Electrochemical in situ epr evidence of two polaron-bipolaron states in polyaniline

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Abstract

An in situ EPR experiment during cyclic voltammetry of a polyaniline (PANi) film made in NH4F+2.3 HF medium provided evidence that two polaron states are created for the two electrontransfer reactions that are very well discriminated in such a medium. The results were used to support a new redox mechanism for the electrochemical behaviour of polyaniline. We propose that during the first electron-transfer reaction some of the nitrogen atoms are transformed from the amine to the imine form, and during the second reaction, the oxidation of the imine form to a new conjugated polycationic polymer takes place. The EPR signal indicated that the g value of the second polaron was lower than that of the first one. The mechanisms are discussed with regard to results in the literature and also to in situ EPR experiments on polyaniline made in NH4F+2.3 HF and cycled in sulphuric acid, or made in sulphuric acid and cycled in NH4F+2.3 HF or sulphuric acid.

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