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Structural Electrochemistry: Conductivities and Ionic Content from Rising Reduced Polypyrrole Films

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Abstract

Free-standing polypyrrole films are submitted in NaCl aqueous solutions with different potentials corresponding to the swollen, closed, or reduced and rising conformational packed states, defined from the closed coulovoltammetric responses in the potential range between –1.5 and 0.65 V versus Ag/AgCl. Decreasing anion content from rising reduced and conformational packed films is detected by energy-dispersive X-ray spectroscopy (EDX) analysis. The cation, Na+, is not present in the studied samples. At the closing potential, the film keeps over 30% of the counterions present in a fully oxidized film. The film reduction-compaction process at high cathodic potentials consumes over 15% of the full redox charge, expelling a similar percentage of counterions. By using free-standing PPy-DBS films, the Na+ content increases for rising reduced states, but some increase of the chloride content is attained for deep oxidized and packed states. This polypyrrole blend experiences a major exchange of cations for charge balance. Some polypyrrole chains not balanced by DBS require perchlorate exchange at high anodic potentials. The continuous decrease of anion content promotes in polypyrrole films a parallel decrease of the electronic conductivities obtained in nitrogen atmosphere. Ionic content and conductivities in polypyrrole films support that the two structural reduction (shrinking and compaction) processes correspond to the same reaction: the injection of electrons and expulsion of counterions with two different kinetics imposed by two reaction-induced 3D structures (swollen or closed and rising packed) in the film.

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