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

Abstract

Many aspects of the conduction mechanism and the electrochemical switching of arylamine-derived polymers are still under discussion. 1,2 Although a variety of techniques has been applied to the study of these problems, the effect of temperature has received little attention. [3][4][5][6][7][8] On the other hand, electrochemical impedance spectroscopy (EIS) has proved to be a powerful technique for studing the electrochemical behavior of this kind of polymers. Several impedance studies of poly(aniline) (PANI) have contributed 3,[9][10][11][12][13][14] to the present understanding of the charge-transport processes in this type of polymers. Recently, we have applied EIS to study the response of poly(otoluidine) (POT), [15][16][17][18][19] in both the insulating (reduced) 20 and the conducting (half-oxidized) 21 states; as well as to the insulator-conducting transition. 21 There, it is concluded that in the reduced state the conductivity at very high frequencies is independent of the conductivity of the bathing electrolyte and cannot be explained by the sole contribution of the solution within the polymer pores. Also, in the reduced state, the EIS response, which is characterized by a big semicircle, is due to ionic charge transfer across the polymer-solution interface. 20 On the other hand, in the conducting state, the high-frequency conductivity of the polymer is very high whereas at low frequencies it is lower and is controlled by the diffusion of anions in the polymer. 21 The conductivity of PANI has been studied as a function of temperature by Inzelt et al., 3 in the range 296 to 324 K, with the aim of differentiating the conceivable conduction mechanisms. Among other things it was found that the conductivity increases as the temperature rises. Moreover, in a recent paper 22 it has been reported that the in situ conductivity of PANI was found to increase in the range 278 to 348 K.Here, we show the impedance response of POT in 3.7 M H 2 SO 4 , as a function of temperature, in the range 218 to 293 K. Since we were interested in the insulator-conductor transition and in the properties of the insulating and conducting states, we have studied only the potential region corresponding to the first oxidation peak, in our case the range going from 0.0 to 0.6 V. ExperimentalThe POT films were built up on Au electrodes by electropolymerization of the monomer at room temperature, from 0.65 M o-toluidine ϩ 1.5 M H 2 SO 4 ϩ 1.5 M HClO 4 solution, by continuously cycling the potential at 0.1 V s Ϫ1 , between 0.15 and 0.95 V vs. reference hydrogen electrode (RHE). 19 The film thicknesses were derived from the voltammetric charges in free monomer electrolyte (Q ϭ 13 mC cm Ϫ2 ). On the basis of the relationship between the reduction charge and the film thickness, which was previously established by ellipsometry for similar polymers, 23,24 the polymer thickness is about 62 nm. The electrolyte solutions were prepared from H 2 SO 4 (97%), HClO 4 (70%) acids [Merck, purified agent (p.a.)], o-toluidine (Fluka-Garantie, puriss. p.a.), a...

pH dependence of the voltammetric response of Polyaniline

“…The base electrodes were gold wires 2 cm long and of 0.5 mm radius. Pani films were obtained by electro polymerization on Au electrodes [15,16]. The electrosynthesis were carried out by cycling the potential at 0.10 V s −1 between − 0.20 V vs. SCE and a positive potential limit set at the beginning of the monomer oxidation (around 0.70-0.80 V).…”

“…To improve the adherence and homogeneity of the film, after a few cycles, the positive potential limit was slightly decreased. A conventional three electrode glass cell was employed [15,16]. After the synthesis, the films were washed with pure water and cycled in 3.7 M H 2 SO 4 solution, until the stationary voltammetric profile is achieved.…”

Temperature Effects on the Relaxation of Poly(aniline) and Poly(o-toluidine)

“…Thus, in the whole field of conducting polymers, only a few works on changing this variable have been reported. 13,[27][28][29][30][31][32] To our knowledge, no studies of the temperature dependence of the relaxation phenomena have been reported. Therefore, we think that more insight on the relaxation effect can be obtained from the study of its the temperature dependence.…”

Manipulation of polymer layer characteristics by electrochemical polymerization from mixtures of aniline and ortho‐phenylenediamine monomers

“…However, the obtained high resistances of R 1 and R 2 are characteristic of a nonconductive polymer layer. In the literature, it usually includes resistance of polymer layer, and resistance of pores within the polymer that are filled with electrolyte 23, 24. Because PANI1‐OPDA5 shows higher resistance values compared to PANI1, the size of pores and the amount of the solution within the pores should therefore be smaller in the case of PANI1‐OPDA5 (i.e., the layer is more compact).…”