ELECTROCATALYSIS OF ANODIC OXYGEN-TRANSFER REACTIONS - APPLICATION OF AN ELECTROCHEMICAL QUARTZ CRYSTAL MICROBALANCE TO A STUDY OF PURE AND BISMUTH-DOPED BETA-LEAD DIOXIDE FILM ELECTRODES

Ratios of the change in surface mass corresponding to a change in charge (Δm/Δq) were determined for the electrodeposition of thin films of pure PbO2 and Bi-doped PbO2 at Au-film electrodes in 0.1M HClO4, using an electrochemical quartz microbalance. The value Δm/Δq = 1.26 ± 0.04 mg C−1 obtained for pure PbO2 films is in good agreement with the theoretical value of 1.24 mg C−1. A larger value, Δm/Δq = 1.32 ± 0.03 mg C−1, obtained for the Bi-doped PbO2 films, is concluded to result from the co-deposition of some ClO4 − with Bi(V) in the mixed-oxide film. Bismuth(III) was determined to be anodically adsorbed as Bi(V) at pure PbO2 surfaces for E > 1.45V vs. Ag/AgCl with Δm/Δq = 1.72 ± 0.02 mg C−1 in 0.1M HClO4 and 1.30 ± 0.03 mg C−1 in 1M HNO3. The PbO2-film electrodes with adsorbed Bi(V) are active for various anodic oxygen-transfer reactions, including the oxidations of Mn(II) to MnO4 − and DMSO to DMSO2. Experimental results are interpreted to be consistent with a mechanism proposed previously, in which the Bi(V) sites have a lower overpotential for anodic discharge of H2O to produce O2. It has been proposed that adsorbed hydroxyl radicals (·OHads) generated in the O2 evolution mechanism are consumed by oxygen-transfer steps, required in many oxidation processes. © 1990, The Electrochemical Society, Inc. All rights reserved.