The solvent friction mechanism for outer-sphere electron exchange at bare metal electrodes. The case of Au/Ru(NH3)(6)(3+)/(2+) redox system

The heterogeneous rate constant for the Ru(NH3)63+/2+ electron exchange at the bare gold electrode displays a power-law dependence on the solution viscosity (varied by addition of glucose, 0–600 g/l) with a negative power index of d delta=1, indicative of the ‘‘full’’ solvent friction (adiabatic) mechanism for the intrinsic charge-transfer step. Comparison with related processes suggests that this mechanism mainly occurs at bare metal electrodes irrespective of the reactants' charged state and the method of viscosity variation. The adiabatic regime operates notwithstanding the presence of at least one layer of solvating water, and/or specifically adsorbed ions, contributing to the charge-transfer distance.