Homogeneous versus heterogeneous electron-transfer processes in solution: a ‘fifty percent rule’ for volumes of activation

Abstract

Ac voltammetry at pressures up to 200 MPa shows that volumes of activation for heterogeneous electron transfer in three aqueous couples {[Fe(CN)₆]^3–/4–, [Co(sep)]^3+/2+ and [Co(en)₃]^3+/2+} are numerically about 50% of those for homogeneous (bimolecular) electron transfer in these same couples, with the same algebraic sign, as predicted by an extension of Marcus theory.