodic potentials, or at low temperature, passivation occurs by progressive, two-dimensional growth under diffusion control. A simultaneous electrochemical dissolution of Pb 2+ at somewhat more negative potentials is noted, for which the rate-determining step is the diffusion of lead ion complexes away from the electrode surface. The nature of the reactivation of the electrode at extreme anodic potentials is also discussed.