High charge/discharge rate polypyrrole films prepared by pulse current polymerization

Polypyrrole (PPy) films doped by p-toluenesulfonic (PTS) ion were prepared by pulse current polymerization (PCP PPy) and direct current polymerization (DCP PPy) in aqueous solution. During polymerization of DCP PPy films, the sustained high anodic potentials can result in overoxidation and –CH₂– formation at pyrrole rings, which was confirmed by the FTIR spectroscopy. PCP PPy films exhibited more homogeneous and smoother appearance than DCP PPy films. The apparent diffusion coefficient of PCP PPy films was one order of magnitude bigger than that of DCP PPy films, which was closely correlated with the more ordered structure of PCP PPy films confirmed by XRD. When the scanning rate reached up to 500 mV s^?1, the CV curves of PCP PPy films showed rectangular shape within voltage range of ?0.8 V to +0.8 V. High charge/discharge rate of PCP PPy films can be attributed to well wettability, very small charge transfer resistance, high electronic conductivity and ions apparent diffusion coefficient. After 50,000 charge/discharge cycles, the specific capacitance of PCP PPy films only decreased by 14% at a charge/discharge current of 20 A g^?1 within voltage range of 0–0.4 V.     

Toward a high specific power and high stability polypyrrole supercapacitors

Polypyrrole (PPy) films doped by p-toluenesulfonic (PTS) are prepared by pulse current polymerization (PCP PPy) in aqueous solutions. Cations (H⁺, Li⁺, Na⁺, and K⁺ ions) in working electrolyte solutions have a great influence on the electrochemical properties of PCP PPy films for supercapacitors. In 3 M aqueous chloride solutions, the smaller cations lead to the better electrochemical properties of PCP PPy films. PCP PPy films show ideally capacitive characteristics with a very high specific power of 110.9 kW kg^?1 in 3 M HCl when its specific energy reaches 18.4 Wh kg^?1. PCP PPy films are very stable in 3 M HCl, showing less than 4% decay over 160,000 and 20,000 charge/discharge cycles at current density of 40 A g^?1 within voltage range of 0–0.4 V and 0–0.8 V, respectively. The results of SEM show that many pits and grooves appear on the surface of PPy anode in 3 M KCl after 30,000 cycles, which should be main reason of rapid decay of PPy capacitance in 3 M KCl.     

A flexible capacitor based on conducting polymer electrodes

Flexible electrodes for supercapacitors have been prepared by depositing polypyrrole (PPy) on to a gold-coated PVDF membrane. Specific capacitance values of the order of 380 F g^?1 for PPy/Nafion and 420 F g^?1 for PPy/p-toluenesulfonate were obtained. For the PPy/Nafion electrode, an energy density of 56 Wh kg^?1 and a power density of 15.50 kW kg^?1 were available after 5000 cycles.Using a self-contained fully flexible device comprising polypyrrole as both electrodes and a PVDF membrane as separator, a capacitance of 30 F g^?1 was observed after 5000 cycles.     

Fuzzy nanofibrous network of polyaniline electrode for supercapacitor application

Fuzzy nanofibrous network of polyaniline electrode is successfully electrosynthesized for supercapacitor application. The nanofibre network of polyaniline electrode is characterized using Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM) and optical absorption studies. Network of polyaniline is highly porous with interconnected fuzzy nanofibres having diameter typically between 120 and 125 nm. The supercapacitive performance of polyaniline electrode is tested using cyclic voltammetry (C-V) technique in H₂SO₄ electrolyte within potential range of ?100 to 800 mV. The effect of scan rate on the capacitance of polyaniline electrode is studied. The highest specific capacitance of 839 F g^?1 at the voltage scan rate of 10 mV s^?1 is achieved. Additionally stability and charging–discharging of polyaniline electrode are studied.     

Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

Preparation and electrochemical properties of LiNi1/3Co1/3Mn1/3O2–PPy composites cathode materials for lithium-ion battery

Layered LiNi_1/3Co_1/3Mn_1/3O₂ was synthesized by co-precipitation method, and a series of polypyrrole–LiNi_1/3Co_1/3Mn_1/3O₂ composites were then prepared by polymerizing pyrrole monomers on the surface of LiNi_1/3Co_1/3Mn_1/3O₂. The bare sample and composites were subjected to analysis and characterization by the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical properties of the composites were investigated with galvanostatic charge–discharge test and AC impedance measurements, which show that the formed coats of polypyrrole (PPy) significantly decrease the charge-transfer resistance of LiNi_1/3Co_1/3Mn_1/3O₂. And the composite containing 2.0 wt% PPy exhibits a good electrochemical performance, its specific discharge capacity is 182 mAh g^?1 at 0.1C rate and voltage limits of 2.8–4.6 V, while the capacity of the bare sample is only 134 mAh g^?1.     

