The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

Abstract

There are several types of aniline oligomers that can be formed in the early stages of aniline oxidation: linear oligomers with repeating units joined in para positions, and various branched and polycyclic oligomers, being the two most important groups. The fraction of these different oligomeric groups depends upon the reaction conditions of aniline oxidation. The aim of this study was to analyze the first products of the chemical and electrochemical oxidation of aniline at the (starting) pH 1 and 7, in order to specify the conditions of the formation of phenazine-like oligomers, and to test the theory that they have an important role in polyaniline film formation. We have confirmed that phenazine-like oligomers do not form at pH 1, neither in the chemical nor the electrochemical oxidation of aniline; however, they form in both chemical and electrochemical oxidation of aniline at pH 7. Phenazine-like oligomers are thus definitely not necessary intermediates for PANI film formation, not even in the chemical polymerization of aniline. Finally, the redox behavior of phenazine-like oligomers was demonstrated in a medium at pH 1.

Performance Improvement of Gold Electrode towards Methanol Electrooxidation in Akaline Medium: Enhanced Current Density Achieved with Poly(aniline-co-2-hydroxyaniline) Coating at Low Overpotential

“…The CV curves recorded with the oxidation of monomers of aniline, 2-hydroxyaniline, and their mixture are shown in Figure S1. There is only one oxidation peak observed at 1.0 V on the forward scan of the CV curve recorded in aniline solution corresponding to the oxidation of amino group of aniline monomers (Figure S1a) in accordance with the previously reported data [37,38]. Two oxidation peaks at 0.67 V and 0.95 V are observed on the forward scan of the CV curve recorded in 2-hydroxyaniline solution (Figure S1b).…”

“…Figure 2 shows the CV curve of a PACHA coated electrode in monomer free electrolyte solution. It displays polyaniline-like electrochemical features as displayed in Figure S2 where two redox processes are clearly observed, as reported elsewhere [37,38]. The anodic peak around 0.26 V corresponds to the transformation of the leucoemeraldine form of the polymer to an emeraldine state, whereas the peak at 0.70 V corresponds to further transformation of the emeraldine form to a pernigraniline state.…”

“…The anodic peak current was found to increase with the increase in scan rate from 25 mV/s to 200 mV/s, indicating that the methanol oxidation reaction at the PACHA coated electrode attained good stability with the increase in scan rate [59]. A slight shift in peak potentials is observed with the increase in scan rate, indicating contribution from electrochemical polarization and kinetics constraints of methanol oxidation on PACHA modified gold electrodes [38,60,61]. The electrooxidation of species at the electrode surfaces are either adsorption controlled or diffusion controlled.…”

Enhanced Chemical and Electrochemical Stability of Polyaniline-Based Layer-by-Layer Films

“…All recorded spectra included the characteristic peaks of PANI. As summarized in Table 1 , the peaks at ~1590 cm −1 and ~1500 cm −1 are attributed to the -C=C- stretching of the quinoid (Q) ring and benzenoid (B) ring, respectively [ 34 ]. The peaks ~1310 cm −1 and ~1160 cm −1 are ascribed to the C-N vibration of secondary aromatic amine and -NH + vibration from the protonation of nitrogen atoms in the imine ring of quinone, while the peak at ~820 cm −1 is attributed to the trans =C-H out-of-plane bending [ 35 , 36 ].…”

Electrochemical Soft Actuator: Deciphering the Difference in the Characteristics of Polaronic and Bipolaronic Forms of Polyaniline

“…A broad band around 1364 cm –1 corresponds to ν C–N of the localized polaron in the phenazine-like structure and the Raman band around 1610 cm –1 corresponds to ν C–C stretching of the benzenoid-type ring (Figure S9a, Supporting Information). , Bands centered around 1480 and 1590 cm –1 correspond to ν CN and CC present in the quinoid-like structure (Figure S9b, Supporting Information), again confirming the formation of the bipolaronic form under open barrier conditions. The Raman bands observed at 1167 and 1188 cm –1 for the polyaniline polymerized at intermediate surface pressures of 3 and 8 mN m –1 (Figure S10, Supporting Information) reflect the presence of both the polaronic and bipolaronic forms.…”