Application of scanning electrochemical microscopy to studies of charge propagation within polyelectrolyte coatings on electrodes

The technique of scanning electrochemical microscopy is used to examine the properties of polyelectrolyte coatings on electrodes. Coatings of protonated poly(4-vinytpyridine) exhibit time dependences of their redox conductivities with Fe(CN)_6^(3-) or IrCl_6^(2-) as counterions incorporated in the coatings. By contrast, responses obtained from coatings of Nafion show no comparable time dependence. A possible reason for the difference is suggested. Images of the two types of coatings obtained with the scanning electrochemical microscope include apparent topological features in the poly(4-vinytpyridine) coatings which are shown to arise from significant variations in redox conductivity across the surface of aged coatings rather than from true changes in the coating's dimension. In the case of Nafion coatings, only smooth surfaces are observed in scanning electrochemical microscope images whether they are recorded under conditions of positive or negative feedback. The absence of significant spatial variations in redox conductivity is believed to be responsible for the featureless images obtained with Nafion coatings