De-doped polyaniline nanofibres with micropores for high-rate aqueous electrochemical capacitor

Polyaniline nanofibres have been prepared without any template or surfactant. Although the morphology of polyaniline is well kept after dealing with aqueous ammonia, de-doped polyaniline nanofibres with micropores are of better electrochemical capacitor performances in 1 M H₂SO₄ aqueous solution. Its specific capacitance is 593 F g^?1 at a constant current density of 2.5 A g^?1, and can be subjected to charge/discharge over 5000 cycles in the voltage range of 0–0.65 V. Moreover, its capacitance retention ratio reaches circa 87% with the current densities increasing from 2.5 A g^?1 to 15 A g^?1.     

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO₃, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145 nm by increasing AgNO₃ concentration from 0.27 M to 1.08 M and that of PPy varies from 145 nm to 345 nm by changing pyrrole concentration from 1 × 10^?4 to 2 × 10^?4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag⁺ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2 S/cm, 7 orders higher than that of PPy nanorods (9.3 × 10^?4 S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO₃ initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.     

Pseudocapacitance properties of AC/LiNi1/3Co1/3Mn1/3O2 asymmetric supercapacitor in aqueous electrolyte

NH₂NH₂·H₂O which was used as controlling agent was applied to prepare the precursor Ni_1/3Co_1/3Mn_1/3(OH)₂ in the hydroxide co-precipitation method. The precursor was used to synthesize LiNi_1/3Co_1/3Mn_1/3O₂. The samples were characterized by XRD, XPS and SEM. It has been found that sintered sample at 800 °C for 16 h is considered as the optimal synthetic condition. The LiNi_1/3Co_1/3Mn_1/3O₂ was used as positive electrode and the activated carbon as negative electrode of the asymmetric supercapacitor. The electrochemical capacitance performance was tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge. The results indicate that species of aqueous electrolyte, current density, scan rate and potential limit, etc. have influence on the capacitance property of AC/LiNi_1/3Co_1/3Mn_1/3O₂ supercapacitor. The initial discharge specific capacitance of 298 F g^?1 was obtained in 1 mol L^?1 Li₂SO₄ solution within potential range 0–1.4 V at the current density of 100 mA g^?1 and was cut down less than 0.058 F g^?1 per cycling period in 1000 cycles. The asymmetric supercapacitor exhibited a good cycling performance.     

Investigation of polyaniline co-doped with Zn2+ and H+ as the electrode material for electrochemical supercapacitors

Polyaniline co-doped with Zn²⁺ and H⁺ was synthesized in aqueous HCl solution containing ZnCl₂, and tested for its supercapacitive behavior in three-electrode or two-electrode system with 1.0 M H₂SO₄ as electrolyte by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) techniques were employed for characterization of polyaniline co-doped with Zn²⁺ and H⁺. Compared with polyaniline doped with H⁺, it shows a larger specific capacitance of 369 F g^?1. Moreover, the specific capacitance remains 90% after 1000 cycles at a current density of 0.5 A g^?1, indicating good cycleability.     

RuOx/polypyrrole nanocomposite electrode for electrochemical capacitors

In this study, ruthenium oxide-polypyrrole (RuOx-PPy) composite nanostructures were prepared as electrode materials for electrochemical capacitors. Pyrrole was electrochemically polymerized in the pores of an anodized aluminum oxide (AAO) template. RuOx was further deposited on the surface of the PPy nanorod array by an electrochemical method. The morphology and composition of the RuOx-PPy nanocomposites were observed by SEM and EDX. The capacitive performance of the RuOx-PPy nanocomposites was investigated by the galvanostatic charge/discharge test as a function of the amount of RuOx. The maximum specific capacitance of the RuOx-PPy nanocomposite electrode was 419 mF cm^?2/681 F g^?1.     

Preparation and enhanced stability of flexible supercapacitor prepared from Nafion/polyaniline nanofiber

Polyaniline nanofibers were used to produce a flexible supercapacitor electrode with a specific capacitance of 235 F g^?1. Cycle life and energy density were enhanced after encapsulating the polyaniline nanofiber electrode in Nafion. A specific capacitance of 195 F g^?1 was obtained over 10,000 charge–discharge cycles.A fully flexible, stand alone capacitor comprising two polyaniline nanofiber based electrodes and a PVDF separator was constructed. An initial specific capacitance of 125 F g^?1 (100 mV s^?1) was obtained. This decreased to 95 F g^?1 over 10,000 cycles.     

