Estimation of Equilibrium Capacitance of Polyaniline Films Using Step Voltammetry

Synthetic Metals, 1993

The electrochemical ionic exchange of polyaniline film-coated electrodes was studied in detail by electrogravimetry using an electrochemical quartz crystal microbalance. The influence of film thickness, electrolyte composition and potential sweep rate is discussed. The data obtained from these measurements establish the dependence of ion population inside the film on the degree of oxidation from -0.25 to 0.5 V (versus SCE). Analysis is made by calculating the relative contribution of anions and cations to the polymer electroneutrality from the electrochemical quartz crystal microbalance and electric charge data.

1999

Characterization of polyaniline (PANI) by electrochemical and spectroscopic techniques are presented. The electrochemical investigation reveals the influence of the dopant acid on the kinetic parameters of polyaniline films: exchange current density (I 0) and the cathodic transfer coefficient (α c). UV-Vis spectra of thin films of polyaniline in N-metil pyrrolidine solutions indicate the increase of the absorbance with the number of deposition cycles, N. The inhibition of polymer degradation in thick films was confirmed by these spectra.

2005

Polyaniline (PANI) films have been deposited on stainless steel (SS) substrate by galvanostatic, potentiostatic and potentiodynamic methods. Electrochemical impedance spectra of the electrodes have been analyzed using a transmission line model consisting of two rails of finite resistances. The impedance spectra of the galvanostatically prepared electrodes are similar in shape to those of potentiostatically grown electrodes. The resistance of aqueous pore (R aq) due to ionic doping-dedoping process is greater than the resistance (R p) of electronic chargetransfer on polymer chain. These parameters exhibit an increase in magnitude with thickness of PANI, as expected from the transmission line theory. The shape of impedance spectra of potentiodynamically grown PANI, however, is different and its R aq ≤ R p. The impedance parameters of potentiodynamically prepared PANI/SS electrodes have been found to depend on the sweep rate used for the deposition of PANI. Several possible explanations have been discussed to understand the influence of sweep rate during deposition on impedance parameters of the electrodes. In contrast to the behavior of PANI deposited by galvanostatic and potentiostatic methods, R p decreases with an increase in thickness of PANI deposited by the potentiodynamic method. The effect of concentration of aniline used for the deposition of PANI on impedance parameters has also been studied. The results of capacitance of PANI obtained from the ac impedance studies have been found to be comparable with those obtained from the cyclic voltammetric studies.

Journal of The Electrochemical Society, 1999

Relaxation phenomena in thin polyaniline films synthesized chemically and electrochemically are investigated by UV-vis and IR spectroscopy. It is shown that the relaxation process carried out from the electrochemically oxidized or electrochemically reduced states of the polyaniline always proceeds toward the emeraldine state. The relaxation process in acid is governed by disproportionation and formation of semiquinone radicals. The changes in the population density of the polaronic states within the polaronic band allows determination of the change in the oxidation state and consequently the change in the position of the Fermi energy level. The formation of polaronic states is ascertained by diffusion of ions from or into t h e polyaniline matrix in solution and * To whom correspondence should be addressed.

Synthetic Metals, 2002

Polyaniline (PANI) ®lms were electrodeposited on Pt electrode by cyclic voltammetry using an anodic switching potential of 0.90 V, which favored benzoquinone (BQ) as side product. The redox interactions between BQ and PANI were analyzed through electrochemical impedance spectroscopy (EIS). PANI ®lms of different thickness were subjected to different applied potentials and impedance spectra were recorded. PANI ®lms were found to show negative capacitance (inductive loop) in the potential range of 0.50±0.70 V. A redox mechanism involving the role of BQ to impart negative capacitance to PANI is given and supported by the results from X-ray photoelectron spectroscopy (XPS). An equivalent circuit including an inductor element (L) is found to ®t perfectly with data from EIS. The effect of thickness of PANI on L-value is elucidated and discussed. #

International Journal of Chemistry, 2018

The double layer capacitance of polyaniline (PANi)-coated electrode in acidic solution exhibited little frequency dispersion under the emeraldine (electrically conducting) state, while it showed large frequency dispersion under the insulating state. The former has a possibility of working as such an ideal capacitor that it may generate neither heat in iterative charge-discharge processes nor leakage of stored charge. The frequency dispersion is generally expressed by f-l for ac-frequency f and a constant l. This power law is ascribed to orientation of solvent dipoles rather than non-uniform distribution of ions. The value of l under the conducting state was close to zero, implying the orientation to be facilitated by less interaction of solvents. The less interaction was supported indirectly with strain-stress curves of PANi by atomic force microscopy. l-Values close to zero were retained even for thick PANi films.

Journal of Solid State Electrochemistry, 2019

In the present work, we review the occurrence of capacitive currents in conducting polymer and, particularly, in the electrochemical response of polyaniline film-coated electrodes Firstly, we present and discuss the differences between the electrical double-layer capacitance and the so-called pseudocapacitance. Then, we discuss the capacitive behavior of Pani as studied by a variety of electrochemical (cyclic voltammetry, electrochemical impedance spectroscopy) and spectroscopic techniques (epr, UV-visible). Understanding the capacitive behavior of polyaniline (Pani) becomes essential not only from an academic point-of-view but also from a technological perspective, as Pani has been extensively employed for the construction of materials for supercapacitors.

