Fuzzy nanofibrous network of polyaniline electrode for supercapacitor application

Fuzzy nanofibrous network of polyaniline electrode is successfully electrosynthesized for supercapacitor application. The nanofibre network of polyaniline electrode is characterized using Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM) and optical absorption studies. Network of polyaniline is highly porous with interconnected fuzzy nanofibres having diameter typically between 120 and 125 nm. The supercapacitive performance of polyaniline electrode is tested using cyclic voltammetry (C-V) technique in H₂SO₄ electrolyte within potential range of ?100 to 800 mV. The effect of scan rate on the capacitance of polyaniline electrode is studied. The highest specific capacitance of 839 F g^?1 at the voltage scan rate of 10 mV s^?1 is achieved. Additionally stability and charging–discharging of polyaniline electrode are studied.     

The reduction of silver nitrate to metallic silver inside polyaniline nanotubes and on oligoaniline microspheres

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm^?1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10^?5 S cm^?1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.     

The reduction of CO2 on polyaniline electrode in a membrane cell

Electrochemical reduction of CO₂ has been investigated on polyaniline (PAn) electrode at −0.4 V_SCE in a Nafion^® 417 membrane cell at ambient conditions by using methanol as a solvent. As reaction product has been found formic acid and acetic acid. The maximum Faradaic efficiencies of the products were found to be 12% for formic acid and 78% for acetic acid.     

Aluminum as a suitable substrate for the deposition of conducting polymers: application to polyaniline and enzyme-modified electrode

Electrochemical polymerization of aniline onto an aluminum substrate electrode was studied. The obtained results were compared to those obtained with Pt substrate electrode. It indicates the possibility of aluminum for using as substrate electrode for electropolymerization. Moreover, the electrochemical polymerization of aniline on a passivated Al electrode was studied. The stability of the three different electrodes were studied and compared during potential cycling. Incorporation of glucose oxidase as a typical enzyme into the polymer films was investigated to prepare an enzyme-modified electrode. The activity of the enzyme incorporated into the polyaniline films formed on different substrate electrodes was also discussed.     

Electrochemical oxidation of dissolved carbon monoxide on gold electrode in alkaline medium

The study of the oxidation of dissolved CO is not much seen in the literature probably due to the strong adsorption of CO on platinum metals in acidic media. This work was thus undertaken to study the electrochemical oxidation of dissolved CO on Au in alkaline medium without the influence of adsorbed CO. Our results show that the electrochemical oxidation of dissolved CO on gold electrode is mainly diffusion-controlled process at the potential greater than 0.3V (vs. RHE). At the potential range between 0.0V and 0.3V, the oxidation process is a mixed-control process. Our data also confirm that the electrochemical oxidation of dissolved CO is affected by the presence of surface oxide on gold. The electrochemical oxidation of the dissolved CO at liquid-solid interface may provide certain practical uses in CO removal or low temperature fuel cell.     

Impedance analysis of polyaniline prepared on interdigitated array electrode under direct current polarization potential

A new method, ‘biased impedance analysis (BIA)’, was proposed for in situ measurements of a.c. impedance of polyaniline (PAn) film during and after deposition on an interdigitated array (IDA) electrode under d.c. bias (polarization) potential. With this BIA we designed two types of experiments: one was BIA under cyclic voltammetric (CV) sweep in 1 M HCl on PAn films polymerized via a constant current (40 μA cm⁻²) mode in properly buffered media at different pH (below 1.7) but with the same chloride ion concentration ([Cl⁻] = 1 M); the other was BIA on PAn films during and after constant potential (+ 0.75 V) mode polymerization in 1 M HCl or 1 M HClO₄ both at pH = 0.2. As to the effect of pH of the polymerization media, the PAn film obtained at high pH had narrow conductive potential range during CV scans between −0.1 and 1.0 V as compared with that obtained at low pH. The PAn film obtained in HClO₄ exhibited faster and larger impedance increase (than that polymerized in HCl), leading to a poorer performance upon potential scanning especially from the conductive-oxidation state at high potential to the insulating-reduction state at low potential.     

Kinetics and mechanism of the electrode reactions on iron in nitrate solutions

The anodic dissolution reaction of pure iron and the cathodic reduction of the nitrate ions on the active iron electrode in nitrate solutions have been studied by means of steady state and pulse polarization techniques. A mechanism of the nitrate ion reduction is proposed, which involves a charge transfer step, producing adsorbed hydrogen atoms, at quasi equilibrium with a subsequent rate-determiring electrochemical desorption step. The available data for the anodic dissolution reaction permit the assumption of a two-electron transfer rate-determining step.     

