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.     

Preparation and enhanced stability of flexible supercapacitor prepared from Nafion/polyaniline nanofiber

Polyaniline nanofibers were used to produce a flexible supercapacitor electrode with a specific capacitance of 235 F g^?1. Cycle life and energy density were enhanced after encapsulating the polyaniline nanofiber electrode in Nafion. A specific capacitance of 195 F g^?1 was obtained over 10,000 charge–discharge cycles.A fully flexible, stand alone capacitor comprising two polyaniline nanofiber based electrodes and a PVDF separator was constructed. An initial specific capacitance of 125 F g^?1 (100 mV s^?1) was obtained. This decreased to 95 F g^?1 over 10,000 cycles.     

The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of ferrocenesulfonic acid

The catalytic oxidation of ascorbic acid on the two kinds of polyaniline electrodes (PAn and PAnFc films) has been carried out by cyclic voltammetry, constant potential and constant current methods. PAnFc and PAn films were synthesized in the presence and absence of ferrocenesulfonic acid, respectively. For the electrolysis of ascorbic acid at pH 5.64, the anodic peak potential of ascorbic acid shifts from 0.32 V (vs. SCE) on the bare platinum electrode to 0.05 V on both PAn and PAnFc electrodes. The oxidation current of ascorbic acid on the PAnFc electrode is 31 times as high as on the bare platinum electrode at the electrolysis of the constant potential. The exchange current density is 1.3 mA cm⁻² on the PAnFc electrode and 1.0 mA cm⁻² on the PAn electrode. The catalytic effect is caused by polyaniline itself. Ferrocenesulfonic acid doped in polyaniline plays an important role in enhancing the catalytic activity of polyaniline in the solution of pH >5.     

A highly sensitive non-enzymatic ascorbate sensor based on copper nanoparticles bound to multi walled carbon nanotubes and polyaniline composite

A novel, stable and highly sensitive non-enzymatic ascorbic acid sensor was developed using copper nanoparticles (CuNPs), carboxylated multi-walled carbon nanotubes (MWCNTs) and polyaniline (PANI) composite electrodeposited on gold electrode. The modified Au electrode was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry and impedance spectroscopy. The linear sweep voltammetry peak current showed a linear dependence on the ascorbic acid concentration and a linear calibration curve was obtained in the range, 5–600 μM of ascorbic acid with a correlation coefficient (r) of 0.998. The sensors response time was less than 2 s and detection limit was 1.0 μM (at signal/noise = 3). When tested with serum, fruits and vegetables, the sensor exhibited high electrocatalytic activity, fast response and good selectivity against common interfering species, suggesting its potential to be developed as a non-enzymatic ascorbic acid sensor.     

Voltammetric determination of citric acid and quinine hydrochloride using polypyrrole–pentacyanonitrosylferrate/platinum electrode

Cyclic voltammetry was used to investigate the electrochemical behavior of citric acid (CA) and quinine hydrochloride (QH) at a polypyrrole-pentacyanoferrate/Platinum (PPY–PCNFe/Pt) electrode in aqueous medium. The analytical plots obtained were found to be linear in the concentration range between 1.0 and 9.0 mM for both the analyte solutions. The detection limits (3δ) were found to be 1.17 × 10^?4 M and 1.08 × 10^?5 M for CA and QH analyte solutions, respectively. It was further observed that the diffusion of ionic species into and out of the polymeric film made the PPY–PCNFe/Pt electrode highly electroactive thereby enabling it to efficiently detect the analyte solutions having concentration as low as 1 mM.     

Kinetic study of the electrochemical degradation of polyaniline

The kinetics of the electrochemical degradation of polyaniline (PANI) layers, deposited by electropolymerization and chemical polymerization onto platinum electrode, was investigated in an acid aqueous solution. The degradation rate was shown to depend greatly on the electrode potential applied. First-order rate constants of degradation, obtained from the kinetic data, were shown to vary between 2.87×10⁻⁵ and 3.11×10⁻³ s⁻¹ for thick PANI films, having the electrochemical charge density of 14 mC/cm², and between 2.0×10⁻⁵ and 3.60×10⁻³ s⁻¹ for thin PANI films, having the charge density of 1.5 mC/cm², within the electrode potential range of 0.3–0.9 V versus Ag/AgCl. Two linear regions were found to present on the dependencies of logarithm of the first-order degradation rate constant on electrode potential, one of them having a slope of 0.44 and 1.34 V⁻¹ within electrode potential limits of 0.3–0.6 V, and another one having a slope of 6.37 and 6.39 V⁻¹ within potential limits of 0.6–0.9 V, for thick and thin polymer films, respectively. The results obtained show that the electrochemical degradation of PANI films proceed at a remarkable rate even at low electrode potential values.     

