Improving the electrochemical performance of polyaniline electrode for supercapacitor by chemical oxidative copolymerization with p-phenylenediamine

A series of poly(aniline-co-p-phenylenediamine) (P(ANI-co-PPDA)) copolymers were synthesized via the chemical oxidative polymerization of aniline with p-phenylenediamine (PPDA) as the comonomer. The structure and morphology of the P(ANI-co-PPDA) copolymers prepared with different feeding ratio of PPDA under different polymerizing temperature were compared with the two homopolymers polyaniline (PANI) and poly(p-phenylenediamine) (PPPDA). It is interesting to find that the electrical conductivity, specific capacitance and cycling stability of the P(ANI-co-PPDA) copolymer electrode materials were obviously improved with certain feeding ratio of PPDA, compared with those two homopolymers.     

Electropolymerization of polyaniline on titanium oxide nanotubes for supercapacitor application

Vertically aligned polyaniline (PANI) nanotubes have great potential application in supercapacitor electrode material. In this paper we have investigated facile growth of PANI nanotubes on a titanium nanotube template (TNT) using electrochemical polymerization. The morphology of PANI nanostructures grown over TNT is strongly influenced by the scan rate in the electrochemical polymerization. The growth morphology of PANI nanotubes has been carefully analyzed by field emission scanning electron microscopy. The detailed growth mechanism of PANI nanotubes has been put forward. Specific capacitance value of 740 F g⁻¹ was obtained for PANI nanotube structures (measured at charge–discharge rate of 3 A g⁻¹).     

A novel electrochemical DNA biosensor based on graphene and polyaniline nanowires

A novel DNA biosensor based on oxidized graphene and polyaniline nanowires (PANIws) modified glassy carbon electrode was developed. The resulting graphene/PANIw layers exhibited good DPV current response for the complementary DNA sequences. The good electron transfer activity might be attributed to the effect of graphene and PANIw. Graphene and PANIw nanolayers film with highly conductive and biocompatible nanostructure were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immobilization of the probe DNA on the surface of electrode was largely improved due to the unique synergetic effect of graphene and PANIw. Under optimum conditions, the biosensor exhibited a fast amperometric response, high sensitivity and good storage stability for monitoring DNA. The current response of the sensor increases linearly with the concentration of target from 2.12 × 10⁻⁶ to 2.12 × 10⁻¹² mol l⁻¹ with a relative coefficient of 0.9938. The detection limit (3σ) is 3.25 × 10⁻¹³ mol l⁻¹. The results indicate that this modified electrode has potential application in sensitive and selective DNA detection.     

Preparation of polyaniline nanowire arrayed electrodes for electrochemical supercapacitors

Polyaniline (PANI) nanowire arrayed electrodes were successfully synthesized by means of anodic deposition technique using the membrane-template synthesis route. The desired three-dimensional architecture of PANI nanowire arrayed electrodes was characterized with field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) techniques. It was found that the co-deposition nanowires were regular size and continuous with an average diameter of about 30 nm, and the nanowires have an amorphous nature. The electrochemical characterization was performed in 2 M H₂SO₄ aqueous solution. The capacitance of the PANI nanowire arrayed electrode at a charge–discharge current density of 5 Ag⁻¹ is 1142 Fg⁻¹. The nanowire arrayed electrodes showed an excellent capacitive ability for the facility of electrolyte penetration, the ease of proton exchange/diffusion and the metallic conductivity of PANI nanowire arrayed electrodes.     

Chemical and electrochemical synthesis of polyaniline/platinum composites

The synthesis of polyaniline/platinum composites (PANI/Pt) has been achieved using both chemical and electrochemical methods. The direct chemical synthesis of PANI/Pt proceeds through the oxidation of aniline by PtCl₆²⁻ in the absence of a secondary oxidant. SEM images of these samples indicate that the Pt particles are on the order of ∼1 μm for the chemically prepared composite. Electrochemical PANI/Pt synthesis is initiated by the uptake and reduction of PtCl₆²⁻ into an a priori electrochemically deposited PANI film. This method produces a uniform dispersion of Pt particles with smaller particles with diameters ranging between 200 nm and 1 μm. The results indicate that electrochemical methods may be more suitable for controlling particle dimension. Both materials show reduced proton doping relative to PANI without Pt, indicating the metal particles directly influence proton doping and the oxidation state of the polymer. The electrochemical data indicate that the conductivity in solution is sufficient such that the normal acid doping is attainable for PANI/Pt produced using either synthetic method.     