Organic conductor: Influence of preparation temperature

The conducting polypyrrole–polyethylene glycol (PPy–PEG) composite films were produced at various polymerization temperature ranging from 5 °C to 60 °C using 1 × 10^?3 M PEG, 0.20 M pyrrole and 0.10 M p-toluene sulfonate at 1.20 V (vs. SCE). The polymerization temperature of 5 °C appeared as the optimum preparation temperature showing the highest electrical conductivity of 70 S/cm and the thermal diffusivity of 8.76 × 10^?7 m² s^?1. The electrical conductivity and thermal diffusivity exhibited a decreasing trend with the increase in polymerization temperature in the pyrrole solution used to prepare the composite films. The XRD results reveal that low temperature (5 °C) typically results in more crystalline films, which are denser, stronger and have higher conductivity. The optical microscopy of PPy–PEG shows the globular surface morphology. The surface of the of the solution side of PPy–PEG film prepared at low temperatures showed a globular morphology.     

Polypyrrole nanowire modified graphite (PPy/G) electrode used in capacitive deionization

With high specific capacitance and good conductivity, polypyrrole nanowire modified graphite (PPy/G) electrode has great promising applications in capacitive deionization (CDI). Preparation parameters of modified electrode such as concentration of supporting electrolyte solution (LiClO₄), concentration of monomer (pyrrole, Py), pH of polymerization medium, polymerization potential and time have significant effects on the electrode adsorption capacity of NaCl. The experimental results indicate that the optimal preparation condition of the PPy/G electrode used for CDI is 0.10 M LiClO₄, 0.19 M Py and pH 5.91 which was controlled by phosphates buffer solution (PBS, 0.10 M), polymerized at 0.85 V vs saturated calomel electrode (SCE) with polymerization time of 150 s. The obtained electrode has an area specific capacitance of 0.188 F/cm² determined by cyclic voltammetry (CV) method in 1.0 M HClO₄ at a scanning rate of 0.05 V/s. In addition, the desalination experiments of the electrode were carried out in 500 ppm NaCl solution at a working voltage of 1.4 V. The experimental results indicate that the NaCl can be removed from the feed solution by electroadsorbing of the electrode with good desalination stability and the electrode can be regenerated efficiently by its electrodesorbing.     

Influence of the scan rate on the morphology of polyaniline grown on conducting fabrics. Centipede-like morphology

We report the apparition of different polyaniline (PANI) morphologies when different scan rates were employed in the electrochemical deposition of PANI on conducting fabrics. The most impressive structure obtained was the centipede-like morphology. PANI was deposited on conducting textiles of polyester covered with polypyrrole (PPy)/anthraquinone sulphonic acid (AQSA) by means of cyclic voltammetry. With the scan rates of 50 mV s^?1 and 5 mV s^?1 PANI with centipede-like morphology was obtained in the first scans. Globular PANI gained importance for higher number of scans due to the formation of new nucleation sites. When a scan rate of 1 mV s^?1 was employed a variety of different morphologies were observed, such as: fibrillar, stalagmite-like, coral-like and plain irregular forms. Such variety of morphologies is due to the slow growth that allowed different types of morphologies.     

Reticulated vitreous carbon/polypyrrole composites as electrodes for lithium batteries: Preparation,electrochemical characterization and charge–discharge performance

Polypyrrole (PPy) composites were prepared via electrochemical deposition onto reticulated vitreous carbon (RVC) – a tridimensional material – and tested as cathodes in lithium batteries. Different RVC/polypyrrole electrodes were prepared and characterized: PPy doped with ClO₄^? (RVC/PPy) as an anion-exchanger film; PPy doped with a large anion – poly(styrenesulphonate) – (RVC/PPyPSS) as a cation-exchanger film; and a bi-layer polymeric film formed by an inner layer of the former and an outer layer of the latter (RVC/PPy/PPyPSS). Photomicrographies, voltammetric profiles and electrochemical impedance spectroscopy data have shown different morphological and electrochemical characteristics for polypyrrole doped with small or large anions, and a peculiar behavior for the bi-layer electrodes. Charge/discharge results indicated that the RVC/PPy electrode can attain specific capacities as high as 95 mAh g^?1. PSS-doped polypyrrole electrodes also presented high specific-capacity values when the bi-layer configuration (RVC/PPy/PPyPSS) and lower charge–discharge currents were used. Impedance data indicated that the counter-ion diffusion within the bi-layer is hindered, which explains the slower activation of this composite when compared to that of RVC/PPy.     

