Methyl Viologen Mediated Oxygen Reduction in Ethanol Solvent: the Electrocatalytic Reactivity of the Radical Cation

The study of methyl viologen ($MV^{2+}$) mediated oxygen reduction in electrolytic ethanol media possesses potential application in the electrochemical synthesis of hydrogen peroxide mainly due to the advantages of the much increased solubility of molecular oxygen ($O_2$) and high degree of reversibility of $MV^{2+/{ullet}+}$ redox couple. The diffusion coefficients of both $MV^{2+}$ and $O_2$ were investigated via electrochemical techniques. For the first time, $MV^{2+}$ mediated $O_2$ reduction in electrolytic ethanol solution has been proved to be feasible on both boron-doped diamond and micro-carbon disc electrodes. The electrocatalytic response is demonstrated to be due to the radical cation, $MV^{{ullet}+}$. The homogeneous electron transfer step is suggested to be the rate determining step with a rate constant of $(1{pm}0.1){ imes}10^5M^{-1}s^{-1}$. With the aid of a simulation program describing the EC' mechanism, by increasing the concentration ratio of $MV^{2+}$ to $O_2$ electrochemical catalysis can be switched from a partial to a 'total catalysis' regime.