Facile synthesis of graphene/polyaniline composite hydrogel for high-performance supercapacitor

The graphene/polyaniline (PANI) composite hydrogel was successfully prepared by a one-step hydrothermal method. The morphology and structure of the sample were characterized by digital camera, scanning electron microscopy, and Fourier transform infrared spectroscopy spectra. By combining the advantages of high conductivity of graphene and high pseudocapacitance of PANI, the composite hydrogel was taken as supercapacitor electrode material. Cyclic voltammetry and galvanostatic charge/discharge experimental results show that the composite has excellent electrochemical performance. The specific capacitance value is 258.5 F g^?1 at a scan rate of 2 mV s^?1 and the specific capacitance value is up to 307 F g^?1 at a current density of 0.2 A g^?1. The specific capacitance value can still maintain 90 % of the initial value after repeating the galvanostatic charge–discharge for 1000 cycles at a current density of 1.0 A g^?1 showing good cycle stability.     

Pore-size-tunable nitrogen-doped polymeric frameworks for high performance sodium ion storage and supercapacitors

Sodium-ion batteries (SIBs) is considered as a promising alternative to lithium-ion batteries. Supercapacitors (SCs) are receiving great attention for their significantly higher power density than batteries and prolonged cycle life. Herein, SIBs and SCs based on N-doped amorphous multi-size pores dominated polymeric frameworks were fabricated and examined. The enlarged interlayer spacing and multi-size-pore dominated interconnected architecture with high specific surface area, high pore volume and high N content optimize the electrochemical performance of N-PPF-20. As an anode material, N-PPF-20 exhibited a sodium ion storage capacity of 432.2 mAh g^?1 at a current density of 0.05 A g^?1, while maintaining a reversible capacity of 61.1 mAh g^?1 at an ultrahigh current density of 20 A g^?1. Additionally, a specific capacity of 158.3 mAh g^?1 at 1 A g^?1 was obtained after 1000 cycles, indicating an excellent cycling stability. When tested as an electrode material for SCs, N-PPF-20 delivered a high specific capacitance of 438.7 F g^?1 at 0.1 A g^?1, and a specific capacitance of 111.2 F g^?1 was achieved even at a high current density of 10 A g^?1. Meanwhile, a long-term cycling life test demonstrated a specific capacitance of 120 F g^?1 at an ultrahigh current density of 10 A g^?1 after 10,000 cycles.     

Graphene/Polyaniline Aerogel with Superelasticity and High Capacitance as Highly Compression-Tolerant Supercapacitor Electrode

Superelastic graphene aerogel with ultra-high compressibility shows promising potential for compression-tolerant supercapacitor electrode. However, its specific capacitance is too low to meet the practical application. Herein, we deposited polyaniline (PANI) into the superelastic graphene aerogel to improve the capacitance while maintaining the superelasticity. Graphene/PANI aerogel with optimized PANI mass content of 63 wt% shows the improved specific capacitance of 713 F g^?1 in the three-electrode system. And the graphene/PANI aerogel presents a high recoverable compressive strain of 90% due to the strong interaction between PANI and graphene. The all-solid-state supercapacitors were assembled to demonstrate the compression-tolerant ability of graphene/PANI electrodes. The gravimetric capacitance of graphene/PANI electrodes reaches 424 F g^?1 and retains 96% even at 90% compressive strain. And a volumetric capacitance of 65.5 F cm^?3 is achieved, which is much higher than that of other compressible composite electrodes. Furthermore, several compressible supercapacitors can be integrated and connected in series to enhance the overall output voltage, suggesting the potential to meet the practical application.     

A redox‐mediator‐doped gel polymer electrolyte applied in quasi‐solid‐state supercapacitors

Methylene blue (MB) redox mediator was introduced into polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) blend host to prepare a gel polymer electrolyte (PVA‐PVP‐H₂SO₄‐MB) for a quasi‐solid‐state supercapacitor. The electrochemical properties of the supercapacitor with the prepared gel polymer electrolyte were evaluated by cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy, and self‐discharge measurements. With the addition of MB mediator, the ionic conductivity of gel polymer electrolyte increased by 56% up to 36.3 mS·cm^?1, and the series resistance reduced, because of the more efficient ionic conduction and higher charge transfer rate, respectively. The electrode specific capacitance of the supercapacitor with PVA‐PVP‐H₂SO₄‐MB electrolyte is 328 F·g^?1, increasing by 164% compared to that of MB‐undoped system at the same current density of 1 A·g^?1. Meanwhile, the energy density of the supercapacitor increases from 3.2 to 10.3 Wh·kg^?1. The quasi‐solid‐state supercapacitor showed excellent cyclability over 2000 charge/discharge cycles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39784.     

