Extension of the potential intervals of high redox activity and electronic conductivity of polypyrrole films on electrode surface via their electrochemical multi-cycle treatment in monomer-free solution

Abstract

Thin polypyrrole films (thickness: about 30 nm) have been deposited at electrode surface via potentiostatic oxidation of dilute (1 mM) pyrrole solution in acetonitrile (AN). It has been shown that their subsequent treatment by means of multi-cycle voltammetry within a broad potential range (up to -2.0 V vs. Ag/Ag+ in AN) leads to their "activation", i.e. to a very strong extension of their redox response region in the negative direction as well as to almost uniform distribution of the redox activity within this potential range. Region of their high conductivity under in situ conditions has also extended significantly. Spectral and electrocatalytic properties of such PPy films before and after their "activation" have been analyzed. Two parameters for characterization of the variation of film's properties in the course of its "activation" (redox efficiency of polymerization and width of electroactivity region) have been proposed. Comparison of films deposited at different potentials (from 0.6 V to 0.8 V) has revealed that the effect of their "activation" increases for lower polymerization potential. Films deposited at 0.6 V possess after their "activation" a very broad electroactivity range (almost 2.5 V) and a record high redox charge per monomer unit (its oxidation degree) inside the film in contact with AN solution, 0.45. Such unusual properties of "activated" PPy films make them prospective materials for various applications.