Synthesis of graphene/vitamin C template-controlled polyaniline nanotubes composite for high performance supercapacitor electrode

A graphene nanosheet/polyaniline nanotube (GPNT) composite is prepared for the first time by in-situ chemical oxidative polymerization of aniline using vitamin C as a structure directing agent. The vitamin C molecules lead to the synthesis of polyaniline (PANI) nanotubes through the development of rod-like assembly by H-bonding in an aqueous medium. The initially synthesized graphene oxide/polyaniline nanotubes composite is reduced to graphene using hydrazine monohydrate followed by re-oxidation and protonation of the PANI to produce the GPNT nanocomposite. This novel composite showed a high specific capacitance of 534.37 F/g and an excellent energy density of 74.27 Wh/kg at a constant current of 0.5 mA. Besides, the GPNT composite exhibited excellent cycle life with 91.4% specific capacitance retained after 500 charge-discharge cycles. The excellent performance is due to the synergistic combination of graphene which provides good electrical conductivity and mechanical stability, and PANI nanofiber which deals with good redox activity.     

Preparation and electrochemical performance of polyaniline-based carbon nanotubes as electrode material for supercapacitor

Nitrogen-containing carbon nanotubes (CNTs) with open end and low specific surface area were prepared via the carbonization of polyaniline (PANI) nanotubes synthesized by a rapidly mixed reaction. On the basis of analyzing the morphologies and structures of the original and carbonized PANI nanotubes, the electrochemical properties of PANI-based CNTs obtained at different temperatures as electrode materials for supercapacitors using 30 wt.% aqueous solution of KOH as electrolyte were investigated by galvanostatic charge/discharge and cyclic voltammetry. It was found that the carbonized PANI nanotubes at 700 °C exhibit high specific capacitance of 163 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent rate capability in KOH solution. Using X-ray photoelectron spectroscopy measurement the nitrogen state and content in PANI-CNTs were analysed, which could play important roles for the enhancement of electrochemical performance. When the appropriate content of nitrogen is present, the presence of pyrrole or pyridone and quaternary nitrogen is beneficial for the improvement of electron mobility and the wettability of electrode.     

Fabrication and characterization of polyaniline coated carbon nanofiber for supercapacitor

Polyaniline coated carbon nanofiber was fabricated using one-step vapor deposition polymerization technique. Fourier transform infrared (FT-IR) spectra and transmission electron microscope (TEM) images indicated that uniform and ultrathin conducting polymer layers were formed on the carbon nanofiber surfaces regardless of the coating thickness. It was also confirmed that the thickness of polyaniline layer could be conveniently tuned by the feeding amount of monomer. The coating thickness was dependent on initiator/monomer ratio, the vacuum pressure of reaction chamber and polymerization temperature. Among them, the vacuum pressure was a major factor to control the coating thickness of polyaniline onto the carbon nanofiber surface. In addition, the electrochemical analysis demonstrated that polyaniline coated carbon nanofiber showed an improved performance as supercapacitor. The specific capacitance of polyaniline coated carbon nanofiber exhibited a maximum value of 264 F/g when the thickness of polyaniline layer was ca. 20 nm.     

Preparation and electrochemical investigation of the polyaniline/activated carbon nanocomposite for supercapacitor applications

The polyaniline (PANI)/activated carbon (AC) nanocomposite electrodes were prepared by electropolymerization of aniline monomers on the surface of AC/polyvinyl alcohol (PVA) electrodes for supercapacitor studies. Fourier transforms infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses were performed to characterize the structure and morphology of the nanocomposite electrodes. The electrochemical properties of the prepared nanocomposite electrodes and the supercapacitive behavior of the PANI, AC, and AC/PANI/PVA electrodes were investigated using cyclic voltammetry (CV) and galvanostatic charge/discharge measurements, respectively. Morphological studies showed that a thin film of PANI has been uniformly deposited on the porous surface of AC electrode, and an ordered arrangement of nanostructures with interlinked porous network has been made. Electrochemical measurements showed that AC particles prevent the degradation of PANI chains during charge/discharge cycles. The specific capacitance of the AC/PANI/PVA nanocomposite electrode was 338.15 F/g which is higher than that of the pristine AC electrode (0.08 F/g). This is due to the contribution of PANI chains by their pseudocapacitance (redox reaction) properties. Although the specific capacitance of PANI electrode (378.57 F/g) was greater than that of the nanocomposite electrode, the cyclic stability of the PANI electrode was lower than that of the AC/PANI/PVA nanocomposite electrode.     

