The electroreduction of oxygen in aprotic solvents

The electrochemical reduction of oxygen in a range of six polar aprotic solvents is investigated via linear sweep voltammetry at platinum, gold, and carbon fibre microelectrodes. Values for the standard heterogeneous electron transfer rate constant (k0) are reported, and in all cases follow the trend with electrode material of k0(C) > k0(Pt) ~ k0(Au). The variation in k0 with solvent is discussed in terms of the Debye model and a dependence on the longitudinal dielectric relaxation constant (τL) is found of the form k0 ∝ τL−θ. Static solvent effects are accounted for via consideration of both spherical and connected-spheres models of solvation, and it is found that θ ≈ 0.65 indicating that the reduction of dioxygen in these solvents is a non-adiabatic outer-sphere electron transfer.