The effect of halide ion concentration on capacitor performance

The effect of halide ion concentration on the capacitor performance was considered during this study. Iodide anion has been selected as the most profitable halide taking into account its electrochemical properties and environmental impact. Several concentrations of NaI were tested (from 0.25 to 5 mol L^?1 aqueous solutions) using as electrodes two commercial activated carbons and one KOH-activated carbon. Detailed electrochemical investigation by galvanostatic charging/discharging, cyclic voltammetry, and impedance spectroscopy confirmed the significant impact of iodide concentration on the supercapacitor behavior. The higher concentration of iodide affected especially the performance of positive electrode; increase of iodide concentration changed the potential range of positive electrode and its capacitance increased from 119 F g^?1 for 0.25 mol L^?1 NaI to 475 F g^?1 for 2 mol L^?1 NaI solution. The electrode capacitance measured in two-electrode system at current density of 2 A g^?1 ranged from 198 F g^?1 for 0.25 mol L^?1 NaI to 272 F g^?1 for 2 mol L^?1 NaI solution (capacitance expressed as average of the positive and negative electrode capacitances). It has been proved that 2 mol L^?1 alkali metal iodide solution is an optimal electrolyte for the capacitor based on KOH-activated carbon. High capacitance values and perfect stability (100 % retention) of such systems have been observed during long-term galvanostatic charging/discharging (15,000 cycles). In addition, satisfactory floating tests at extended voltage range (1.2 V) were performed.     

Improved electrochemical performances of polyaniline by graphitized mesoporus carbon: Hybrid electrode for supercapacitor

In this work, graphitized mesoporus carbon (GMC) was used to increase the specific capacitance and cycle stability of polyaniline (PANI). Hybrid material of polyaniline‐graphitized mesoporus carbon (GMCP) was prepared by in situ chemical polymerization of aniline in presence of sulphuric acid using ammonium persulfate oxidant with various amounts of GMC. Formation of hybrid sample was confirmed from X‐ray diffraction, and the composite sample was stable up to 250°C. Morphology, crystalline nature, and electrochemical performance of GMCP were compared with that of its individual components, GMC and PANI. GMC showed particle morphology and PANI showed nanofiber morphology. GMCP2 composite showed nanofibrous form of PANI grown on GMC (spherical form) along with PANI nanofibers. Higher crystallinity was obtained for GMCP than that of PANI. Cycling stability of GMCP2 was carried up to 12,000 cycles at 1200 W kg^?1 and the retention capacitance was 66% of its original capacitance of 243 F g^?1. With the same power density, GMC showed less capacitance value of 53 F g^?1 with 92% retention and PANI showed capacitance of 187 F g^?1 and it underwent 1500 cycles only. Higher supercapacitor performance was obtained for GMCP composite compared to that of its components, PANI and GMC. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42540.     

Fabrication of the nitrogen doped ordered porous carbon derived from amino-maltose with excellent capacitance performance

In this paper, pristine and nitrogen doped ordered porous carbon materials were fabricated by using maltose and amino-maltose synthesized by hydrothermal reaction as precursors via template strategy. The fabricated pristine ordered porous carbon (OPC) and nitrogen doped ordered porous carbon (NOPC) exhibit excellent textural properties and good capacitance performance, which specific surface area (S_BET) reach 1107 and 726 m² g^?1 for the pristine OPC and NOPC materials while the specific capacitance reach up to 139 and 183 F g^?1 under a current density of 0.5 A g^?1, respectively. The capacitance retention rate for the pristine OPC and NOPC reaches ca. 81 and 92% as the current density increased from 0.5 to 20 A g^?1, and no apparent capacitance decrease was observed after 5000 cycles. Although a sharp decrease of specific surface area was observed after N doping, the specific capacitance of NOPC was improved about 31% than that of the pristine OPC, the enhanced wettability and surface availability after N doping were found to be responsible for the enhanced capacitance performance of NOPC.     

