Electrodeposition of Co-doped lead dioxide and its physicochemical properties

An investigation on the electrodeposition of cobalt-doped lead dioxide has been carried out, as part of a study ultimately aimed at producing anodes with improved electrocatalytic activity and stability. An assessment of the influence of different experimental parameters on the amount of incorporated Co was made for PbO2 films grown either at constant current or constant potential. The Co content in PbO2 decreases with increasing temperature and pH of the deposition solution, probably due to the fact that increasing the growth electrolyte temperature from 25 to 65 degreesC causes a decrease of the deposition potential from 1.5 to 1.4 V. Similarly, a rise of the electrolyte pH brings about a decrease of the electrodeposition potential. The same electrodeposition kinetics are obeyed in the absence and in the presence of Co2+ in solution. In the potential region where the Pb(II) oxidation becomes diffusion controlled, the corresponding limiting current decreases when Co2+ is present. This is due to an enhancement of the parallel O-2 evolution process. Experiments showed that Co2+ is weakly adsorbed on PbO2, and that the adsorption follows Langmuir conditions. Surface analysis by XRD and XPS of the Co-doped PbO2 films does not reveal major changes compared to undoped samples. Tritium radiotracer experiments show that the effect of Co-doping on incorporation of protons is appreciable in films deposited at relatively high temperature (65 degreesC). In this case, as a function of electrodeposition time, the amount of incorporated tritium first increases then decreases to the same value measured for undoped PbO2. This behaviour is likely to be due to substitution of Pb(IV) with Co(II) followed by oxidation of the incorporated Co(II) to Co(III) as electrodeposition proceeds. (C) 2002 Published by Elsevier Science B.V.