Microelectrode studies of the reaction of superoxide with carbon dioxide in dimethyl sulfoxide

The reaction of superoxide with carbon dioxide is studied using voltammetry and potential step chronoamperometry at polycrystalline gold disk microelectrodes in a DMSO electrolyte. In agreement with prior work, it is found that a reaction occurs between the superoxide anion radical and carbon dioxide, effectively precluding their simultaneous detection at low levels of carbon dioxide. The reaction rate is found to be first-order with respect to both carbon dioxide and superoxide, consistent with an ECE or DISP1 type process. A rate constant is determined for this reaction based Upon two independent methods: fast scan cyclic voltammetric measurements and steady-state voltammetric signals. These methods yield a consistent rate constant of 3.7 +/- 1.6 x 10(5) M-1 s(-1). Potential step chronoamperometric measurements reveal that oxygen adsorbs onto a gold electrode surface, to form a monolayer both in the presence and absence of carbon dioxide. A rate constant for the reduction of surface-bound oxygen to superoxide is reported.