Analytical Sciences

Observation of Electrochemical Formation andDegradation Processes of Polyaniline by Fourier-Transform InfraredSpectroscopy

Masaharu NAKAYAMA, Seigo SAEKIand Kotaro OGURA *

Department of AppliedChemistry, Yamaguchi University, 2557 Tokiwadai, Ube 755-8611, Japan

The electrochemical polymerization of aniline on aplatinum electrode in aqueous HClO₄ andH₂SO₄ solutions has been studied by means of insitu Fourier-transform infrared (FTIR) reflection spectroscopy. Thespectra, taken at early stage of the polymerization in both solutions,exhibited the absorption characteristic of polyaniline (PAn) in anemeraldine state, even at a highly positive potential ( > =+0.7 V vs.Ag/AgCl (saturated KCl)). Polymer growth in H₂SO₄was accompanied by an increase in the molar ratio of[HSO₄-]/[SO₄^2-], indicatingthat the protons generated during the oxidation of aniline react withSO₄^2- to afford HSO₄^-, and thatpolymer growth is facilitated. In contrast, such proton-scavenging behaviorwas not observed in a HClO₄ solution, and the growth of PAn wassuppressed owing to the accumulation of protons. Under the condition thataniline was extremely consumed, the produced PAn was subjected to oxidativedegradation, which was competitive with the growth process of PAn. Themajor degradation species was identified to be p-benzoquinone. (Keywords: in situ Fourier-transform infrared, polyaniline,polymerization, degradation, p-benzoquinone)

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