Electrocatalysis of Anodic Oxygen‐Transfer Reactions: Activation of Electrodes in 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 electrodes in . DMSO was virtually unreactive at pure electrodes electrodeposited from acidic media. However, well‐defined anodic waves with transport‐limited current plateaus were obtained for up to 100 mMDMSO by addition of as little as 10 μM Bi³⁺. The product of DMSO oxidation was determined to be dimethyl sulfone. 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 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 values for the respective half reactions. This is explained as the consequence of a common rate‐controlling step which is the discharge of at the Bi sites to produce adsorbed hydroxyl radicals (^.OH_ads) 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⁺.