Electrochemical properties of graphene nanosheets/polyaniline nanofibers composites as electrode for supercapacitors

Graphene nanosheets/polyaniline nanofibers (GNS/PANI) composites are synthesized via in situ polymerization of aniline monomer in HClO₄ solution. The PANI nanofibers homogeneously coating on the surface of GNS greatly improve the charge transfer reaction. The GNS/PANI composites exhibit better electrochemical performances than the pure individual components. A remarkable specific capacitance of 1130 F g⁻¹ (based on GNS/PANI composites) is obtained at a scan rate of 5 mV s⁻¹ in 1 M H₂SO₄ solution compared to 402 F g⁻¹ for pure PANI and 270 F g⁻¹ for GNS. The excellent performance is not only due to the GNS which can provide good electrical conductivity and high specific surface area, but also associate with a good redox activity of ordered PANI nanofibers. Moreover, the GNS/PANI composites present excellent long cycle life with 87% specific capacitance retained after 1000 charge/discharge processes. The resulting composites are promising electrode materials for high-performance electrical energy storage devices.     

Enhanced capacitance and rate capability of graphene/polypyrrole composite as electrode material for supercapacitors

Graphene and polypyrrole composite (PPy/GNS) is synthesized via in situ polymerization of pyrrole monomer in the presence of graphene under acid conditions. The structure and morphology of the composite are characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), X-rays photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). It is found that a uniform composite is formed with polypyrrole being homogeneously surrounded by graphene nanosheets (GNS). The composite is a promising candidate for supercapacitors to have higher specific capacitance, better rate capability and cycling stability than those of pure polypyrrole. The specific capacitance of PPy/GNS composite based on the three-electrode cell configuration is as high as 482 F g⁻¹ at a current density of 0.5 A g⁻¹. After 1000 cycles, the attenuation of the specific capacitance is less than 5%, indicating that composite has excellent cycling performance.     

Electrochemical properties of leucoemeraldine, emeraldine, and pernigraniline forms of polyaniline/multi-wall carbon nanotube nanocomposites for supercapacitor applications

We report on the synthesis and electrochemical properties of leucoemeraldine base, emeraldine salt and pernigraniline base forms of polyaniline (PANI) in the form of nanocomposites with MWNTs. The oxidation state of PANI in the composite is controlled by doping and dedoping of the emeraldine salt form of PANI/MWNT composite, which is prepared through chemical polymerization, using oxidizing and reducing agents without changing the morphology of PANI in the composite and is confirmed by ultraviolet-visible spectroscopy (UV-vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical and pseudocapacitive properties of the composites are investigated using cyclic voltammetry and analyzed with respect to the oxidation state of polyaniline. The PANI/MWNT nanocomposites show specific capacitance values of 217 F g⁻¹, 328 F g⁻¹ and 139 F g⁻¹ for leucoemeraldine base, emeraldine salt and pernigraniline base, respectively. Electrochemical impedance spectroscopy is performed to explain the different electrochemical properties of PANI in different oxidation states.     

Electrodeposition and pseudocapacitive properties of tungsten oxide/polyaniline composite

Composite films of tungsten oxide (WO₃) and polyaniline (PANI) have been electrodeposited by cyclic voltammetry in a mixed solution of aniline and precursor of tungsten oxide. Surface morphology and chemical composition of WO₃/PANI composite are characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of H₂O₂ on the electrodeposition of WO₃/PANI composite film is also investigated. Cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) results show that WO₃/PANI composite film exhibit good pseudocapacitive performance over a wide potential range of −0.5 to 0.7 V vs. SCE with the specific capacitance of 168 F g⁻¹ at current density of 1.28 mA cm⁻² and energy density of 33.6 Wh kg⁻¹, which is 91% higher than that of similarly prepared PANI (17.6 Wh kg⁻¹). An asymmetric model capacitor using WO₃/PANI as negative and PANI as positive electrodes over voltage range of 1.2 V displays a specific capacitance of 48.6 F g⁻¹ and energy density of 9.72 Wh kg⁻¹ at the power density of 53 W kg⁻¹, which is two times higher than that of a symmetric capacitor modeled by using two PANI films as both positive and negative electrodes.     

