Preparation of porous nanorod polyaniline film and its high electrochemical capacitance performance

Nano-sized polyaniline (PANI) films were electrochemically deposited onto an ITO substrate by a pulse galvanostatic method (PGM) in an aqueous solution. The morphology of the as-prepared PANI film was characterized using a field emission scanning electron microscope (FESEM). It was observed that the as-prepared PANI films were highly porous, and showed a nano-sized rod-like or coralline-like morphology depending on the charge loading performed in the electropolymerization process. Furthermore, the PANI films were electrochemically measured by the galvanostatic charge–discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests in 1 mol L^?1 HClO₄ solution. The results showed that such PANI films had a favorable electrochemical activity and an excellent capacitance. The rod-like PANI film prepared with the charge loading of 1000 mC showed the highest discharge capacitance of 569.1 F g^?1 at a low current density of 1 A g^?1. The discharge capacitance retained 97.7% after 1000 cycles at a large current density of 10 A g^?1.     

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.     

Large-area network of polyaniline nanowires supported platinum nanocatalysts for methanol oxidation

Nanocomposites comprised of Pt nanoparticles and electrically conducting polymers were prepared and tested for the electrocatalytic performance towards oxidation of methanol. Films of polyaniline (PANI) synthesized independently by potentiostatic and galvanostatic method, PANI(V) and PANI(I), respectively, were used as the supporting matrix for loading Pt nanoparticles. PANI(V), PANI(I), PANI(V)/Pt, and PANI(I)/Pt films were characterized for structure and morphology using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM image of PANI(I) reveals that the particles are highly porous and interconnected nanowires, whilst PANI(V) particles are granular. The large surface area in the nanofibrillar PANI(I) makes the dispersion of Pt particle with a lesser time for the deposition of Pt particles. The porous network structure of PANI(I) helps in effective dispersion of Pt particles (about 10–20 nm) and facilitates easy access of methanol to the catalytic sites. The electrocatalytic activity of PANI(I)/Pt is much higher (current density (24.7 mA/cm² mg) at 0.68 V) in comparison to PANI(V)/Pt and bulk Pt electrodes (the current density values of 5.5 and 7.5 mA/cm² mg).     

Synthesis and characterization of water-soluble polyaniline films

Water-soluble polyaniline (PANI) films were synthesized by using poly(2-acrylamido-2-methyl propanesulphonic acid) (PAMPS) as a water-soluble dopant. The aqueous solution conductivities of PANI/PAMPS films were in the range of 10^?1 to 10⁰ mS/cm which were increased compared with PAMPS films aqueous solution. The structure and microstructure characteristics of PANI/PAMPS films which varied greatly with different molar ratios of aniline/AMPS were investigated by SEM, UV–vis absorption spectroscopy and XRD analysis. Moreover, the photoluminescence properties of PANI/PAMPS films were studied, and water-soluble PANI having appropriate size fitted to the increase of fluorescence emission intensity. PANI/PAMPS films were also investigated by FTIR spectroscopy and TG analysis.     

The manufacture and properties of polyaniline nano-films prepared through vapor-phase polymerization

We succeeded in the chemical preparation of nano-level thick polyaniline (PANI) emeraldine salt films on plastic substrate by an in situ vapor-phase deposition (VDP) polymerization method under ambient conditions, using a self-assembly method which is unprecedented. Homogeneous conductive PANI thin films were uniformly fabricated at nano-level thickness (20–100 nm), but their morphologies could grow as polycrystalline grains of a highly ordered structure, depending on the deposition conditions. The grain size was also controlled between 30 and 100 μm depending on the deposition time/temperature. The surface resistance of PANI films was enhanced up to 10⁴ Ω/square with crystallization and light transmittance was increased up to 90% in the case of a film less than 30 nm thick. A typical spectrum for the oxidized PANI, the emeraldine salts form, showing π–π^* transition and a polaron lattice were observed by UV–visible/IR and infrared /Raman spectroscopy.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

Synthesis and characterization of polyaniline–ZnO composite and its dielectric behavior

Films of polyaniline (PANI) and PANI–zinc oxide (ZnO) composites have been synthesized by solution cast and spin coating technique. The ZnO powder of particle size 100–200 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infra red (FTIR) and the results were compared with polyaniline films. Dielectric properties of PANI and PANI–ZnO composite films have been investigated between frequency ranges of 8.5 and 13.0 GHz. The ‘a’ lattice parameter of ZnO was found to increase and the ‘c’ lattice parameter was found to decrease after ZnO–PANI composite formed. The characteristic FTIR peaks of PANI were found to shift to higher wave number in ZnO–PANI composite. These observed effects have been attributed to interaction of ZnO particles with PANI molecular chains. Dielectric constant of PANI–ZnO composite film was found to be smaller than the PANI film. The decrease of dielectric constant in PANI–ZnO films as compared to PANI was attributed to the interfaces formed between ZnO particles and PANI.     