Electrochemical properties of an interface between titanium and fibroblasts L929

Various electrochemical measurements were performed on titanium with and without culturing murine fibroblasts L929 to characterize the effects of cells on interface electrochemical properties between titanium and cells. Open-circuit potential of titanium decreased with L929 cells, which was caused by the shift of equilibrium potential between cathodic and anodic reactions indicated by the decrease in cathodic current density with L929 cells. In cathodic potential step test, the decrease in current density following to the peak current density was delayed with L929 cells, indicating that diffusivity of molecules and ions decreased with the cells. In addition, alternating current impedance measurement and data approximation to the electrical equivalent circuit model revealed that the circuit element for diffusion resistance of biomolecule adsorption layer increased with L929 cells. Consequently, the effect of cells on the interface property is the retardation of diffusion through the biomolecule adsorption layer due to the increase in biomolecule density with extracellular matrix consisting with proteins and glycosaminoglycans generated by the cells.     

Fabrication and electrochemical characterization of polyaniline nanorods modified with sulfonated carbon nanotubes for supercapacitor applications

The novel composites of sulfonated multi-walled carbon nanotubes (sMWCNTs) modified polyaniline (PANI) nanorods (PANI/sMWCNTs) were synthesized successfully by in situ oxidative polymerization method in the HClO₄ solution. FTIR and Raman spectra revealed the presence of π–π interaction between the PANI and the sulfonated carbon nanotubes and the formation of charge transfer composites. It was found that the specific capacitance of the PANI/sMWCNT composites was markedly influenced by their morphological structure and the content of PANI which was coated onto the sMWCNT. The specific capacitance of the PANI/sMWCNT composite exhibited a maximum value of 515.2 F g⁻¹ at the 76.4 wt% PANI. The charge–discharge tests showed the PANI/sMWCNT composites possessed a good cycling stability (below 10% capacity loss after 1000 cycles) compared to PANI nanorods.     

Identification of inductive behavior for polyaniline via electrochemical impedance spectroscopy

Polyaniline (PANI) film electrodeposited in HCl medium using cyclic voltammetry (CV) with an upper potential limit of 0.90 V, exhibited an inductive behavior. PANI films deposited with different conditions were subjected to various applied potentials and the impedance characteristics were recorded through electrochemical impedance spectroscopy (EIS). The impedance results clearly reveal the existence of inductive behavior to PANI. Inductive behavior was observed for PANI films deposited with conditions which favor benzoquinone/hydroquinone (BQ/HQ) formation and further evidenced by X-ray photoelectron spectroscopy (XPS). A comparative analysis of the EIS and XPS results of PANI films prepared under similar conditions with the upper potential limits of 0.75 and 0.90 V, respectively, clearly documented that the presence of BQ/HQ, the degradation product of PANI, formed during the electrochemical polymerization at the upper potential limits causes inductive behavior to PANI.     

One-dimensional growth and electrochemical properties of polyaniline deposited by a pulse potentiostatic method

One-dimensional growth of polyaniline (PANI) was conducted on carbon cloth through a pulse potentiostatic method. Hydrolysis of PANI was depressed, and the generated PANI film (PPM) displayed improved electroactivities. The specific capacitance of PPM was increased by 39% when compared to that of PANI film made by the conventional potentiostatic method (PM). The influences of the upper limit potential of the pulse potentiometry and the acidity of the polymerization solution on surface morphologies, electroactivities and conformation of the PANI films were studied by SEM, cyclic voltammetry, chronopotentiometry and UV-Vis spectrometry.     

Electrochemical synthesis and characterization of polyaniline thin film and polyaniline powder

The polyaniline thin film electrode and powder have been synthesized on graphite electrodes from 0.5 M hydrochloric acid solution under galvanostatic conditions. The water insoluble and acetone soluble polyaniline mass fractions of the powder, as well as the polymerization efficiency, based on the emeraldine salt have been determined. The morphology of the obtained emeraldine salt powder has been investigated by the optical microscopy.     