Journal of Non-Crystalline Solids, 2010

The effect of temperature on the electrochemical oxidative polymerization of aniline and on the electrochemical properties of the resulting polyaniline (PANI) film was studied. The electrochemical deposition of PANI has been carried out on platinum at different temperatures. Three different films (PANI-25, PANI-40 and PANI-60) have been prepared at 25, 40 and 60°C by electrochemical polymerization and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Increasing the synthesis temperature leads to an increase of the polyaniline films thickness from 0.4 to 0.9 lm and, respectively, 1.1 lm, associated with an increase of the films capacitances from 3 Â 10 À2 F cm À2 to 7 Â 10 À2 F cm À2 and 10 Â 10 À2 F cm À2 . The impedance measurements showed that only PANI-25 and PANI-40 exist in the conductive state over a large potential window, while PANI-60 has an intermediate behavior at low and high electrode potentials.

The Journal of Physical Chemistry B, 1999

A detailed investigation of the acid doping behavior of polyaniline has led to a robust and reproducible procedure for controlled adjustment of the redox state of dry polyaniline films. The initial step in this procedure is the casting of PANI films from formic acid. The subsequent exchange of the trapped formic acid for other primary dopants obtained from mono-and polyprotic acids (e.g., CH 3 COO-, BF 4-, HSO 4-, SO 4 2-, H 2 PO 4-, and HPO 4 2-) is demonstrated. The voltammetric and the spectroscopic behavior of the PANI doped with different anions indicate that both the protons and the anions of dopant acids influence the structure and redox properties of the polymer. The redox state of PANI doped with homologous series of chloroacetic and carboxylic acids correlates with the pK a of the dopant acid. These results show that it is possible to prepare the polymer with a desired oxidation state according to the pK a of the dopant acid of a given homologous series. The exchange of the formic acid for both stronger and weaker doping acid can be repeatedly accomplished by electrochemical cycling.

Electrochimica Acta, 2010

Mobile counter anion exchange of electropolymerized polyaniline (PANI) films with the anions in acid solutions has been investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy, Raman, UV-vis, and fluorescence spectra. The studied acids include camphorsulfonic acid, p-toluene sulfonic acid, HCl, HClO 4 , H 2 SO 4 and H 3 PO 4. In two cases of small and large counter ions of PANI films, CV tests have been performed alternately three times in each of two electrolytes containing organic or inorganic acid. The investigation of electrochemical and spectrophotometric measurements reveals that large counter anions can be easily replaced by the small anions; and the reverse exchange also occurs, but shows very low efficiency. This indicates that the achieved anion exchange in both cases leads to the remarkable alteration in electrochemical behavior and electrical conductance of PANI films. This implies counter anions, whatever the original or redoping ones, play an important role in the electrical, electrochemical, even optical properties of PANI. However, the polymer morphology does not be changed after exchange tests. This allows us to point out a 'morphologymemory' effect which is very significant for the development and application of PANI films with the same morphology and different properties.

Energies, 2022

We report on the formation of semi-polycrystalline polyaniline, a novel electroactive polymeric material synthesized by a modified surfactant-free chemical route and its enhanced electrochemical capacitive behavior. The material exhibits uniformly arranged spindle-shaped morphology in scanning electron microscopy and well-defined crystallographic lattices in the highresolution transmission electron microscopy images. The X-ray diffraction spectrum reveals sharp peaks characteristic of a crystalline material. The characteristic chemical properties of polyaniline are recorded using Fourier transform infrared technology and laser Raman spectroscopies. The cyclic voltammetry curves exhibit features of surface-redox pseudocapacitance. The specific capacitance calculated for the material is 551 F g􀀀1 at a scan rate of 10 mV s􀀀1. The cycle stability and the coulombic efficiency recorded at a current density of 12 A g􀀀1 exhibited good stability (90.3% and 99.5%, respectively) over 3000 cycles. Keywords: polyaniline; semi-polycrystalline polyaniline; electroactive material; electrochemical capacitor; pseudocapacitor; galvanostatic charge–discharge (GCD) 1. IntroductionThis article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

The Journal of Physical Chemistry, 1985

S LC Reproduction in whole or in part is permitted for Lii any purpose of the United States Government. This document has been approved for public release Cand sale; its distribution is unlimited.

Journal of Taibah University for Science, 2014

In this report, we investigate the electrochemical capacitance and redox behaviour of a stand-alone polyaniline-poly(vinyl alcohol) composite film cast on an insulating substrate (normal printer paper) and compared it with an electrochemically synthesized composite film deposited on a gold electrode. The stand-alone composite film showed timescale-dependent, wide range charging-discharging redox cycling and high electrochemical capacitance in potentiodynamic electrochemical experiments carried out in 1 M HCl solution.

European polymer …, 1997

Capacitors with Al-pani (CH 3 SO 3 H)-Al sandwich film structure were fabricated. The top and bottom aluminium electrodes were deposited by vacuum evaporation and the pani (CH 3 SO 3 H) film deposited by a solution casting method. An X-ray diffractogram indicates the ...

Synthetic Metals, 1998

A systematic investigation of the redox properties of polyaniline in aqueous solutions using the capacitance-potential curves was done. The variation of the capacitance values in different regions of the sweep potentials was associated with the charge transport and the Ž capacitive processes in the polymeric film. An increase in the capacitance was observed in the region of the first redox process 0.1 to 0.6 . y V , which is associated with the charge accumulation in the film due to the polymer oxidation and the Cl intercalation. In the third Ž . q redox process in the voltammograms 0.85 to 1.2 V , a decrease in capacitance was observed which could be related to the H deintercalation and the formation of the pernigraniline state.