Transmembrane redox reactions through polyaniline membrane doped with fullerene C60

Polyaniline (PANI)-C₆₀ membranes were chemically synthesized with fullerene C₆₀ content of 0.2, 0.5, 1, 2 and 3 mol% (relative to aniline fragment) respectively, and then systematically characterized with FTIR, field emission scanning electron microscopy (FESEM), XPS and electrochemical impedance spectroscopy (EIS). It is demonstrated that electron/ion coupled transport across PANI-C₆₀ membrane is possible in the presence of oxidizing agent at one side of the membrane and reducing agent at the other side. If 0.05 M acidic solution of FeCl₃ was used as the oxidizing agent and 0.3 M ascorbic acid as the reducing agent, a typical value of transmembrane transport rate of redox equivalents was 3.1 × 10⁻⁸ mol s⁻¹ cm⁻² with the membrane containing 0.5% C₆₀. This value was one order higher than that for HCl doped PANI membrane at identical conditions, which can be explained by superimposed C₆₀ doping and acid doping. The 0.5% content of C₆₀ is optimal and at higher content the rates of transmembrane redox transport decrease.     

Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites

Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO₂) nanoparticles of 4.5 nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO₂ nanocomposites, prepared at various initial aniline/TiO₂ mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO₂ nanocomposites increases in the range 3.8 × 10^?4 to 1.1 × 10^?3 S cm^?1 by increasing aniline/TiO₂ mole ratio from 1 to 10. The morphology of PANI/TiO₂ nanocomposites significantly depends on the initial aniline/TiO₂ mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO₂ mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO₂ mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40 nm, an inner diameter 4–7 nm) and nanorods (diameter 50–90 nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70 nm, 160–350 nm, and ～1–3 μm, respectively). The PANI/TiO₂ nanocomposite synthesized at aniline/TiO₂ mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO₂ mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO₂ nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO₂ nanocomposites was observed.     

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.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

Redox behaviour of polyaniline–palladium catalytic system in the presence of formic acid

Redox behaviour of polyaniline (PANI) films containing chemically incorporated palladium particles in the presence of formic acid was studied. Two types of PANI–Pd hybrids were prepared: PANI-PdHA and PANI-PdLA, depending on the acidity of the PdCl₂ solution used for the introduction of palladium into the polymer matrix. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the nature of processes involved upon the decomposition of formic acid on polyaniline–palladium hybrids. In particular, UV–vis changes of both kinds of films were followed in situ (in 1 M aqueous HCOOH solution) as a function of time. Rather unexpectedly, the redox properties of polyaniline films are found to be significantly altered in the presence of palladium particles. Particles of Pd⁰ promote the reduction of PANI from the most oxidized and semi-oxidized states to the most reduced one with simultaneous decomposition of formic acid.     

Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.     

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.     

Photolithographic patterning of conducting polyaniline films via flash welding

In this work, two significant advances in photolithographic patterning of polyaniline (PANI) films are reported. Firstly, flash welding was enhanced through the use of polymeric substrates, enabling complete penetration of the welding of PANI films with thicknesses ranging from 5 to over 14 μm, significantly thicker than reported previously. Masking of parts of the PANI films during flash welding enabled the formation of adjacent conducting and insulating regions as the welding changes the electrical properties of the film. Raman spectroscopy was used to determine the sharpness of these edges, and indicated that the interface between the flash welded and masked regions of the PANI films was typically less than 15 μm wide. Secondly, using longpass filters, light with a wavelength less than 570 nm was found not to contribute to the welding process. This was confirmed by the use of a 635 nm laser diode for welding the PANI films. This novel approach enabled patterning of PANI films using a direct writing technique with a narrow wavelength light source.     

Synthesis of polyaniline/NiO nanobelts by a self-assembly process

Polyaniline (PANI) nanotubes (∼180 nm in diameter) were synthesized in the presence of sodium dodecylbenzenesulfonate (SDBS) as a micellar template and dopant, whereas PANI/NiO nanobelts (300–700 nm in diameter) were obtained with the addition of NiO nanoparticles (∼10 nm in diameter). Results showed that the size of PANI/NiO composite nanobelts increased with an increase content of NiO nanoparticles. XRD, Fourier transform infrared (FTIR) and UV–vis spectroscopy were used to characterize the chemical structures of PANI nanotubes and PANI/NiO nanobelts. The thermal stability and conductivity of samples were affected by the content of NiO. The coordination bonds between NiO and aniline were the key factor that resulted in the morphological change of PANI.     

Synthesis of polyaniline nanostructures via soft template of sucrose octaacetate

Highly crystallized polyaniline (PANI) nanostructures were polymerized by oxidative polymerization in the presence of sucrose octaacetate acting as an in situ seed and a soft template, and ammonium peroxydisulfate (APS) acting as an oxidizing agent. PANI nanofibers and nanorods were obtained using 2 and 3 g sucrose octaacetate, respectively. The nanostructures containing irregular-shaped agglomerates, such as particulate particles and scaffolds were observed with increasing the concentrations of sucrose octaacetate. The polymerized PANI was characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetry analysis (TGA). Results showed that the presence of sucrose octaacetate during polymerization could only induce a change in morphology, but could not influence the molecular structure of the resulting PANI. Compared with those derived with 1, 3, and 4 g sucrose octaacetate, the polymerized PANI from 2 g sucrose octaacetate possessed higher thermal stability and electrical conductivity due to its higher crystallinity and highly ordered structure. A mechanism for the formation of PANI nanostructures is also proposed.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

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.