Electronic conduction mechanism in chitin–polyaniline blend

The electrical conductivity of chitin–polyaniline blend doped with HCl has been studied in the temperature range 323–373 K for various blend compositions. Conductivity of blends increases from less than ≈10^?7 S/cm to 2.15 × 10^?5 S/cm, depending on the percentage of polyaniline in the blend due to self-doping of LiCl. When these blends are doped with HCl conductivity raises to ≈9.68 × 10^?2 S/cm. Current–voltage data is analyzed using various models available. The results suggest Schottky–Richardson and one-dimensional variable range hopping mechanisms for undoped blend and one-dimensional variable range hopping mechanism in the case of doped blend.     

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.     

Novel properties of polyaniline nanofibers coated with polycatechol

Polyaniline nanofibers coated with polycatechol, FcPAn/polycatechol, have been prepared with two steps by using repeated potential cycling. First, aniline in a solution containing ferrocenesulfonic acid (Fc) was polymerized on a platinum electrode to form polyaniline nanofibers (FcPAn); second, catechol was polymerized on the polyaniline nanofibers to form FcPAn/polycatechol. The scanning electron microscopy (SEM) images show that the diameters of FcPAn and FcPAn/polycatechol fibers are in the range of 40–60 and 70–90 nm, respectively. The IR and XPS spectra of FcPAn/polycatechol indicate that OH groups and ferrocenesulfonic acid are contained in FcPAn/polycatechol. FcPAn/polycatechol has a good electrochemical activity in the wide pH range. The cyclic voltammogram identifies that FcPAn/polycatechol in the Na₂SO₄ solution with pH 11.0 still has the electrochemical activity at the scan rate of 60 mV s⁻¹. The conductivity of FcPAn/polycatechol is 0.48 S cm⁻¹, which is slightly affected by water. FcPAn/polycatechol nanofibers with the diameter of 70–90 nm have a higher catalytic activity to the electrochemical oxidation of ascorbic acid, compared with FcPAn/polycatechol fibers with the diameter of 140–210 nm.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

Solid-state oxidation of aniline hydrochloride with various oxidants

Aniline hydrochloride was oxidized in the solid state with three different oxidants: ammonium peroxydisulfate, iron(III) chloride, and silver nitrate. Polyaniline salt was obtained after a few hours when ammonium peroxydisulfate was used as an oxidant. The polymerization of aniline hydrochloride with silver nitrate leads to polyaniline only after several days; in the case of iron(III) chloride, aniline oligomers were obtained. The conductivity of the polyaniline was 0.21 S cm^?1 when ammonium peroxydisulfate was applied; it is comparable with the conductivity of a ‘standard’ polyaniline. The oxidation with silver nitrate yields a composite material, polyaniline salt and silver particles, with conductivity 1.5 × 10^?3 S cm^?1. Photoacoustic spectroscopy was employed to study the kinetics of the oxidation reaction. Infrared and UV–vis spectra were efficient tools to characterize the final products, and to compare their molecular structure with that of the polyaniline prepared under ‘standard’ conditions in aqueous medium.     

Morphology and electrical properties of hybrid and sulphonated oxalic acid-doped polyaniline

Polyaniline–polyethylene glycol2000 (PAni–PEG2000) hybrid and sulphonated polyaniline (SPAni) were prepared using oxalic acid as dopant and potassium permanganate as oxidant. The properties of these two conductive polymers were studied in comparison with pure polyaniline (PAni) prepared using the same conditions. The investigated polymers were characterized using FTIR, UV–vis, TGA, TEM, SEM, XRD and their electrical conductivities were also investigated. The morphology of pure polymer was found to be flat ribbon-like form, while presence of polyethylene glycol led to the formation of separate nanospheres. The three polymer samples have different degrees of crystallinity, the highest degree is for SPAni. Unexpectedly, electrical conductivity is in the order SPAni > PAni–PEG2000 > PAni, aging of PAni increases gradually the conductivity of the polymer from 0.0056 to 0.023 S cm^?1 and the increase of temperature gradually decreases the conductivity.     