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).     

Synthesis and characterization of hybrid composites based on carbon nanotubes

Multi-wall carbon nanotubes (CNTs) were coated with protonated polyaniline (PAni) in situ during the chemical polymerization of aniline. Uniform coating of CNT with PAni was observed by scanning electronic microscopy. An improvement in the covering of CNT composites was found by the association of poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT). The conductivity of composites has been compared with the conductivity of the PAni and CNT. A maximum conductivity of 96.8 S cm⁻¹ has been found for a PAni/PDMcT/CNT composite. High capacitance value (289.4 F g⁻¹) was also determined for this composite, indicating that all materials, PAni, PDMcT and CNT, remain active during the charge–discharge cycling. The reduction in the capacitance after 100 cycles was found to be less than 25%. The capacitive behavior of all materials was confirmed by impedance analysis.     

Novel electrochemical sensing platform based on palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes nanocomposite for sensitive detection of niclosamide

We reported an one-pot ultrasonic-assisted method for the preparation of palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes (PNRs/SPCNPs-g-CNTs) nanocomposite, which was used to modify the glassy carbon electrode (GCE) for the fabrication of PNRs/SPCNPs-g-CNTs/GCE sensor. For the PNRs/SPCNPs-g-CNTs nanocomposite, PNRs with good stability presented large specific surface area and high adsorption, which promoted the enrichment of NA molecules on the electrode surface. SPCNPs with pearl chain-like nanostructure exhibited good electrical conductivity, and the combination of SPCNPs and g-CNTs with high graphitization degree formed an interconnected carbon conductive network with excellent electrical conductivity, which enhanced the charge transport efficiency. Moreover, the interconnected carbon conductive network of SPCNPs-g-CNTs not only promoted the dispersion degree of PNRs but also made up for the poor conductivity property of PNRs. When used for the detection of niclosamide (NA), an acceptable limit of detection (3.6 nM) was achieved at the PNRs/SPCNPs-g-CNTs/GCE sensor in linear NA concentration range of 0.01–10 μM. The PNRs/SPCNPs-g-CNTs/GCE sensor exhibited good reproducibility, repeatability, and anti-interference performance. For the practicability measurement, the fabricated sensor showed good practicability with satisfactory recoveries (97.0–102.7%) and low RSD values of 0.99–4.78% for the detection of NA in tap water and lake water samples.     

Fabrication of carbon nanotubes/polypyrrole/carbon nanotubes/melamine foam for supercapacitor

The carbon nanotubes (CNTs) have been loaded on the melamine foam (MF) to form the composite (CNTs/MF) by dip‐dry process, then polypyrrole (PPy) is coated on CNTs/MF (PPy/CNTs/MF) through chemical oxidation polymerization by using FeCl₃·6H₂O adsorbed on CNTs/MF as oxidant to polymerize the pyrrole vapor. Finally, CNTs are coated on the surface of PPy/CNTs/MF to increase the conductivity of the composite (CNTs/PPy/CNTs/MF) by dip‐dry process again. The composites have been characterized by X‐ray diffraction spectroscopy, scanning electron microscopy and electrochemical method. The results show that the structure of the composites has obvious influence on their capacitive properties. According to the galvanostatic charge/discharge test, the specific capacitance of CNTs/PPy/CNTs/MF is about 184 F g^?1 based on the total mass of the composite and 262 F g^?1 based on the mass of PPy (70.2 wt % in the composite) at the current density of 0.4 A g^?1, which is higher than that of PPy/CNTs/MF (120 F g^?1 based on the total mass of the composite and 167 F g^?1 based on the mass of the PPy). Furthermore, the capacitor assembled by CNTs/PPy/CNTs/MF shows excellent cyclic stability. The capacitance of the cell assembled by CNTs/PPy/CNTs/MF retains 96.3% over 450 scan cycles at scan rate of 20 mV s^?1, which is larger than that assembled by CNTs/PPy/MF (72.5%). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39779.     

Fabrication and electrochemical properties of carbon nanotube film electrodes

Carbon nanotube (CNT) film electrodes were fabricated by a novel process involving the electrostatic spray deposition (ESD) of a CNT solution. Acid treated CNTs were dispersed in an aqueous solvent through sonication and then the CNT solution was electrostatically sprayed onto a metallic substrate by the ESD method. The CNT film electrodes showed well-entangled and interconnected porous structures with good adherence to the substrate. A specific capacitance of 108 F/g was achieved for the electrodes in 1 M H₂SO₄. In addition, the CNT film electrode showed good high rate capability.     