Preparation, electrochemical characterization and charge–discharge of reticulated vitreous carbon/polyaniline composite electrodes

Polyaniline was electrodeposited onto reticulated vitreous carbon – RVC – in order to obtain a tridimensional composite electrode. Three variations of these electrodes were analysed: a small-anion-doped polyaniline (RVC/Pani), a polyanion-doped polyaniline (RVC/PaniPSS) and a bi-layer type formed by an inner layer of the first electrode and an outer layer of the second one (RVC/Pani/PaniPSS). These composites were characterized by cyclic voltammetry, scanning electronic microscopy and electrochemical impedance spectroscopy. Photomicrographies, voltammetric profiles and impedance data pointed to different morphological and electrochemical characteristics for polyaniline doped with small or large anions, and a mixed behavior for the bi-layer electrodes. Charge–discharge tests for these tridimensional (3D) electrodes, employed as the cathode in lithium batteries, indicated better performance for the RVC/Pani electrode. These RVC composites presented higher specific capacities when compared with those obtained for Pani deposited onto bidimensional substrates.     

On the electrochemical and spectroscopic properties of a soluble polyaniline parent copolymer

Copolymers of aniline and 2-ethylaniline can be easily formed by electrochemical or chemical oxidation in acidic medium, but the composition of the polymeric chain differs from the composition of the synthesis solution. Copolymers formed from precursor solutions containing less than 30% (in moles) of 2-ethylaniline show intermediate properties between those of the homopolymers, and these properties vary gradually with the amount of 2-ethylaniline units in the copolymeric chain. The properties of those copolymers have been studied by UV-Vis and resonance Raman spectroscopies, cyclic voltammetry, two-probe conductivity and solubility measurements. Results obtained by these techniques corroborate the formation of a block copolymeric material.     

Determination of the kinetic pathway in the electrochemical reduction of titanium dioxide in molten calcium chloride

An investigation into the kinetics of the electrochemical reduction of titanium dioxide (TiO₂) to titanium metal (Ti) in molten calcium chloride has been performed. Partially reduced samples were prepared by terminating the reduction process after different reaction times and characterised by means of X-ray diffraction analysis. Based on the time-dependent changes of phase composition as well as thermodynamic and kinetic considerations, the reaction path has been derived. The key result is that the reduction proceeds through a number of individual stages some of which involve the formation and decomposition of calcium titanates. Several of the partially reduced samples were examined further through scanning electron microscopy and energy-dispersive X-ray analysis. The results demonstrate that the electrochemical reduction of titanium dioxide to titanium metal is accompanied by substantial changes in the microstructure.     

Effect of secondary dopants on electrochemical and spectroelectrochemical properties of polyaniline

Polyaniline (PANI) was doped with poly(styrene sulfonic acid) (PSS) via doping-dedoping-redoping procedure. Incorporation of PSS in PANI resulted modifications in electrochemical and electrochromic properties, morphology and polymer structure of the polymer film as evidenced by the results of cyclic voltammetry, in situ UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis and conductivity measurements. PANI doped with PSS was found to have a cross-link/branched structure with a minimum degradation product. The absence of degradation products improves the electrochemical, electrochromic properties and thermal stability of the PANI layer for electrochromic applications.     

High capacitance properties of polyaniline by electrochemical deposition on a porous carbon substrate

Electrochemical deposition of polyaniline (PANI) is carried out on a porous carbon substrate for supercapacitor studies. The effect of substrate is studied by comparing the results obtained using platinum, stainless steel and porous carbon substrates. PANI deposited at 100 mV s⁻¹ sweep rate by potentiodynamic technique on porous carbon substrate is found to possess superior capacitance properties. Experimental variables, namely, concentrations of aniline monomer and H₂SO₄ supporting electrolyte are varied and arrived at the optimum concentrations to obtain a maximum capacitance of PANI. Low concentrations of both aniline and H₂SO₄, which produce PANI at low rates, are desirable. The PANI deposits prepared under these conditions possess network morphology of nanofibrils. Capacitance values as high as 1600 F g⁻¹ are obtained and PANI coated carbon electrodes facilitate charge-discharge current densities as high as 45 mA cm⁻² (19.8 A g⁻¹). Electrodes are found to be fairly stable over a long cycle-life, although there is some capacitance loss during the initial stages of cycling.     

