Use of Alternating Current Impedance Method in Diagnosing Electrode Kinetics of [Fe(CN)6]4−⁄3− Complex Confined to Protonated Poly(4-vinylpyridine) Film on Graphite Surfaces

A “heterogeneous” electron-transfer process of [Fe(CN)6]4−⁄3− redox couple, which was confined electrostatically to the protonated poly(4-vinylpyridine) (PVP) film, at basal-plane pyrolytic graphite (BPG) electrode/ PVP film interfaces and a “homogeneous” charge-transport process within the PVP film were examined by alternating current (ac) impedance method. The obtained impedance loci were found to correspond to those expected for the electrochemical impedance expressed by “Randles’s equivalent circuit.” The relevant kinetic parameters (i.e., the standard rate constant, k° and the cathodic transfer coefficient, α) of the electrode reaction, the apparent diffusion coefficients, Dapp, for the “homogeneous” charge-transport within the film, the double-layer capacity, Cd1 and the solution resistance, Rsoln were determined at various concentrations of [Fe(CN)6]3− in PVP coatings. The obtained Dapp, k°, and α values were compared with those recently obtained by normal pulse voltammetry. In addition, an equivalent circuit model is given for the impedance obtained for the redox reaction on a BPG electrode coated with a protonated PVP confining [Fe(CN)6]4−⁄3− couple.