Preparation and electrochemical properties of polyaniline doped with benzenesulfonic functionalized multi-walled carbon nanotubes

Nanocomposite of benzenesulfonic functionalized multi-walled carbon nanotubes doped polyaniline (PANi/f-MWCNTs) was synthesized via a low-temperature in situ polymerization method. The PANi/f-MWCNTs composite has a thin film of PANi coating uniformly on the surface of the f-MWCNTs. The electrochemical results show that PANi/f-MWCNTs nanocomposite possesses good rate response, which could ascribe to the uniform structure and the better conductivity of composite as well as the in situ doping/de-doping process between the benzenesulfonic acid groups of f-MWCNTs and PANi chain. In addition, the composite also has better capacity and cyclability than PANi/p-MWCNTs composite. It could attribute to the presence of f-MWCNTs, which makes more electrolyte contact with PANi to participate in faradaic redox reactions and dopes with the PANi polymer chain through the benzenesulfonic acid groups to form stable polyemeraldine salts.     

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.     

Lithium storage performance of carbon nanotubes prepared from polyaniline for lithium-ion batteries

Carbon nanotubes with large surface area and surface nitrogen and oxygen functional groups are prepared by carbonizing and activating of polyaniline nanotubes, which is synthesized by polymerization of aniline with the self-assembly method in aqueous media. The physicochemical properties of the carbon nanotubes are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, elemental analyses and X-ray photoelectron spectroscopy measurements. The surface area and pore diameter are 618.9 m² g⁻¹ and 3.10 nm. The electrochemical properties of the carbon nanotubes as anode materials in lithium ion batteries are evaluated. At a current density of 100 mA g⁻¹, the activated carbon nanotube shows an enormously first discharge capacity of about 1370 mAh g⁻¹ and a charge capacity of 907 mAh g⁻¹. After 20 cycling tests, the activated carbon nanotube retains a reversible capacity of 728 mAh g⁻¹. These indicate it may be a promising candidate for an anode material for lithium secondary batteries.     

TiC-modified carbon nanotubes,TiC nanotubes and TiC nanorods: Synthesis and characterization

In the present study, single-phase TiC nanotubes and nanorods were synthesized by a novel pressureless spark plasma sintering (SPS) technique using carbon nanotubes (CNTs) and titanium powders at 1050?°C for 5?min. Moreover, formation mechanism of the resultant nanomaterials was clarified in detail. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) patterns and Raman spectroscopy were conducted to study the microstructure and nature of the produced samples. XRD patterns indicated that all powders reacted to form TiC after applying 1050?°C. In addition, according to the TGA results, a significant increment in thermal properties was achieved compared to the pristine CNTs.     

Capacitance properties of multi-walled carbon nanotubes modified by activation and ammoxidation

Catalytic multi-walled carbon nanotubes were modified by KOH activation at 800 °C and/or ammoxidation at 350 °C, and the effect of these treatments on the physicochemical and electrochemical properties was investigated. Whereas texture is moderately changed by ammoxidation, the chemical composition is significantly modified due to the formation of various nitrogen containing groups. The influence of nitrogenated functionality (pyridine, pyridone, NH) on charge accumulation is considered in full electrochemical capacitors, as well as in positive and negative electrodes separately, using acidic (4 mol L⁻¹ H₂SO₄) and alkaline (7 mol L⁻¹ KOH) electrolytes. The presence of nitrogen in the carbon network, especially in the form of pyridone/pyrrolic (N5) and/or pyridine (N6) groups, affects the electron density and enhances the charge affinity of the carbon material. It seems that the nitrogen groups improve particularly the capacitance performance of the negative electrode operating in alkaline medium. Besides the nitrogenated groups, the oxygenated functionality plays also an important role for the ammoxidized nanotubes. Generally, a few-fold increase of capacitance was observed in the N-enriched carbon nanotubular samples. Apart of this capacitance improvement, the presence of nitrogen in the carbon network limits significantly the leakage current and diminishes the self-discharge of supercapacitors.     

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.     