The electrochemical deposition of polyaniline at pure aluminium: electrochemical activity and corrosion protection properties

Polyaniline films were electrodeposited at pure aluminium from a tosylic acid solution containing aniline. These polymer films exhibited similar characteristics as pure polyaniline electrosynthesized at an inert platinum electrode, when removed from their respective substrates and dissolved in NMP. Both polymers had similar molecular weights and similar UV-visible absorption spectra. However, the aluminium substrate had a considerable effect on the electrochemical activity of the films. The polyaniline films deposited at aluminium appeared to lose electroactivity and the electrochemical impedance data were governed by the oxidized aluminium substrate. This is consistent with a galvanic interaction between the polymer and the aluminium substrate, giving rise to oxidation of the aluminium and reduction of the polymer. The polyaniline deposits appeared to offer only a slight increase in the corrosion resistance of aluminium. Surface potential measurements, using a scanning vibrating probe, showed that attack initiated underneath the polymer under anodic polarization conditions, indicating that chloride anions diffuse across the polymer to react at the underlying aluminium substrate.     

Synthesis and dielectric properties of polyaniline/titanium dioxide nanocomposites

Two series of polyaniline–TiO₂ nanocomposite materials were prepared in base form by in situ polymerization of aniline with inorganic fillers using TiO₂ nanoparticles (P25) and TiO₂ colloids (Hombikat), respectively. The effect of particle sizes and contents of TiO₂ materials on their dielectric properties was evaluated. The as-synthesized polyaniline–TiO₂ nanocomposite materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermal analysis (DTA/TGA), and X-ray diffraction (XRD). Dielectric properties of polyaniline–TiO₂ nanocomposites in the form of films were measured at 1 KHz–1 MHz and a temperature range of 35–150 °C. Higher dielectric constants and dielectric losses of polyaniline–TiO₂ nanocomposites than those of neat PANI were found. PANI–TiO₂ nanocomposites derived from P25 exhibited higher dielectric constants and losses than those from Hombikat TiO₂ colloids. Electrical conductivity measurements indicate that the conductivity of nanocomposites is increased with TiO₂ content. The dielectric properties and conductivities are considered to be enhanced due to the addition of TiO₂, which might induce the formation of a more efficient network for charge transport in the base polyaniline matrix.     

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 via titanium and boron co-doping

Titanium and boron are simultaneously introduced into LiNi_0.8Co_0.1Mn_0.1O₂ to improve the structural stability and electrochemical performance of the material. X-ray diffraction studies reveal that Ti⁴⁺ ion replaces Li⁺ ion and reduces the cation mixing; B³⁺ ion enters the tetrahedron of the transition metal layers and enlarges the distance of the [LiO₆] layers. The co-doped sample has spherical secondary particles with elongated and enlarged primary particles, in which Ti and B elements distribute uniformly. Electrochemical studies reveal the co-doped sample has improved rate performance (183.1 mAh·g^-1 at 1 C and 155.5 mAh·g^-1 at 10 C) and cycle stability (capacity retention of 94.7% after 100 cycles at 1 C). EIS and CV disclose that Ti and B co-doping reduces charge transfer impedance and suppresses phase change of LiNi_0.8Co_0.1Mn_0.1O_2.     

Corrosion protection of steel by polyaniline blended coating

Phosphate doped polyaniline was synthesized from aqueous phosphoric acid containing aniline by chemical oxidation method using ammonium persulphate as oxidant. The polymer was characterized by UV–vis and FT-IR spectroscopic techniques. Using this polymer, a paint with 1% polyaniline was prepared with epoxy binder. The corrosion resistant property of the polymer containing coating on steel was found out by open circuit potential measurements and electrochemical impedance spectroscopic method in 0.1 N HCl, 0.1 N H₃PO₄ and 3% NaCl for a duration of 50 days. The coating was able to protect the steel more in 0.1 N H₃PO₄ and 3% NaCl media than in 0.1 N HCl.     

Electrochemical modification of cation exchange membrane with polyaniline for improvement in permselectivity

A novel method of modification of cation exchange membrane for improved permselectivity is reported in this paper. Acrylic acid grafted fluorinated ethylene propylene copolymer membrane after sulphonation (FEP-g-AA-SO₃H) was used as the cation exchange membrane for modification. Polyaniline is deposited electrochemically on to the membrane. The deposition of polyaniline starts from the surface of the membrane and growth proceeds inside the membrane. The amount of polyaniline deposited depends upon the polymerization time. The presence of polyaniline is confirmed by FTIR, scanning electron microscopy, X-ray mapping, cyclic voltammetry and ion exchange capacity measurements. The electrodialysis experiments show improved permselectivity for divalent cations.