| Abstract: | Electron transfer processes for selected redox systems (ferrocene0/+, decamethylferrocene0/+, N,N,N′,N′‐tetramethyl‐1,4‐phenylenediamine0/+, 7,7,8,8‐tetracyano‐quinonedimethane0/?/2?, cobaltocene0/+, C600/?, and benzoquinone0/?) at electrodes modified by precipitation of electrochemically inactive [MIII(bpy)3](ClO4)3 (M=Co and Fe, bpy=2,2′‐bipyridine) layers have been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance studies. The mediation of heterogeneous electron transfer is observed for these systems. For an electrode modified with [MIII(bpy)3](ClO4)3, the rate of the electrocatalytic mediation process depends on the formal potential of the redox system. If the formal potential of the redox system is close to the potential of [CoII(bpy)3]2+ oxidation (as is the case with the decamethylferrocene0/+, N,N,N′,N′‐tetramethyl‐1,4‐phenylenediamine0/+ and 7,7,8,8‐tetracyanoquinonedimethane0/? systems), the rate of the electrode reaction is limited by the rate of the chemical reduction of the [CoIII(bpy)3](ClO4)3 solid phase by the reduced form of redox couple. For C60 and benzoquinone, which have more negative formal potentials for reduction, the rate of diffusion of the electroactive reactant to the electrode surface limits the rate of electrode process. The kinetics of mediated electrocatalysis are also affected by the solvent. In the case of the Fe(III)‐based layer, the diffusion of the electroactive reactant in the solution is the rate determining step for the catalytic process at the modified electrode for all studied systems. Electrodes modified with [FeIII(bpy)3](ClO4)3 have been used for the quantitative determination of electroactive compounds. For ferrocene and decamethylferrocene, a linear relationship between the catalytic reduction current and the concentration of reactant in the solution has been observed over the concentration range from 1 to 50 mM. |