The preparation and properties of sodium and organomodified-montmorillonite/polypyrrole composites: A comparative study

Two montmorillonites, an inorganic sodium montmorillonite (NaMMT) and an organo-modified montmorillonite (OMMT), were used for the preparation of montmorillonite/polypyrrole (MMT/PPy) composites. MMT particles were modified by the in situ polymerization of pyrrole in water, in aqueous solution of dodecylbenzenesulfonic acid (DBSA) used as anionic surfactant, and in water/methanol. Ferric chloride was used as oxidant in each case. Wide angle X-ray scattering (WAXS) measurements proved the intercalation of PPy into the galleries of NaMMT regardless the reaction media. In contrast, for OMMT/PPy composites, the increase of interlayer spacing depends on the preparation conditions, the highest increase in interlayer spacing was achieved in water/DBSA solution. The WAXS patterns of OMMT/PPy composites synthesized in methanol/water showed no change in interlayer spacing and the electrical conductivity of these composites was low, similar to that of NaMMT/PPy composites prepared under the same conditions. Conductivity about 1.1 S cm⁻¹ was reached for OMMT/PPy composites containing 13.3 wt% PPy prepared in the presence of DBSA. The NaMMT/PPy composite containing 15.6 wt% PPy and prepared under the same conditions showed a conductivity of 0.26 S cm⁻¹. X-ray photoelectron spectroscopy (XPS) proved that the surface of NaMMT/PPy composites is rich in MMT, whereas more PPy was found on the surface of OMMT/PPy composites. The conductivity of composites correlated with the N/Si atomic ratio determined from XPS results, which was taken as a semi-quantitative measure of the PPy surface fraction.     

Synthesis and supercapacitive behavior of carbon aerogel microbeads encapsulated by in situ Co3O4 nanoparticle

Co₃O₄/carbon aerogel microbead (Co₃O₄/CAMB) composites are prepared by in situ coating method and their supercapacitive behaviors are investigated. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrum, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectrum are used to characterize the structure and morphology of Co₃O₄/CAMB. The results show that nano-sized Co₃O₄ particles are homogenously encapsulated on the surface of CAMB. Electrochemical performances of the composite electrodes with different Co₃O₄ amount are studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge measurements. It is found that Co₃O₄/CAMB composites show better electrochemical performance than CAMB, and the optimum content of Co₃O₄ in Co₃O₄/CAMB composites is 10 wt.%. The specific capacitance of 10%–Co₃O₄/CAMB composite in 6 mol L^?1 KOH electrolyte is about 350.18 F g^?1 at a current density of 1 A g^?1. Moreover, 10%–Co₃O₄/CAMB composite supercapacitor exhibits relatively good high-rate capability and excellent cycle life.     

Structure and properties of solid-state synthesized poly(3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene)

A polyterthiophene derivative: poly(3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene) was synthesized by solid-state oxidative-polymerization of 3′,4′-ethylenedioxy-2,2′:5′,2″-terthiophene (TET) in various ratios of oxidant (FeCl₃) to the monomer (TET). The resulting polymers were characterized by FT-IR, ¹H NMR, TEM, SEM, UV–vis–NIR, GPC, X-ray diffraction, EDX, CV, galvanostatic charge–discharge, as well as TGA and conductivity measurements. The results showed that the as-made poly(TET)s were partially in doped state with a conductivity ranging from 2.1 × 10^?3 S cm^?1 to 8.1 × 10^?3 S cm^?1 at room temperature, and exhibited good thermal stability in nitrogen up to 337–356 °C. The poly(TET)s showed a similar UV–vis absorption peak at 462 nm in acetonitrile. In addition, as-made poly(TET)s had low molecular weight ranging from 3300 to 3500 with microstructured morphology including nanorodes and nanofibers, and presented one redox couple at 1.1–1.2 V(ox) and 0.6–0.7 V(re) in 0.1 M Et₄NBF₄ acetonitrile solution. A moderate specific capacitance of 71 F g^?1 for poly(TET) modified graft electrode was obtained within the potential range of ?0.2 V to 0.5 V in 1 M H₂SO₄ solution. X-ray diffraction results imply the enhanced crystallinity of poly(TET)s, indicating the existence of crystalline phase in polymer matrix. Furthermore, the comparison of results from every measurement indicated that the [FeCl₃]/[TET] ratio strongly affects the morphology of the poly(TET), and the fibrillar growth tendency of poly(TET) was observed with the increase of the [FeCl₃]/[TET] ratio, and long-length fibrillar morphology occurred in the highest [FeCl₃]/[TET] ratio.     

Preparation and electrochemical performances of graphite oxide/polypyrrole composites

Graphite oxide/polypyrrole composites (GPys) were prepared by in situ polymerization and reduced by NaBH₄ to prepare reduced graphite oxide/polypyrrole composites (R-GPys). On the basis of the morphological and structural characterization of the composites by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests, the electrochemical performances of the composites were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance techniques. The experimental results showed that the specific capacitances of the composites before and after reduction (197 and 180 F/g) were highly improved compared with that of pristine graphite oxide (11 F/g) and polypyrrole (112 F/g), respectively. The capacitance retention of about 73% for R-GPys compared with 12% for PPy and 47% for GPys after 1200 cycles indicated the high cycle stability of the R-GPys and its potential as an electrode material for supercapacitor applications.