Facile one-step route to polyaniline–silver nanocomposite particles and their application as a colored particulate emulsifier

Polyaniline–silver nanocomposites were synthesized in the form of colloidal particles by the facile one-step aqueous chemical oxidative dispersion polymerization of aniline using silver nitrate as an oxidant and poly(vinyl alcohol) as a colloidal stabilizer. Aniline monomer was oxidized by silver ions, yielding polyaniline and elemental Ag simultaneously. The synthesized nanocomposite particles were colloidally stable over 2 years and transmission electron microscopy studies indicated the production of spherical, plate and rod-shaped polyaniline–silver nanocomposite particles with a silver core–polyaniline shell morphology. The conductivity of a pressed pellet of the nanocomposite particles using the conventional four-point probe technique was 1.4 × 10^?2 S/cm at 25 °C. The nanocomposite particles behaved as a ‘colored’ particulate emulsifier for the stabilization of transparent oil-in-water emulsions.     

Preparation of polyaniline–TiO2 composite and its comparative corrosion protection performance with polyaniline

Due to strict environmental regulations on the usage of chromate in the coating industries, search for effective inhibitive pigment in replacing those chromate pigments has become necessary. In recent years it has been shown that electrically conducting polymers such as polyaniline (PANI) incorporated coatings are able to protect steel due to their passivating ability similar to that of chromates. This work presents the comparative corrosion protection performance of the coatings containing polyaniline and polyaniline–TiO₂ composite (PTC) on steel in acrylic binder. The PANI and PTC were prepared by chemical oxidative method of aniline by ammonium persulfate. The polymers were characterized by FTIR, XRD and SEM. The corrosion protection performance of the coatings containing PANI and PTC on steel was evaluated by immersion test in 3% NaCl for 60 days and salt fog test for 35 days. The performance of the coatings in both the tests was investigated by open circuit potential measurements and EIS technique. It has been found that the open circuit potential values of PTC containing coating are more nobler by 50–200 mV in comparison to that of coatings with PANI. Besides, the resistance values of the coating containing PTC were more than 10⁷ Ω cm² in the 3% NaCl immersion test after 60 days and 10⁹ Ω cm² in the salt fog test of 35 days which were two orders high in comparison to that of PANI containing coatings. The better performance of PTC containing coatings may be due to uniform distribution of polyaniline which can form uniform passive film on the iron surface.     

Synthesis of sulfonated polyaniline by polymerization of the aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid

The aniline heterodimer 4-aminodiphenylamine-2-sulfonic acid has been polymerized in aqueous ammonium persulfate solution to yield a new form of sulfonated polyaniline (SPAn). This polymer, obtained as a green powder, is soluble in aqueous base (violet solution) and polar solvents (green solution, turning blue on standing). Its FTIR, UV–VIS and EPR spectra are quite similar to those of SPAn obtained by direct ring-sulfonation of polyaniline. The room temperature dc conductivity of the polymer is about 1.3×10⁻⁵ S/cm, indicative of considerable disorder in the sample. Cyclic voltammetry in 1.0 M HCl shows two redox peaks at E_1/2,1=0.50 V and E_1/2,2=0.68 V against Ag/AgCl electrode, characteristic of SPAn.     

In-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors

Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI) composite films were prepared by in-situ electrochemical polymerization of an aniline solution containing different MWCNT contents. The supercapacitive behaviors of these films were investigated with cyclic voltammetry (CV), charge–discharge tests, and ac impedance spectroscopy. The results revealed that the MWCNT/PANI films show much higher specific capacitance (SC), better power characteristic, better cyclic stability, and more promising for applications in supercapacitors than a pure PANI film electrode. The highest specific capacitance value of 500 F g^?1 was obtained for the MWCNT/PANI composite film containing MWCNT of 0.8 wt.%. The improvement mechanisms of the capacitance of the composites are also discussed in detail.     