Controllable growth of Bi2O3 with rod-like structures via the surfactants and its electrochemical properties

This paper reports a systematic study of the synthesis of rod-like Bi₂O₃ via a facile one-step precipitation method with the addition of different surfactants. The formation mechanisms for the surfactants assisted chemical precipitation method of rod-like Bi₂O₃ have been briefly discussed. The electrochemical measurement shows the Bi₂O₃ prepared by using P123 as surfactant exhibits the largest specific capacitance of 1,350 F g^?1 at current density of 0.1 A g^?1 as well as superior rate capability and excellent cycle stability. The scalable syntheses and prominent capacitive properties of this material suggest its potential applications in energy storage.     

Graphite oxide/polypyrrole composite electrodes for achieving high energy density supercapacitors

Fabrication and characterization of high energy density supercapacitor based on graphite oxide/polypyrrole (GO/PPy) composites is reported. Improvement in charge storage has been obtained by exfoliation of graphite oxide sheets via intercalation of polypyrrole. The formation of composite has been shown by the analysis of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transfer of infrared spectroscopy data. Scanning electron and transmission electron microscopy clearly show sheet-like layered structure of graphite oxide surrounded by polypyrrole. Supercapacitors fabricated using this composite system result in a reduced equivalent series resistance value ~1.85 Ω. Such low value can be attributed to the intercalation of conducting polypyrrole into the graphite sheets. A specific capacitance of ~181 F g^?1 in 1 M Na₂SO₄ aqueous electrolyte with a corresponding specific energy density of ~56.5 Wh kg^?1 could be achieved. These values make GO-based materials suitable for their use as electrodes in high performance supercapacitors.     

Preparation and molten salt-assisted KOH activation of porous carbon nanofibers for use as supercapacitor electrodes

Carbon nanofiber paper was prepared by electrospinning from thermosetting phenolic resin, followed by activation via KOH-containing molten salt at high temperature. By adding a small dosage of KOH in the molten salt the porous volume and specific surface area could be greatly improved. The obtained porous carbon nanofibers had a specific surface area of 1007 m² g^?1, total pore volume of 0.363 cm³ g^?1, micropore volume of 0.247 cm³ g^?1. The electrochemical measurements in 6 M KOH aqueous solution showed that the porous carbon nanofibers possessed high specific capacitance and considerable rate performance. The maximal specific capacitance of 288 F g^?1 was achieved at 0.2 A g^?1 and the specific capacitance could still remain 204 F g^??1 at 20 A g^?1 with the retention of 71%. In the molten salt system, the reaction between activating agent and carbon could be more efficient, hence, such molten salt-assisted activation method was considered as a general activation method for the high-specific-surface-areaed carbons.     

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).     

MnO2 depositing on the surface of hollow porous carbon microspheres for supercapacitor application

A supercapacitor electrode material was synthesized by using hollow carbon spheres prepared via high temperature sintering of dopamine hydrochloride and subsequent coating with MnO₂. SEM, TEM and analysis of energy pattern were used to characterize the structure, morphology and elemental composition of the material, which proved that the material had a good hollow structure and uniform surface morphology, and that MnO₂ was successfully coated on the surface of the carbon material. Electrochemical characterization using charge-discharge cycles at constant current and other methods show that the prepared materials have good specific capacitance and cycle stability, and have a specific capacitance of 198 F.g^?1 at a current of 1 A·g^?1. When the charge and discharge cycle is carried out at 10 A·g^?1 for 5000 cycles, the capacitance remains stable at more than 180 F·g^?1.     

Recent Advances in Electrochemical Performances of Graphene Composite (Graphene-Polyaniline/Polypyrrole/Activated Carbon/Carbon Nanotube) Electrode Materials for Supercapacitor: A Review

The latest trend in the direction of miniaturized portable electronic devices has brought up necessitate for rechargeable energy sources. Among the various non conventional energy devices, the supercapacitor is the promising candidate for gleaning the energy. Supercapacitor, as a new energy device that colligates the gap between conventional capacitors and batteries, it has attracted more attention due to its high power density and long cycle life. Many researchers work on, synthesizing new electrode material for the development of supercapacitor. The electrode material possesses salient structure and electrochemical properties exhibit the efficient performance of the supercapacitor. Graphene has high carrier mobility, thermal conductivity, elasticity and stiffness and also has a theoretical specific capacitance of 2630 m²g^??1 corresponds to a specific capacitance of 550 Fg^??1. This article summarizes and reviews the electrochemical performance and applications of various graphene composite materials such as graphene/polyaniline, graphene/polypyrrole, graphene/metal oxide, graphene/activated carbon, graphene/carbon nanotube as an electrode materials towards highly efficient supercapacitors and also dealt with symmetric, asymmetric and hybrid nature of the graphene based supercapacitor.     