Understanding electrodeposition of polyaniline coatings for corrosion prevention applications using the wire beam electrode method

Polyaniline (PANI) films have been successfully electrodeposited on aluminium AA1100 electrode surfaces in acidic electrolytes as anti-corrosion coatings. The wire beam electrode (WBE) has been applied for the first time as a novel tool to monitor the electrodeposition processes; and also to understand the anti-corrosion performance and mechanism of the PANI coatings. During PANI electrodeposition, the WBE was polarised anodically, and anodic polarisation currents were measured from various locations over the WBE surface to produce anodic polarisation current maps (APC maps). Preliminary experiments have revealed that if an AA1100 electrode was not pre-treated, APC maps would show a localised anodic current distribution, resulting in a nonuniform PANI deposit. If the AA1100 electrode was pre-treated by a cathodic polarisation process, APC maps would show a random anodic current distribution, leading to a PANI coating covering the whole electrode surface. When exposed to a corrosive environment, PANI coatings were found to prevent localised corrosion of AA1100, primarily by enhancing its passive film rather than by a barrier mechanism. However, a nonuniform PANI coating has been found to accelerate general corrosion of AA1100. These results suggest that the WBE is a practical tool for monitoring, characterising and optimising PANI electrodeposition processes and for evaluating the anti-corrosion performance of PANI coatings.     

Electrochemical and physical characterization of lithium ionic salt doped polyaniline as a polymer electrode of lithium secondary battery

Polyaniline films doped with lithium ionic salts such as LiPF₆ and LiBF₄ were prepared by using the electrolyte solution mixture of ethylene carbonate and dimethyl carbonate. The doping level of the polyaniline films was confirmed by X-ray photoelectron spectroscopy and dc conductivity experiments. A doping mechanism of lithium ion through the interaction with a nitrogen at imine site is proposed. Electrochemical cells of Lipolyaniline-LiPF₆ or Lipolyaniline-LiBF₄ were assembled to investigate electrical capacity and its trends over the repeated charge/discharge cycles. The capacity of Lipolyaniline cell was increased and then saturated over 15 cycles. However, it did not reach the half of theoretical capacity of polyaniline material. The mechanism of electrochemical reaction during charge/discharge process of Lipolyaniline cell is presented.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

Investigation of polyaniline co-doped with Zn2+ and H+ as the electrode material for electrochemical supercapacitors

Polyaniline co-doped with Zn²⁺ and H⁺ was synthesized in aqueous HCl solution containing ZnCl₂, and tested for its supercapacitive behavior in three-electrode or two-electrode system with 1.0 M H₂SO₄ as electrolyte by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) techniques were employed for characterization of polyaniline co-doped with Zn²⁺ and H⁺. Compared with polyaniline doped with H⁺, it shows a larger specific capacitance of 369 F g^?1. Moreover, the specific capacitance remains 90% after 1000 cycles at a current density of 0.5 A g^?1, indicating good cycleability.     

Optical responses of polyaniline inverse opals to chemicals

Inverse opals are three-dimensionally ordered macroporous materials with properties important for sensor applications, such as high specific surface area and pore interconnectivity. The present paper investigates optical responses of polyaniline inverse opals to ethanol, hydrogen chloride, and ammonia, especially changes in the optical stop band originating from the structural periodicity. Examination by scanning electron microscopy shows that the chemically synthesized inverse opals were of good quality, and the stop band in reflectance spectra provides additional evidence of long-range order. When in ethanol vapor, the inverse opals had noticeable shifts in the stop band because of the swelling-induced dimension changes, as confirmed by atomic force microscopy. Moreover, hydrogen chloride and ammonia, both capable of varying the degree of protonation of polyaniline, significantly altered the refractive index and thus the stop band position; shifts of more than 100 nm were observed.     

The transient response of the copper electrode potential to elastic straining and its relation to the reaction kinetics

The potential of a copper electrode elastically strained in an acid aerated CUSO₄ solution displays a very characteristic, reproducible and reversible transient change. The shape and magnitude of the transients are closely related to the kinetics of the different reaction steps, as shown by impedance measurements, taken under the same conditions. It is shown that the analysis of the response may produce information equivalent to the impedance spectra. Consequently, elastic stressing may be used as a diagnostic tool in the investigation of the reaction kinetics particularly when adsorption is involved.     

A comparative study on polyaniline degradation by an electrochemical quartz crystal impedance system: electrode and solution effects

By combining the piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance spectroscopy (EIS) measurements, we conducted a comparative study on polyaniline (PANI) degradation in different media, HClO₄ and H₂SO₄, and on different piezoelectric quartz crystal (PQC) electrodes, Pt and Au. It is concluded that (1) the PANI film grown on an Au electrode is more stable than that on a Pt electrode; (2) the PANI degradation reaction abides by the zero-order kinetic law in HClO₄ with rate constants from 0.17 to 2.25 Hz s⁻¹ on Pt and 0.16 to 0.83 Hz s⁻¹ on Au, but the first-order kinetic law in H₂SO₄ with rate constants from 2.61×10⁻³ to 7.00×10⁻³ s⁻¹ on Pt and 1.00×10⁻³ to 5.00×10⁻³ s⁻¹ on Au at different ion concentrations. The contrary effects of ClO₄⁻ and SO₄²⁻ on PANI degradation may be understood from the Hofmeister series of anions; (3) the dissolution of the PANI film bulk, the increase of film porosity and the film attenuation occurred simultaneously during degradation via systematic analyses of the motional resistance (R₁)and electrochemical impedance spectra responses, etc.     

