VOLTAMMETRIC RESPONSE OF DIMETHYL-SULFOXIDE AT GOLD ELECTRODES MODIFIED BY THIN-FILMS OF BISMUTH-DOPED LEAD DIOXIDE

The anodic oxidation of dimethyl sulphoxide (DMSO) to DMSO2 is representative of numerous anodic oxygen-transfer reactions that do not occur at appreciable rates at conventional anodes, e.g., noble metals and carbon. However, useful voltammetric waves can be obtained at noble metal electrodes modified by thin films of electrodeposited, bismuth(V)-doped lead dioxide (Bi-PbO2). Voltammetric data for anodic deposition with cathodic stripping of Bi-PbO2 films are examined for gold rotated disk electrodes in 1.0 M HClO4 containing Pb2+ with Bi3+. Evidence is shown that ultra-thin films (< ca. 1-mu-m) of a reduced oxide, designated "Bi-PbO", remain on the Au substrate when thick Bi-PbO2 films (> ca. 10-mu-m) are voltammetrically stripped under rapid potential scan. The ultra-thin films possess a larger atomic ratio of Bi/Pb than the original thicker films and, following reoxidation to Bi-PbO2, they display greater catalytic activity. The effect is interpreted on the basis of mediation of the oxygen-transfer step.