Electrochemistry of oxygen and superoxide ion in dimethylsulfoxide at platinum, gold and mercury electrodes

Abstract

The electrochemistry of dissolved oxygen and of superoxide ion in dimethyl-sulfoxide solutions has been studied at platinum, gold and mercury electrodes using voltammetric and chronopotentiometric techniques as -well as controlled-potential coulonietry. In the absence of protic electrolytes and solvents, oxygen is reduced in two one-electron steps, first to superoxide ion at a potential of −0.75 V vs. S.C.E. and then to peroxide ion at a potential of −2.02 V vs. S.C.E. The second step is not observed with a platinum electrode. Superoxide ion is oxidized to oxygen at −0.73 V and is reduced to peroxide ion at −2.02 V. Peroxide ion is oxidized directly to oxygen at +0.75 V by a two-electron process. In the presence of a protic electrolyte (0.1 F NH 4ClO 4) oxygen is reduced in one step to hydrogen peroxide at −0.28 V. The kinetic parameters for the oxygen-superoxide ion electrode reaction are essentially the same for all three electrodes; the average for all determinations is: α n a = 0.55; k s,h 0 = 10 −3. The diffusion coefficients for oxygen and superoxide ion in 0.1 F (Et 4)NClO 4-DMSO solutions have been evaluated; D o 2 = 3.23·10 −5 cm 2 sec and D o 2 = 1.08·10 −5 cm 2 sec. Mechanisms are proposed for the electrode reactions and for disproportionation reactions that are consistent with the observed experimental data.