Solvent effect on electron transfer reactions: Comparison of homogeneous and heterogeneous electron exchange between V3+ and V2+ in water +t-butanol mixtures

The kinetics of homogeneous and heterogeneous electron exchange V³⁺/V²⁺ was investigated in 1 M HClO₄, water +t-butanol, mixed solvent solutions (x_t-but. varied from 0 to 0.65). Non-monotonic heterogeneous and monotonic homogeneous variations of the rate constants were observed. The solvent effect on the work of bringing the reactants from infinite separation to the reaction site was estimated with the Gouy-Chapman and Debye-Hückel approximations respectively. The homogeneous kinetics data were next used to calculate the reorganization energy in the heterogeneous reaction, λ_het. Finally the influence of the solvent composition on the rate of the electrode reaction was separated into surface and bulk effects.