ELECTROCATALYSIS OF ANODIC OXYGEN-TRANSFER REACTIONS - ACTIVATION OF PBO2-FILM ELECTRODES IN 1.0M HCIO4 BY ADDITION OF BISMUTH(III) AND ARSENIC(III,V)

The electrocatalytic effect of added Bi3+ was studied for the anodic response of dimethyl sulfoxide (DMSO) at PbO2-film electrodes in 1.0M HClO4. DMSO was virtually unreactive at pure PbO2-film electrodes electrodeposited from acidic media. However, well-defined anodic waves with transport-limited current plateaus were obtained for up to 100 mM DMSO by addition of as little as 10 µM Bi3+. The product of DMSO oxidation was determined to be dimethyl sulfone (DMSO2). The electrode activity is concluded to be the result of adsorbed Bi3+ and/or Bi5+ which function to mediate the oxygen-transfer step in the anodic reaction mechanism. The E1/2 values for DMSO and several additional compounds were determined to be virtually equivalent (1.65–1.71V vs. SCE) in spite of large differences in the E° values for the respective half reactions. This is explained as the consequence of a common rate-controlling step which is the discharge of H2O at the Bi sites to produce adsorbed hydroxyl radicals (-OHads) which are subsequently consumed in the oxidation process. Large concentrations of Bi3+ (>>10 µM) severely inhibited the electrocatalytic reaction. The addition of As3+ and As5+ also resulted in the electrocatalytic oxidation of DMSO; however, the concentrations required to produce transport-limited signals were much larger than needed for Bi3+. © 1990, The Electrochemical Society, Inc. All rights reserved.