A novel approach to classify serum glycoproteins from patients infected by dengue using electrochemical impedance spectroscopy analysis

Electrochemical biosensor for serum glycoproteins (SG) from patients infected by dengue fever (DF) based on gold nanoparticles (AuNp) and polyvinyl butyral (PVB) adsorbed on gold electrodes has been investigated. Electrochemical impedance spectroscopy (EIS), in the frequency range from 100 mHz to 100 kHz, was performed on these electrodes, in phosphate buffer (PBS) solution containing 10 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] (1:1) as a redox probe. The electrodes modified with AuNp–Con A–PVB–BSA–SG showed larger electron transfer resistances than those modified with AuNp–Con A–PVB–BSA. The impedance spectra showed an increase in the charge transfer resistance when Con A interacted with SG. Moreover, the charge transfer resistance obtained with DF was larger than that obtained with negative serum. The resulting biosensor is capable to recognize SG from patients infected by DF.     

Conducting polymer embedded with nanoferrite and titanium dioxide nanoparticles for microwave absorption

The present paper deals with the synthesis of conducting ferrimagnetic polyaniline nanocomposite embedded with γ-Fe₂O₃ (9–12 nm) and titanium dioxide (70–90 nm) nanoparticles via a micro-emulsion polymerization. The microwave absorption properties of nanocomposite in 12.4–18 GHz (Ku-band) frequency range shows shielding effectiveness due to absorption (SE_A) value of ?45 dB, which is much higher than polyaniline composite with iron oxide and polyaniline–TiO₂ composites. The higher EMI shielding is mainly arising due to combined effect of γ-Fe₂O₃ and TiO₂ that leads to more dielectric and magnetic losses which consequently contributed to higher values of shielding effectiveness. XRD analysis of the nanocomposite reveals the incorporation of nanoparticles in the conducting polymer matrix while the thermal gravimetric analysis (TGA) demonstrates that the nanocomposite is stable up to 250 °C.     

Optical evidence of electrochemical modification of polyaniline induced by tetra-fluoro-hydroquinone

We have made an attempt to study electrochemically induced modification of ITO/PANI electrode in tetra-fluoro-hydroquinone (4F-hydroquinone) solution. The conditions at which the host molecule (of 4F-hydroquinone) incorporates into polyaniline were investigated, and the modifications in PANI electrode were monitored by optical absorption spectra measurements.PANI films were exposed to three different modifying conditions: a long-cycle polarization in acid solutions (pH range 0.4–3.2, potential limits between −0.35 and 0.8 V versus SCE) without and with 4F-hydroquinone added and a chemical interaction between PANI and 4F-quinone solution for different times at pH 6. We found that modification is a pH-dependent process and can only occur at pH above 3. Cyclic treatment in electrolyte containing 4F-hydroquinone at pH 3.2 leads to 4F-hydroquinone residue incorporation into the polymer backbone that can be viewed as a new optical absorption band of the polymer (550–600 nm). Other optical transitions of PANI are also changed due to modification. A π–π¹ transition (320–350 nm) is broader and seems to contain two components. A localized polaron absorption (435–450 nm) is several folds more intensive in modified PANI. A conduction band absorption (800–820 nm) shows a blue shift and this band still appears at potentials where the loss of conductivity has occurred for non-modified polymer. We have proposed that modification emerged from interaction of the acid polymer centers and 4F-hydroquinone molecules oxidized during cycling.     

Electrochemical synthesis and corrosion behavior of polyaniline-benzoate coating on copper

Electrochemical polymerization of polyaniline (PANI) coating on copper electrode was performed galvanostatically in the current density range between 0.50 and 1.25 mA cm^?2, from aqueous solution of 0.3 mol dm^?3 sodium benzoate and 0.2 mol dm^?3 aniline. The corrosion behavior of PANI coated copper and copper electrode exposed to 0.5 mol dm^?3 sodium chloride solution was investigated by potentiodynamic and electrochemical impedance spectroscopy techniques. It was observed that thin PANI (5 μm) coating had provided efficient protection (～96%) to copper in 0.5 mol dm^?3 sodium chloride solution. Unusual initial impedance behavior to that normally observed with conventional organic coatings was attributed to dedoping of benzoate anions from the polymer coating.