M.I. Florit

Electropolymerization of 2-methoxy aniline. Electrochemical and spectroscopical product characterization

Poly(2-methoxyaniline) (PMOA) was electrosynthesized with varying monomer concentrations in 1 M HClO4. The polymers obtained were characterized using cyclic voltammetry, Fourier transform IR diffuse reflectance spectroscopy (FTIR-DRS), UV–vis spectroscopy and electrochemical impedance. At relatively high monomer concentrations (>20 mM), the polymer obtained is similar to aryl amine conducting polymers, but shows in its voltammogram an intermediate peak, which becomes larger as the monomer concentration decreases. For monomer concentrations below ∼20 mM, the polymer becomes more resistive, behaving similarly to aryl amine redox polymers. The different techniques employed show results consistent with the voltammetric experiments. This change of behaviour indicates that different polymers are obtained as the monomer concentration is modified.

Voltammetric study of the reduction and relaxation of poly(o-toluidine). Effect of the polymer thickness and the external electrolyte nature and concentration

The reduction and relaxation of poly(o-toluidine) (POT) was studied as a function of the wait time at different waiting potentials near the reduction potential of the polymer. The influence of the film thickness, the acid concentration, and the ionic strength of the external electrolytic solution on these processes were also studied. Two types of electrolytes were employed: perchloric and sulfuric acid. Both the reduction and the relaxation times depend on the proton concentration of the external electrolyte media and on the film thickness. They are independent of the ionic strength and, in a limited range, of the waiting potential. The voltammetric response of fully reduced and relaxed polymers shows that, at low sweep rates, the kinetics are controlled by slow ionic movements within the polymer. Experiments with medium exchange show that, once the polymer is fully reduced and relaxed, its state is independent of the composition and concentration of the electrolyte in which this particular state was obtained. Furthermore, they also show that the shape of the voltammetric oxidation profile depends exclusively on the composition and concentration of the electrolyte in which the polymer is being oxidized. This means that the effect of the solution composition and concentration is manifested only through the participation of protons and anions in the mechanism of oxidation of the polymer.

IR response of poly-(o-toluidine) : spectral modifications upon redox state change

The IR spectra of poly(o-toluidine) in the reduced, half and fully oxidized states have been studied in both salt and base forms. The bands in the range 1500 to 1600cm−1 undergo important intensity changes as the degree of oxidation increases. The IR spectra show that during the electrochemical polymerization there is an influence of the nature of the anion present in the electrolyte. This shows up as conformational differences in the polymer backbone, but it does not affect the chemical structure. Also, spectral changes are observed when the polymer is oxidized in supporting electrolytes containing different anions. This has been interpreted by considering that the less hydrated anions can approach closer to the positive centres of the protonated amine groups.

The potentiodynamic behaviour of iridium electrodes in aqueous 3.7 M H2SO4 in the 293–195 K range

Abstract The effect of temperature on the potentiodynamic behaviour of Ir in 3.7 M H 2 SO 4 was studied in the range 293–195 K. At 293 K, voltammograms are close to those reported for Ir in dilute acids, but no activation for hydrous oxide growth was observed. The H atom potential range exhibits weakly and strongly bound H adatom species. Slow and fast kinetic contributions can be distinguished by applying conventional and triangular modulated voltammetry, respectively. The weakly H adatom electrosorption reactions behave as reversible processes even in the frozen electrolyte while the kinetics of strongly bound species is influenced by a competitive adsorption probably involving sulphate ions. This effect becomes more remarkable as the temperature is diminished. Reversible processes involving H adatom and O-containing species in Ir oxide layers are explained in terms of fast charge transfer accompanied by fast proton motion processes at the interface.

Apparent formal redox potential distribution in electroactive arylamine-derived polymers

Abstract The concept of distributed formal redox potentials is employed to analyse and study the i / E response of different arylamine-derived polymers, poly- o -aminophenol (POAP), poly- o -phenylenediamine (POPD) and polybenzidine (PBZ), and a conducting polymer, poly- o- toluidine (POT), in different electrolytic media. The analysis of the experimental data allows determining the formal redox potential distribution. The experimental formal redox potential distributions are interpreted on the basis of a simple statistical thermodynamic model that considers the possibility of expansions and contractions during the oxidation–reduction cycles applied to the polymer. It is considered that units having several redox centres constitute the polymers and that these units change in size during the oxidation–reduction cycles. The analysis of the experimental formal redox potential distribution allows obtaining the number of redox centres per polymer unit, the ratio of the internal partition function of the units and the formal redox potential of the centres. These results are in agreement with the previous studies on the electrochemical behaviour of these polymers.

