Electrochemical behaviour, chronocoulometric and kinetic study of the redox mechanism of polyaniline deposits

Abstract Polyaniline (PANi) is prepared electrochemically in the acid eutectic mixture NH4F+2.35 HF (PANi-F), in aqueous sulfuric medium at different pH (PANi-S, or PANi-N if Na2SO4 is added). The number of electrons involved in the redox mechanism of PANi is measured by multiple potential step chronocoulometry (PSC). During the electropolymerization of aniline to PANi-F, the PSC technique shows that 0.60 to 0.75 e− per aniline ring are exchanged during the redox process of polymer. The reactions of several redox species on PANi-F, PANi-S and PANi-N coated electrodes are followed by cyclic voltammetry (CV). They are driven between −1.5 V and +1.0 V in aqueous and organic non-buffered media. The shape of these voltammograms indicates that, contrary to literature reports, PANi is conducting only in the oxidized state. The kinetics of the charge transfer and the cross reaction rate at the polymer/solution interface are estimated and measured by using Levich's direct and inverse criteria. The process is diffusion limited by the species in solution, up to 2000 rpm, since the limiting current values are proportional to the square root of the rotation rate of the electrode. In this rotation range PANi exhibits conducting behaviour similar to that of the platinum electrode. Above 2000 rpm the process is probably charge-transfer limited at the polymer/solution interface and in the polymeric bulk. The electron cross reaction rate at the polymer/solution interface is found to be Kcross=1.5 to 2×107 cm mol−1s−1.