The preparation and performance of calcium carbide-derived carbon/polyaniline composite electrode material for supercapacitors

Calcium carbide (CaC₂)-derived carbon (CCDC)/polyaniline (PANI) composite materials are prepared by in situ chemical oxidation polymerization of an aniline solution containing well-dispersed CCDC. The structure and morphology of CCDC/PANI composite are characterized by Fourier infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM) and N₂ sorption isotherms. It has been found that PANI was uniformly deposited on the surface and the inner pores of CCDC. The supercapacitive behaviors of the CCDC/PANI composite materials are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge and cycle life measurements. The results show that the CCDC/PANI composite electrodes have higher specific capacitances than the as grown CCDC electrodes and higher stability than the conducting polymers. The capacitance of CCDC/PANI composite electrode is as high as 713.4 F g⁻¹ measured by cyclic voltammetry at 1 mV s⁻¹. Besides, the capacitance retention of coin supercapacitor remained 80.1% after 1000 cycles.     

Construction of composite electrodes comprising manganese dioxide nanoparticles distributed in polyaniline-poly(4-styrene sulfonic acid-co-maleic acid) for electrochemical supercapacitor

This work demonstrated a novel and simple route for preparing a composite comprising of manganese oxide (MnO₂) nanoparticles and polyaniline (PANI) doped poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) by “electrochemical doping-deposition”. The PANI-PSSMA-MnO₂ composite was characterized by scanning electron microscopy (SEM)), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). SEM images revealed a uniform dispersion of MnO₂ nanoparticles in the porous structure of PANI-PSSMA structure. XRD measurements showed the distortion of the crystal structure of β-MnO₂ after deposition of MnO₂ in PANI-PSSMA structure. Thus, the XRD pattern of PANI was predominating. Cyclic voltammetry and chronopotentiometry were employed in 0.5 M Na₂SO₄ to evaluate the capacitor properties. The results showed a significant improvement in the specific capacitance of the composite electrode. The specific capacitance of PANI-PSSMA-MnO₂ (50.4 F g⁻¹) had improvement values of 172% compared to that of PANI (18.5 F g⁻¹). When only the MnO₂ mass was considered, the composite had a specific capacitance of 556 F g⁻¹.     

Electrodeposition of manganese dioxide in three-dimensional poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline for supercapacitor

The preparation of composites of precise metal oxides/conducting polymers is important in studies of supercapacitors. In this work, a three-dimensional matrix of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid)–polyaniline (PEDOT–PSS–PANI) was prepared by interfacial polymerization of ANI into PEDOT–PSS. Conductivity was enhanced by incorporating of PANI into PEDOT–PSS because of the decrease in the distance for electron shuttling along the conjugated polymeric chain. Composite electrodes were prepared by the electrodeposition of manganese dioxide (MnO₂) in a PEDOT–PSS–PANI three-dimensional matrix. The electrodes were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry techniques. The results show a significant improvement in the specific capacitance of the composite electrode. For PEDOT–PSS the specific capacitance was of 0.23 F g⁻¹, while PEDOT–PSS–PANI and PEDOT–PSS–PANI–MnO₂ displayed values of 6.7 and 61.5 F g⁻¹, respectively. When only considering the MnO₂ mass, the composite had the specific capacitance of 372 F g⁻¹. The composite also had an excellent cyclic performance.     

Growth of polyaniline nanowhiskers on mesoporous carbon for supercapacitor application

Vertically aligned polyaniline nanowhiskers (PANI-NWs) doped with (1R)-(−)-10-Camphorsulfonic acid (L-CSA) have been successfully synthesized on the external surface of ordered mesoporous carbon (CMK-3) by chemical oxidative polymerization. The specific surface area of the PANI-NWs/CMK-3 nanocomposite remains as high as 497 m² g⁻¹ by removing mesoporous silica template after the polymerization of aniline. Structural and morphological characterizations of the nanocomposite were further investigated by XRD, FTIR and FE-SEM measurements. The result shows that the nanocomposite with 40 wt% PANI applying in supercapacitor devices possesses a large specific capacitance of 470 F g⁻¹ and good capacitance retention of 90.4% is achieved after 1000 cycles at a current density of 1.0 A g⁻¹. The synergistic effect of small PANI nanowhisker arrays and well-ordered mesoporous carbon endows the composite with high electrochemical capacitance and good cycling stability.     

