be very thin since CLF is unchanged (thickness 9 << 4)-Even if some points of the polyaniline/solution interface are still able to exchange electrons, it must be assumed that the layer is impermeable to Fe3% If not, a maximum current equal to F ADL (Co~/ 9 could be observed (DL = Fe 3 § diffusivity in the layer), the Fe 3 § being reduced at unperturbed polyaniline beneath the layer.
ConclusionImpedance methods have been applied to the study of the Fe 3+ reduction reaction on either Pt or polyaniline electrodes performed in a concentrated HC1 medium where a stable steady state may be attained. AC data analysis, according to a previously developed kinetic model (i), allows the determination of the charge transfer resistance associated to Fe 3+ reduction, in spite of the overwhelming relative weight of charging ac currents. Inspection of diffusion impedance diagrams obtained by deconvolution of CLF contribution suggested the occurrence of electron transfer at the polymer/electrolyte interface only, without Fe 3+ diffusion into the polymer layer, k ~ and bc were calculated by combining steady-state and impedance data. Polyaniline appeared to catalyze the Fe 3+ reduction, although the difference in k ~ values could be due in part to a partially inactive Pt surface.
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