Use of Normal Pulse Voltammetry in Diagnosing Electrode Kinetics of Octacyanomolybdate(IV/V) Complexes Bound Electrostatically to Graphite Electrodes Coated with Polyelectrolytes

Abstract

Abstract An electron transfer process of [Mo(CN)8]4−⁄3− redox couple at the graphite electrode/protonated poly(4-vinylpyridine) (PVP) interfaces was examined by the normal pulse voltammetry. It became apparent that electrode reaction of the electroactive species confined in the polymer film on electrode surface obeys the conventional Butler-Volmer equation which characterizes the ordinary electrode reaction at electrode/solution interface. From the analysis of the dependences of the current-potential curves upon the sampling time the relevant kinetic parameters (i.e., the standard rate constant, k° and the transfer coefficient, α) of the electrode reaction were evaluated. The value of k° decreased from 9.7×10−4 to 1.7×10−4 cm s−1 and the value of α was almost constant (0.50), when the molar ratio of the incorporated [Mo(CN)8]4− to pyridine group of the PVP film, ΓM⁄ΓPVP, was increased from 0.0025 to 0.22. The apparent diffusion coefficient, Dapp, for the process of charge transport within the film was also determined from the dependence of the limiting current upon the sampling time. The value of Dapp decreased from 4.4×10−8 to 2.5×10−9 cm2 s−1, when the ratio ΓM/ΓPVP was increased from 0.0025 to 0.22.