The effect of electrolytic oxidation on the electrochemical properties of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWNTs) were electrochemically oxidized by a constant-potential electrolysis method and then investigated in detail using scanning electron microscope, transmission electron microscope, FT-IR, electrical impedance spectroscopy, and cyclic voltammetry. The FT-IR spectra showed that the amount of hydroxyl generated on the surface of MWNTs increased with increasing the electrochemical oxidation time of MWNTs. The CV results, being conducted in nitrobenzene solution, showed that the nitrobenzene reduction current increased with the increase in oxidation time of the MWNTs within the first 60 min of electrolysis. An electrical equivalent circuit model for electrical impedance spectroscopy was further established to analyze the surface capacitance and resistance of the MWNTs, and the model results showed that the capacitance of the oxidized MWNTs increased greatly while the charge transfer resistance decreased, suggesting electrochemical oxidized MWNTs modified pyrolytic carbon electrode being an effective electrochemical sensor for nitrobenzene determination.     

High power density electrodes for Carbon supercapacitor applications

This paper presents results obtained with 4 cm² Carbon/Carbon supercapacitors cells in organic electrolyte. In the first approach, a surface treatment for Al current collector foil via the sol-gel route has been used in order to decrease the Al/active material interface resistance. Performances obtained with this original process are: a low equivalent series resistance (ESR) of 0.5 Ω cm² and a specific capacitance of 95 F g⁻¹ of activated carbon.Then, supercapacitors assembled with treated Al foil and active material containing activated carbon/carbon nanotubes (CNTs) with different compositions have been studied. Galvanostatic cycling measurements show that when CNTs content increases, both ESR and specific capacitance are decreased. Fifteen percent appears to be a good compromise between stored energy and delivered power with an ESR of 0.4 Ω cm² and a specific capacitance of 93 F g⁻¹ of carbonaceous active material.Finally, cells frequency behaviour has been characterized by Electrochemical Impedance Spectroscopy. The relaxation time constant of cells decreases when the CNTs content increases. For 15% of CNTs, the time constant is about 30% lower as compared to a cell using pure activated carbon-based electrodes leading to a higher delivered power.     

Feasibility of bamboo-based activated carbons for an electrochemical supercapacitor electrode

This study focused on the preparation and electrochemical properties of bamboo-based activated carbons (ACs) through carbonization and subsequent activation with steam and non-aqueous electrolyte solutions. The specific surface areas and the capacitances of samples ranged from 445 to 1,025 m²/g and from 5 to 60 F/g, respectively, depending on the activation conditions. The sample activated at 900 ‡C for 60 min under our experimental conditions exhibited the highest capacitance and the largest specific surface area.     

In situ electrochemical preparation of multi-walled carbon nanotubes/polyaniline composite on the stainless steel

Polyaniline–carbon nanotubes (PANI–CNTs) composites have been deposited via in situ electropolymerization on stainless steel (SS) surface. The presence of the oxidized multi-walled carbon nanotubes (mCNTs) in the composite was confirmed by thermal gravimetric analysis (TGA) and scanning electron microscope. Introducing 28 and 70 mg L⁻¹ mCNT in the electrolyte increased the growth rate of PANI from 38 to 67 and 83 mC/cycle, respectively. The mCNT decreases the porosity of the PANI, forming networks which held the polymer. Influences of the composite layer on the passivation and corrosion of the stainless steel were studied and compared with pure PANI layer. It was confirmed that a higher resistant passive film was formed on the steel under the composite layer compared to that formed under the pure PANI.     

Fabrication and electrochemical characterization of polyimide-derived carbon nanofibers for self-standing supercapacitor electrode materials

We report the electrochemical performance of aromatic polyimide (PI)-based carbon nanofibers (CNFs), which were fabricated by electrospinning, imidization, and carbonization process of poly(amic acid) (PAA) as an aromatic PI precursor. For the purpose, PAA solution was electrospun into nanofibers, which were then converted into CNFs via one-step (PAA-CNFs) or two-step heat treatment (PI-CNFs) of imidization and carbonization. The FTIR and Raman spectra demonstrated a successful structural evolution from PAA nanofibers to PI nanofibers to CNFs at the molecular level. The SEM images revealed that the average diameter of the nanofibers decreased noticeably via imidization and carbonization, while it decreased slightly with increasing the carbonization temperature from 800 °C to 1000 °C. In case of PI-CNF carbonized at 1000 °C, a porous structure was developed on the surface of nanofibers. The electrical conductivity of PI-CNFs, which was even higher than that of PAA-CNFs, increased significantly from 0.41 to 2.50 S/cm with increasing the carbonization temperature. From cyclic voltammetry and galvanostatic charge/discharge tests, PI-CNF carbonized at 1000 °C was evaluated to have a maximum electrochemical performance of specific capacitance of ~126.3 F/g, energy density of ~12.2 Wh/kg, and power density of ~160 W/kg, in addition to an excellent operational stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47846.