The apparent standard rate constant, k(0), for a Pt/hexacyanoferrate(II/III) electrode process, known to be strongly dependent on the nature and the concentration of supporting electrolyte (viz., of its cationic component), is proven to also display a lateral dependence on the solution viscosity (water/glucose mixtures, 0.24-2.0 M in KCl and LiCl). The viscosity performance is complementary to the catalytic effect of cations and seems to operate independently. The catalytic role of cations is discussed in terms of the preequilibrium concept, considering the influence of a double-layer potential on the effective concentration of reactant ions at the active site near the electrode, k(0) is inversely proportional to the solution viscosity, indicative of strong solute/solvent and intersite electronic coupling, provided that the observed relationship is a manifestation of the solvent friction ("overdamped") mechanism for an elementary electron-transfer step.