Nanosheet-like MoO3 and conductive PANI electrodeposited on flexible carbon cloth for self-supported solid-state supercapacitor electrode

In this paper, uniformly transition metal oxide (MoO₃) nanosheets were electrochemically deposited on flexible carbon cloth (CC), and then conductive polyaniline (PANI) was orderly wrapped around their surface by electrochemical polymerization. The morphology and structure of as-obtained self-supported PANI/MoO₃/CC electrode were investigated by FTIR, X-ray diffraction, Raman, scanning electron microscope (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy measurements in detail. Among all PANI/MoO₃/CC electrode, the self-supported PMC-3 (deposition time of 300 s) has high specific capacitance of 841.6 F g⁻¹ at current density of 0.5 A g⁻¹ in the three-electrode system, having specific capacitance of 595.7 F g⁻¹ even at 10 A g⁻¹. Novelty, the as-assembled symmetrical capacitor is flexible and convenient with power density of 199.93 W kg⁻¹ at the energy density of 9.69 Wh kg⁻¹ and the energy density of 3.88 Wh kg⁻¹ at power density of 4000 W kg⁻¹. Thus, the electrochemical properties of the self-supported PANI/MoO₃/CC electrode were significantly improved, and the self-supported electrodes are more competitive than other materials in practical application of clean energy storage systems.     

KOH-activated depleted fullerene soot for electrochemical double-layer capacitors

Nanostructured activated carbons for electrochemical double-layer capacitors were synthesized from depleted fullerene soot (DFS) via KOH activation. The structural and textural properties of the activated DFS were studied using transmission electron microscopy, X-ray diffraction, and nitrogen sorption. Activated DFS with high specific surface areas (SSAs) of up to 2,153 m² g^?1 and narrow pore size distributions (PSDs) was obtained by controlling the KOH/DFS ratio. The activated DFS exhibited excellent capacitive behavior, with a high specific capacitance of 250 F g^?1 at a current density of 50 mA g^?1 in a 6 M KOH electrolyte, and a high rate performance, with a capacitance retention of up to 80 % at a high scan rate of 200 mV s^?1. Moreover, the activated DFS samples exhibited good electrochemical stability; high capacitance retention ratios of >90 % were obtained at a current density of 2,000 mA g^?1 for 5,000 cycles with cell voltages of 0.9 and 1.0 V in a two-electrode system. The high electrochemical performance can be attributed to high SSAs, narrow PSDs, and nanoscale particle sizes, which facilitate the formation of electrochemical double layers and rapid ion diffusion.     

In situ doping of PANI nanocomposites by gold nanoparticles for high‐performance electrochemical energy storage

Polyaniline (PANI) in situ doped with gold nanoparticles (Au/PANI) is synthesized by oxidative polymerization as electrode material for supercapacitor. The morphologies and structure of the obtained products are characterized by transmission electron microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy; and electrochemical behaviors were measured by electrochemical workstation. The results show that the nanocomposites of Au/PANI are fabricated with gold nanoparticles (nano‐Au) dispersed well in PANI bulk; and specific capacitance (SC) and rate ability of Au/PANI are improved compared to the pristine PANI due to the introduction of nano‐Au. With nano‐Au content increasing, SC first increase and then decrease and the maximum SC of Au/PANI nanocomposite is up to 462 F g^?1 with the nano‐Au content of 1.64 wt %. Finally, both asymmetric and symmetric supercapacitor devices are assembled, exhibiting high energy densities of 8.95 and 4.17 Wh kg^?1, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45309.     