Geometry of polyaniline

In order to get a quantitative picture of the geometry of polyaniline, we have carried out MNDO calculations on segments of the polymer. The completely oxidized form (2A) shows an alternating benzoid-quinoid structure of the six-membered carbon rings, while the completely reduced form (1A) is all benzoid. The torsion angles between adjacent rings in the 2A and 1A forms are calculated to be 87° and 82°, respectively. In the protonated 2S′form the torsion angle between rings adjacent to a protonated nitrogen is reduced to ∼72°, while the torsion angle between rings adjacent to an unprotonated nitrogen is still close to 90°. The benzoid-quinoid structure is preserved in the 2S′ form and the charge transferred to the polymer chain is found to be well delocalized. We also present data from n.m.r. experiments on oxidized polyaniline before and after protonation. These data can be interpreted in a way consistent with the geometry obtained from the MNDO calculations. The n.m.r. spectrum of oxidized and protonated polyaniline is rather featureless, but the similarity in the distributions of chemical shifts between the spectra implies that the structure is unchanged upon protonation and that the injected charge is delocalized, i.e., in agreement with the MNDO results.     

The use of doped polyaniline as an electrode in the galvanic anodic protection of ferrous metals in industrial acid solutions

In order to investigate the galvanic anodic protection (GAP) of ferrous metals (such as 410, 304 and 316 stainless steels) in acid solutions by doped polyaniline (PANi), separate doped PANi powder-pressed electrodes with different surface areas (the area ratio of the PANi electrode to stainless steel is between 1:1 and 1:2) have been prepared. These were coupled with ferrous metal in the following solutions: 5 M sulphuric acid, 5 M phosphoric acid and industrial phosphoric acid (containing 5 M phosphoric acid and 0.05% chloride ion) to construct a galvanic cell, in which PANi is cathode while ferrous metal is anode. The results indicate that a PANi electrode with sufficient area can provide corrosion protection to stainless steel in these acidic solutions. A pilot scale coupling experiment was carried out. The results indicate that PANi is a promising material as an electrode for the anodic protection of ferrous metals in acidic solutions in industrial situations.     

The carbonization of granular polyaniline to produce nitrogen-containing carbon

Polyaniline (PANI) was prepared by the oxidative polymerization of aniline. The deprotonated product, a PANI base, was carbonized in an inert atmosphere at temperatures up to 800 °C for various times. The mass decreased to 40–50 wt.% at temperatures above 600 °C. The progress of molecular structure during carbonization was followed by infrared and Raman spectroscopies. The carbonization at 650 °C for 1 h is suggested for the optimum conversion of PANI to carbon. The product retained the original globular structure of PANI. The conductivity of the carbonized material was low for carbonizations below 600 °C, <10^?10 S cm^?1, and increased to 10^?4 S cm^?1 after treatment at 800 °C. The content of nitrogen, ～10 wt.%, was not affected appreciably by the carbonization.     

Mechanical properties of polyaniline

In spite of extensive electrical characterization of polyaniline, the information on its mechanical properties is missing in the literature. Complex Young's modulus of polyaniline compressed into pellets was measured at room temperature and an influence of preparation conditions of the polyaniline pellets on mechanical properties was studied. Young's modulus of PANI hydrochloride pellets was 0.9 ± 0.2 GPa and that of polyaniline base 1.3 ± 0.2 GPa. These values are comparable with common polymers, such as bulk polystyrene, 1.8 ± 0.1 GPa, or compressed polystyrene powder, 0.80 ± 0.02 GPa. Modulus of polyaniline is independent of the compression pressure above 300 MPa, the time of compression had no effect.     

Thermal stability of polyaniline

Thermal stability data for neutral (emeraldine base) and doped polyaniline with various counter anions are reported. The emeraldine base is a highly heat-stable polymer, with thermal stability up to 420 °C. The thermal stability of doped polyaniline is dependent on the counter anion. The methane sulfonic acid doped polyaniline is stable up to 250 °C. The decomposition of the doped polyaniline is seen as a two-step process. The first step is the loss of the dopant and the second step corresponds to the decomposition of the backbone.     

Electrochemical degradation of polyaniline

The electrochemical degradation of polyaniline was investigated by voltammetry and spectroscopy. The degradation was noticed by a change in the cyclic voltammogram, associated with a decrease in capacity. It occurred at potentials higher than about 0.6 V (versus SCE) in an aqueous solvent and about 0.7 V (versus Ag/Ag⁺) in organic solvents. No degradation was observed below these potentials. The rate of degradation was strongly dependent on the applied potential and on the kind of solvent used. Spectroscopic studies showed that no major chemical modification arose from the degradation.