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Redox mechanism and electrochemical behaviour or polyaniline deposits

1985; Elsevier BV; Volume: 195; Issue: 1 Linguagem: Inglês

10.1016/0022-0728(85)80009-7

2590-2954

E.M. Geniès, C. Tsintavis,

Analytical Chemistry and Sensors

Polyaniline (PANi) is prepared electrochemically by anodic oxidation of aniline in the eutectic mixture NH4F, 2.35 HF (PANi-F), in aqueous sulfuric medium at different pH (PANi-S), or (PANi-N) if Na2SO4 is added. Thin deposits of PANi-F, prepared by potential step or sweeping, have a compact form at all aniline concentrations, with almost 100% polymerization yield and a strong adherence to the electrode. Thin deposits of PANi-N and PANi-S have identical characteristics, but only when prepared by potential sweeping at low aniline concentration. When the deposits are thick, only PANi-F displays these interesting properties, giving hard fibres, which adhere strongly to the electrode as the polymerization proceeds. Prepared with equal amounts of charge samples, a higher charge and discharge capacity is measured (coulombs) for PANi-F deposits than for PANi-N and PANi-S. Only PANi-F exhibits a faradaīc yield close to 1 after 2000 cycles. Observations on the electrochemical behaviour of PANi suggest a redox mechanism involving a proton + electron exchange and a doping process with ion insertion. The cyclic voltammograms obtained with PANi—coated electrodes show two or three rapid, reversible and clearly defined electrochemical systems. The second electrochemical system (2,2′) is obtained during the oxidation of aniline at higher potentials than those needed for the first (1,1′) and the third (3,3′) system. Therefore, a different structure of polymer may be associated with system 2,2′ than the para-coupling structure attributed to the systems 1,1′ and 3,3′. The polymerization of p-fluoraniline is possible (+0.72 V) at the same potential as aniline (+0.7 V). Hence, the participation of the ortho positions in the electropolymerization mechanism of aniline is a possibility to take into consideration. The cyclic voltammograms recorded during the electrodeposition of N-phenyl p-phenylenediamine, exhibit a similar form as those recorded for PANi-F. Therefore, it is confirmed that the polymerization of aniline proceeds through a head-to-tail coupling of cation radical.