Electrochemical properties of manganese oxide coated onto carbon nanotubes for energy-storage applications

Birnessite-type manganese dioxide (MnO₂) is coated uniformly on carbon nanotubes (CNTs) by employing a spontaneous direct redox reaction between the CNTs and permanganate ions (MnO₄⁻). The initial specific capacitance of the MnO₂/CNT nanocomposite in an organic electrolyte at a large current density of 1 A g⁻¹ is 250 F g⁻¹. This is equivalent to 139 mAh g⁻¹ based on the total weight of the electrode material that includes the electroactive material, conducting agent and binder. The specific capacitance of the MnO₂ in the MnO₂/CNT nanocomposite is as high as 580 F g⁻¹ (320 mAh g⁻¹), indicating excellent electrochemical utilization of the MnO₂. The addition of CNTs as a conducting agent improves the high-rate capability of the MnO₂/CNT nanocomposite considerably. The in situ X-ray absorption near-edge structure (XANES) shows improvement in the structural and electrochemical reversibility of the MnO₂/CNT nanocomposite after heat-treatment.     

Preparation and enhanced capacitance of core–shell polypyrrole/polyaniline composite electrode for supercapacitors

Polypyrrole (PPy) nanotubes were synthesized by using the complex of methyl orange (MO)/FeCl₃ as a template. Then the core–shell polypyrrole/polyaniline (PPy/PANI) composite was prepared by in situ chemical oxidation polymerization of aniline on the surface of PPy nanotubes. The morphology and molecular structure were characterized by transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). TEM images confirmed that the composite was core–shell nanotubes. The electrochemical properties of the PPy/PANI composite electrode were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The electrochemical experiments showed that the specific capacitance of the PPy/PANI composite was 416 F g⁻¹ in 1 M H₂SO₄ electrolyte and 291 F g⁻¹ in 1 M KCl electrolyte. Furthermore, the composite electrode exhibited a good rate capability and maintained 91% of initial capacity at a current density of 15 mA cm⁻² in 1 M H₂SO₄ electrolyte.     

Supercapacitive properties of polyaniline/Nafion/hydrous RuO2 composite electrodes

Chemically prepared polyaniline is tested for its supercapacitive behaviour in an aqueous electrolyte of 1.0 M H₂SO₄. In order to improve the cycleability of the polyaniline electrode, it is made into a composite with Nafion. This composite electrode shows improved cycleability and higher specific capacitance compared with a pure polyaniline electrode. It is therefore used as a matrix for the electrochemical deposition of hydrous RuO₂. The resulting ternary composite electrode has a high specific capacitance of 475 F g⁻¹ at 100 mV s⁻¹ and 375 F g⁻¹ at 1000 mV s⁻¹ in the voltage range of −0.2 to 0.8 V versus Ag/AgCl. All three types of electrode are characterized by cyclic voltammetry and impedance anaylsis.     

Effect of compounding process on the structure and electrochemical properties of ordered mesoporous carbon/polyaniline composites as electrodes for supercapacitors

Polyaniline (PANI) loaded ordered mesoporous carbon (OMC) composites were prepared via different processes, involving the in situ polymerization of aniline in the presence of OMC or its precursor and the direct physical mixing method. On the basis of analyzing the morphologies and structures of these three OMC/PANI composites, the influence of compounding processes on the electrochemical properties as electrodes for supercapacitors was first investigated. It was observed that regardless of compounding process, two distinct electrochemical behaviors took place on all of the composite electrodes, including a redox reaction with insertion and deinsertion of electrolyte ions, and electrostatic attraction at the electrode/electrolyte interface. Additionally, these OMC/PANI composites showed higher specific capacitances compared with pure OMC and PANI. Most significantly, the in situ synthesized OMC/PANI composite using OMC as a starting material exhibited the highest specific capacitance of 747 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent rate capability, which was attributed to the high degree of dispersion of PANI and the contact of PANI with electrolyte as well as the double fixing effects of surface and mesopore of OMC on PANI.     