Enhanced capacitance of a NiO electrode prepared in the magnetic field

The enhancement of the surface alignment by magnetic field had a great theoretical and practical significance in the improvement of electrochemical capacitor. In the present study, the NiO nanowires were synthesized by liquid-phase reduction method, and the electrode was prepared within external magnetic field. The effects of magnetic field on the electrode surface and the electrochemical behavior were investigated. X-ray diffraction and scanning electron microscope studies showed that the applied magnetic field results in an orderly surface structure of the electrode, which induced an effective transfer path for the electrons and ions. Meanwhile, the orderly electrode surface improved the electrochemical capacitance, as well as decreased the internal resistance. It was found on the cyclic voltammetry and galvanostatic charge/discharge measurements that the electrode prepared with the magnetic field displays an increased capacitance (506 F g^?1), high power density (135.8 W kg^?1) and energy density (17.6 Wh kg^?1), and improved cycle stability compared to the electrode without magnetic field. Electrochemical impedance spectroscopy results demonstrated enhanced electrochemical properties for the addition of magnetic field.     

A new route to synthesize polyaniline-grafted carboxyl-functionalized graphene composite materials with excellent electrochemical performance

A new route to synthesize polyaniline (PANI)-grafted carboxyl-functionalized graphene (PGCG) composite material is established. In this paper, PGCG is first prepared through a two-step carboxyl-functionalized process. PANI can be grafted and grown on the surface of graphene due to the covalent bonding existing between the carboxyl-functionalized graphene and polyaniline. This method cannot only improve the mechanical performance and adaptive performance of polyaniline effectively, but also reduce the production costs and environmental pollution during the synthetic process. Therefore, a green and industrial synthetic process is achieved. X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FTIR) all confirm that composite materials have been prepared successfully. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate that the as-prepared PGCG has regular structure. Thermogravimetric analysis (TGA) indicates that the addition of graphene nanosheets can significantly improve the thermostability of PANI. Moreover, the as-prepared material exhibits superior electrochemical performance. As an electrode material for supercapacitors, PGCG possesses high specific capacitance of 158 F g^?1 at a scan rate of 25 mV s^?1 and 147 F g^?1 at 50 mV s^?1 in 1 M H₂SO₄. The Nyquist plot also confirms that the PGCG has low charge transfer resistance and good capacitive behavior. These great properties make PGCG a novel electrode material with potential applications in high-performance energy storage devices.     

Polyaniline/MnO2 composite with high performance as supercapacitor electrode via pulse electrodeposition

A method of pulse electrodeposition was proposed to synthesize polyaniline (PANI)/MnO₂ composite in aniline, H₂SO₄, and MnSO₄ aqueous solution. The PANI/MnO₂ composite has rod‐like structure and MnO₂ particles are distributed on PANI uniformly. To evaluate the performance of the as‐prepared materials as supercapacitor electrodes, cyclic voltammetry, galvanostatic charge–discharge measurements, and electrochemical impedance spectroscopy were performed. The PANI/MnO₂ composite shows a higher specific capacitance (810 F g⁻¹) than pure PANI (662 F g⁻¹) at a current density of 0.5 A g⁻¹. The cycle life of the composite was also excellent. After 1,000 cycles, it maintained 86.3% of its initial capacitance. POLYM. COMPOS., 36:113–120, 2015. © 2014 Society of Plastics Engineers     

Enhanced performance by polyaniline/tailored carbon nanotubes composite as supercapacitor electrode material

Polyaniline/tailored carbon nanotubes composite (PANI/TCN) synthesized via situ polymerization of aniline monomer in the presence of tailored carbon nanotubes (TCN) is reported as electrode material for supercapacitors. The morphology, structure, and thermostability of the composite were characterized by scanning electron microscope, Fourier transform infrared, and thermogravimetric analysis. The electrochemical property of the resulting material was systematically studied using cyclic voltammetry and galvanostatic charge–discharge. The results show that the short rod‐like PANI dispersed well in the TCN with three‐dimensional network structure. The as‐prepared composite shows high specific capacitance and good cycling stability. A specific capacitance of 373.5 F g^?1 at a current density of 0.5 A g^?1 was achieved, which is much higher than that of pure PANI (324 F g^?1). Meanwhile, the composite retains 61.7% capacity after 1000 cycles at a scan rate of 50 mV s^?1. The enhanced specific capacitance and capacity retention indicates the potential of composite as a promising supercapacitor electrode material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39971.