APPLICATION OF AN ELECTROCHEMICAL QUARTZ-CRYSTAL MICROBALANCE TO A STUDY OF THE ANODIC DEPOSITION OF PBO2 AND BI-PBO2 FILMS ON GOLD ELECTRODES

The net rate of change in surface mass measured with respect to faradaic charge (DELTAm/DELTAq) is calculated for electrodeposited films from the slopes of plots of frequency vs. charge (df/dq). Abrupt changes in df/dq observed early in the deposition of PbO2 and some Bi-PbO2 films correspond to the transition form two-dimensional island growth to one-dimensional growth of the continuous films. Further, these changes in df/dq are a consequence of differences in the surface hydration of the deposited films in comparison with the AuO substrate. XPS data indicate that Bi/Pb ratios in Bi-PbO2 films correspond approximately to the [Bi3+]/[Pb2+] ratios in the deposition solutions. Further, voltammetric data for oxidation of dimethylsulfoxide indicate the catalytic activity of the Bi-PbO2 films increases with the increased Bi/Pb ratios in these films. Nevertheless, limiting values of DELTAm/DELTAq are virtually identical for the deposition of the Bi-PbO2 films containing variable Bi/Pb ratios. The precision of the EQCM data does not allow designation of exact compositions of these various Bi-PbO2 films. Nevertheless, we speculate that the EQCM data indicate the deposition of Bi3+ as Bi(V) with some Bi(IV), and the incorporation of H2O in the Bi-PbO2 films. Limiting values of DELTAm/DELTAq = ca. 1.22 mg C-1 for thick lead oxide films deposited in the absence of Bi3+ are within experimental error of the theoretical value of 1.24 mg C-1 for pure PbO2, and we conclude there is no evidence from the EQCM data for incorporation of H2O and/or supporting electrolyte into these films.