The Effect of Temperature on the Impedance of Poly‐o‐toluidine in 3.7 M H 2 SO 4

The impedance response of poly(o-toluidine) (POT) electrochemically grown films was investigated in sulfuric acid 3.7 M, in the temperature range 218 to 293 K. The Nyquist diagrams as a function of temperature show that the transition potential from the nonconductive to the conductive state shifts in the positive potential direction as the temperature decreases. This implies that, at low temperatures, a greater field is needed to induce the transition. In the nonconductive state both the high-frequency and the low-frequency resistances increase as the temperature is decreased. The Arrhenius plots for both show a break at about 255 K. This is in agreement with the fact that the high-frequency resistance is controlled by ionic movements and that there is charge-transfer control at the polymer/solution interface. In the conductive state the low-frequency capacitance is independent of temperature, showing that the active site concentration does not depend on the temperature. The low-frequency resistance in this potential region also depends on the temperature. No break is observed in the Arrhenius plot for this quantity. However from its slope it is inferred that ionic motions within the polymer control the charge transport in this state.

Proton Exchange during the Redox Switching of Polyaniline Film Electrodes

Proton ejection/injection during the redox switching of polyaniline (PANI) have been qualitatively measured employing the rotating ring-disk electrode in the amperometric mode at the ring. The ring response shows that there is proton ejection during the oxidation of a fully relaxed polymer both from the leucoemeraldine to emeraldine forms and from it to the fully oxidized form. During the reduction of the polymer there is proton injection. However, this process is incomplete for the emeraldine/leucoemeraldine transition, indicating proton equilibration is a slow process. The ring response during the second positive half-potential sweep (nonrelaxed polymer) shows that the ring current is much smaller, indicating the polymer is not in protonic equilibrium with the external electrolytic phase.

Electropolymerization of 2-methoxyaniline. Polymerization kinetics and phenazine insertion at low monomer concentrationElectronic supplementary information (ESI) available: Cyclic voltammograms. See http://www.rsc.org/suppdata/cp/b1/b110705d/

The electropolymerization of 2-methoxyaniline (MOA) has been found to yield products having structure and properties dependent on the monomer concentration, with the insertion of phenazinic units giving a redox-type polymer at low concentrations. The kinetics of this process is studied in 1 M HClO4 solutions containing different monomer concentrations. The voltammetric results are compared with the electropolymerization, in similar experimental conditions, of other aryl amines such as aniline and 2-methylaniline. The effect of dimeric additives on the polymerization rate of MOA is also studied. A change in the kinetic behavior is found at MOA concentrations of about 30–60 mM. An electropolymerization mechanism for 2-methoxyaniline is proposed through a reaction scheme similar to that of aniline, with the inclusion of a step consisting in a head-to-head coupling of oligomers and/or polymer chains yielding phenazine-type units, that effectively works as a termination step. The resistivity increase, in the conductive state, due to the insertion of redox units is also considered. The experimental results are interpreted on the basis of this mechanism.

Charge transfer in poly(o-toluidine) gold modified electrodes. An EIS study of the reduced state

The impedance response of poly(o-toluidine) (POT) electrochemically grown films was studied in the potential range, 0.0<E<0.35 V, where the polymer is in the insulating state. The electrolytes employed were aqueous solutions of H2SO4 and HClO4 with different concentrations. The predominant impedance parameters in this potential range, the charge transfer resistance, RCT, in parallel with the corresponding double layer capacitance, Cdl, were considered in terms of the applied potential, the polymer film thickness and the nature and concentration of the electrolyte.

Effect of Temperature on the Voltammetric Behavior of Poly‐o‐toluidine

The voltammetric response of poly(o-toluidine) electrochemically grown films of about 62 nm thick was investigated in the temperature range 218-293 K, using 3.7 M sulfuric acid. The peak current, i p , corresponding to the first oxidation process decreases with temperature. The peak current depends linearly on the sweep rate at all temperatures. At about 260-270 K, a discontinuity in the i p vs. T plot is observed. The peak potential for the anodic sweep shifts in the positive direction as the temperature is decreased and the full peak width at half-maximum, E w , increases as temperature is decreased. On the other hand, for the cathodic sweep, the peak potential just slightly shifts in the positive direction, and E w does not change as the temperature is decreased. In strongly acidic H 2 SO 4 solutions, the voltammetric capacity, i p v -1 , is found to be dependent on anion concentration rather than on pH. The temperature dependence of the voltammetric response is explained on the basis that the oxidation process is controlled by ionic movements into the polymer. As the temperature decreases, ionic movements become hindered and a decrease of the polymer voltammetric capacitive current, associated to the redox process, occurs