Supercapacitive properties of hybrid films of manganese dioxide and polyaniline based on active carbon in organic electrolyte

This is the first report about supercapacitive performance of hybrid film of manganese dioxide (MnO₂) and polyaniline (PANI) in an organic electrolyte (1.0 M LiClO₄ in acetonitrile). In this work, a high surface area and conductivity of active carbon (AC) electrode is used as a substrate for PANI/MnO₂ film electro-codeposition. The redox properties of the coated PANI/MnO₂ thin film exhibit ideal capacitive behaviour in 1 M LiClO₄/AN. The specific capacitance (SC) of PANI/MnO₂ hybrid film is as high as 1292 F g⁻¹ and maintains about 82% of the initial capacitance after 1500 cycles at a current density of 4.0 mA cm⁻², and the coulombic efficiency (η) is higher than 95%. An asymmetric capacitor has been developed with the PANI/MnO₂/AC positive and pure AC negative electrodes, which is able to deliver a specific energy as high as 61 Wh kg⁻¹ at a specific power of 172 W kg⁻¹ in the range of 0-2.0 V. These results indicate that the organic electrolyte is a promising candidate for PANI/MnO₂ material application in supercapacitors.     

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

In this paper, a nickel hydroxide/activated carbon (AC) composite electrode for use in an electrochemical capacitor was prepared by a simple chemical precipitation method. The structure and morphology of nickel hydroxide/AC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that nano-sized nickel hydroxide was loading on the surface of activated carbon. Electrochemical performance of the composite electrodes with different loading amount was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the introduction of a small amount of nickel hydroxide to activated carbon could promote the specific capacitance of a composite electrode. The composite electrodes have good electrochemical performance and high charge–discharge properties. Moreover, when the loading amount of nickel hydroxide was 6 wt.%, the composite electrode showed a high specific capacitance of 314.5 F g⁻¹, which is 23.3% higher than pure activated carbon (255.1 F g⁻¹). Also, the composite electrochemical capacitor exhibits a stable cyclic life in the potential range of 0–1.0 V.     

Electrochemical supercapacitor behavior of Ni3(Fe(CN)6)2(H2O) nanoparticles

Nanosized Ni₃(Fe(CN)₆)₂(H₂O) was prepared by a simple co-precipitation method. The electrochemical properties of the sample as the electrode material for supercapacitor were studied by cyclic voltammetry (CV), constant charge/discharge tests and electrochemical impedance spectroscopy (EIS). A specific capacitance of 574.7 F g⁻¹ was obtained at the current density of 0.2 A g⁻¹ in the potential range from 0.3 V to 0.6 V in 1 M KNO₃ electrolyte. Approximately 87.46% of specific discharge capacitance was remained at the current density of 1.4 A g⁻¹ after 1000 cycles.     

Carbon nanotube/polyaniline composite as anode material for microbial fuel cells

A carbon nanotube (CNT)/polyaniline (PANI) composite is evaluated as an anode material for high-power microbial fuel cells (MFCs). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) are employed to characterize the chemical composition and morphology of plain PANI and the CNT/PANI composite. The electrocatalytic behaviour of the composite anode is investigated by means of electrochemical impedance spectroscopy (EIS) and discharge experiments. The current generation profile and constant current discharge curves of anodes made from plain PANI, 1 wt.% and 20 wt.% CNT in CNT–PANI composites reveal that the performance of the composite anodes is superior. The 20 wt.% CNT composite anode has the highest electrochemical activity and its maximum power density is 42 mW m⁻² with Escherichia coli as the microbial catalyst. In comparison with the reported performance of different anodes used in E. coli-based MFCs, the CNT/PANI composite anode is excellent and is promising for MFC applications.     

Polypyrrole/carbon aerogel composite materials for supercapacitor

Polypyrrole (PPy)/carbon aerogel (CA) composite materials with different PPy contents are prepared by chemical oxidation polymerization through ultrasound irradiation and are used as active electrode material for supercapacitor. The morphology of PPy/CA composite is examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that PPy is deposited onto the surface of CA. As evidenced by cyclic voltammetry, galvanostatic charge/discharge test and EIS measurements, PPy/CA composites show superior capacitive performances to CA, moreover, the results based on cyclic voltammograms show that the composite material has a high specific capacitance of 433 F g⁻¹, while the capacitance of CA electrode is only 174 F g⁻¹. Although the supercapacitor used PPy/CA as active electrode material has an initial capacitance loss due to the instability of PPy, the specific capacitance after 500 cycles stabilizes nearly at a fixed value.     

Effects of the cationic structures of fluorohydrogenate ionic liquid electrolytes on the electric double layer capacitance

Electric double layer capacitance of an activated carbon electrode has been measured for fluorohydrogenate ionic liquids (FHILs) based on five different cations (1,3-dimethylimidazolium (DMIm⁺), 1-ethyl-3-methylimidazolium (EMIm⁺), 1-butyl-3-methylimidazolium (BMIm⁺), 1-ethyl-1-methylpyrrolidinium (EMPyr⁺), and 1-methoxymethyl-1-methylpyrrolidinium (MOMMPyr⁺)) at 25 °C. For all the FHILs, the capacitance increases with increase in charging voltage, and exhibits the maximum value around 2.7 V. The capacitances for FHILs are higher than those for EMImBF₄ or 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEABF₄/PC) in the measured range (1.0 < V < 3.2). For the three imidazolium-based FHILs, the maximum capacitance decreases with increase in the size of the cation in the order, DMIm(FH)_2.3F (178 F g⁻¹) > EMIm(FH)_2.3F (162 F g⁻¹) > BMIm(FH)_2.3F (135 F g⁻¹). On the other hand, the maximum capacitance observed for MOMMPyr(FH)_2.3F (152 F g⁻¹) is larger than that for EMPyr(FH)_2.3F (134 F g⁻¹) in spite of the larger size of MOMMPyr⁺ than EMPyr⁺, which is derived from introduction of the methoxy group. Some FHILs with low melting points exhibit a sufficient capacitance even at −40 °C (64 F g⁻¹ for EMIm(FH)_2.3F).     

Ru oxide supercapacitors with high loadings and high power and energy densities

Supercapacitors with very high energy and power densities have been constructed with hydrous ruthenium oxide powder prepared by a sol–gel method and annealed at 110 °C. Novel features of the capacitors, which improve their performances, are the use of a carbon fibre paper support, a Nafion separator, and Nafion as a binder. 1 M sulfuric acid was employed as the electrolyte. The performances of the supercapacitors were characterized by cyclic voltammetry, impedance spectroscopy and constant current discharging. The interfacial capacitance increased linearly with increasing ruthenium oxide loading to at least 50 mg cm⁻² on each electrode. The gravimetric capacitance of the Ru oxide measure by impedance reached 742 F g⁻¹ (9.66 F cm⁻²) at a loading of 13.0 mg cm⁻², and an interfacial capacitance of 34.9 F cm⁻² (682 F g⁻¹) was obtained at 51.2 mg cm⁻². The average effective series resistance was 0.55 Ω, the electronic resistance of the electrodes was negligible, and their ionic resistances were <0.42 Ω. The average power density for full discharge at 1 A cm⁻² for supercapacitors with 10 mg cm⁻² Ru oxide increased by 39% when 5% Nafion binder was added. The maximum average power density for full discharge was 31.5 W g⁻¹ while the maximum energy density was 31.2 Wh kg⁻¹. At a 1 mA discharge rate a specific capacitance of 977 F g⁻¹ of Ru oxide was obtained.