Preparation and electrochemistry of nanostructured PPy/graphite nanosheets/rare earth ions composites for supercapacitor

Highly conductive PPy/graphite nanosheets/rare earth ions (PPy/nanoG/RE³⁺) composites were prepared via in‐situ polymerization with p‐toluenesulfonic acid as a dopant and FeCl₃ as an oxidant. The microstructures of nanoG and PPy/nanoG/RE³⁺ were characterized by the SEM and TEM examinations. It was found that nanoG and PPy nanospheres formed the uniform composite with the PPy nanospheres embedded on the nanoG surface and/or filled between the nanoG. The effects of nanoG and RE³⁺ on the electrical conductivity and electrochemical performance of the composites were investigated. The results showed that the nanoG and RE³⁺ as the filler had effect on the conductivity and electrochemical performance of PPy/nanoG/RE³⁺ composites, which played an important role in forming a conducting network in PPy matrix. A specific capacitance of as high as 175 F/g at a current density of 1 A/g was achieved over the PPy/nanoG/Gd³⁺ composite. The capacitance of the PPy/nanoG/Gd³⁺ composite decreased only 5.1% after 800 charging/discharging cycles at a current density of 1 A/g. POLYM. ENG. SCI., 54:2731–2738, 2014. © 2013 Society of Plastics Engineers     

One‐step synthesis of highly conductive PPy/graphite nanosheets/Gd3+ composites

Highly conductive polypyrrole/graphite nanosheets/Gd³⁺ (PPy/nanoG/Gd³⁺) composites are fabricated via in situ polymerization using p‐toluenesulfonic acid as a dopant and FeCl₃ as an oxidant. The effects of the graphite nanosheets and Gd³⁺ loading on the electrical conductivity are investigated. The maximum conductivity of PPy/nanoG/Gd³⁺ composites about 17.86 S/cm found with 3 wt% graphite nanosheets and 6 wt% Gd³⁺ at room temperature. The results showed that the high‐aspect‐ratio structure of graphite nanosheets played an important role in forming a conducting network in PPy matrix. Thermal gravimetric analysis demonstrates an improved thermal stability of PPy in the PPy/nanoG/Gd³⁺ composites. The microstructures of PPy/nanoG/Gd³⁺ are evidenced by the SEM and TEM examinations. POLYM. COMPOS., © 2011 Society of Plastics Engineers.     

Synthesis and properties of conducting polypyrrole,polyalkylanilines, and composites of polypyrrole and poly(2‐ethylaniline)

Conducting polymers of alkylanilines, pyrrole, and their conducting composites were synthesized by oxidation polymerization. The oxidants used were KIO₃ and FeCl₃ for the polyalkylanilines and polypyrrole (PPy), respectively. Among the polyalkylanilines synthesized with KIO₃ salt, the highest conductivity was obtained with poly(2‐ethylaniline) (P2EAn) with a value of 4.10 × 10^?5 S/cm. The highest yield was obtained with poly(N‐methylaniline) with a value of 87%. We prepared the conducting composites (PPy/P2EAn and P2EAn/PPy) by changing synthesis order of P2EAn and PPy. The electrically conducting polymers were characterized by IR spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, and X‐ray diffraction spectroscopy. From the results, we determined that the properties of the composites were dependent on the synthesis order of the polymers. The thermal degradation temperature of PPy was observed to be higher than that of the other polymers and composites. We determined from X‐ray results that the structures of the homopolymers and composites had amorphous regions (88–95%) and crystal regions (5–12%). From the Gouy balance magnetic measurements, we found that the polymers and composites were bipolaron conducting mechanisms. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 241–249, 2006     

Electrical resistivity of silicon nitride-silicon carbide based ternary composites

New electrically conductive ternary composites were developed by adding 8 vol.% of ZrN or ZrB₂ to a Si₃N₄-SiC matrix. During hot pressing, ZrB₂ reacted with Si₃N₄ to form ZrSi₂, ZrN, Si and BN whereas added ZrN did not undergo any reactions in the Si₃N₄-SiC-ZrN composite. The composites modified by ZrN or ZrB₂ addition showed a lower resistivity (7 × 10³ Ω cm and 3 × 10⁻¹ Ω cm) compared to the matrix (3 × 10⁴ Ω cm). Further studies on the grain size distribution and the volume ratio of conducting and non-conducting phases excluded a percolation network of ZrN and ZrSi₂ grains. In fact, doping of SiC grains and modified grain boundaries as a consequence of the formation of liquid phases during sintering are suggested to be the reason for the significantly lower resistivity of materials containing ZrSi₂.A decrease in the composite resistivity due to a subsequent heat treatment was obtained for all hot-pressed composites.     

Nano-composite of polypyrrole/modified mesoporous carbon for electrochemical capacitor application

Nano-thin polypyrrole (PPy) layers were coated on chemically modified ordered mesoporous carbon (m-CMK-3) by an in situ chemical polymerization. Structural and morphological characterizations of m-CMK-3/PPy composites were carried out using field emission scanning electron microscopy. Pseudo-capacitive behavior of the deposited PPy layers on m-CMK-3 was investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. As results of this study, the thin layer of PPy in the composite electrode was effective to obtain fully reversible and very fast Faradaic reaction. A maximum discharge capacity of 427 F g⁻¹ or 487 F g⁻¹ after correcting for weight percent of PPy phase at the current density of 5 mA cm⁻², could be achieved in a half-cell setup configuration for the m-CMK-3/PPy composites electrode, suggesting its potential application in electrode material for electrochemical capacitors.     

Structural,mechanical, and electrical properties of electropolymerized polypyrrole composite films

Electrochemical polymerization of pyrrole in a solution containing dissolved poly(vinyl alcohol) (PVA) produces a homogeneous, free‐standing, flexible, and conductive polymer film. The films were characterized using infrared spectroscopy, wide‐angle X‐ray diffraction analysis, and scanning electron microscopy. The appearance of standard and some new absorption bands for polypyrrole (PPy) and PVA confirms the composite formation. The mechanical properties of conducting PVA + PPy films were studied and found to be improved with respect to the control PPy films. The electrical conductivity of the PVA + PPy films was measured by using standard four‐ and two‐probe methods. The conductivity of the films was found to depend on the pyrrole content. These conducting composites were further used as gas sensors by observing the change in current with respect to ammonia gas. It was observed that the current decreases when these composites were exposed to ammonia gas. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2511–2517, 2001     

Supercritical carbon dioxide processing of conducting composites of polypyrrole and porous crosslinked polystyrene

Conducting composites (∼3 mm in thickness) of polypyrrole (PPy) and porous crosslinked polystyrene (PCPS) were prepared by first impregnating PCPS with iodine (I₂), and then contacting it with pyrrole (Py). Both these steps were carried out with and without supercritical carbon dioxide. The use of supercritical CO₂ as a solvent for I₂ and Py facilitated the transport and deposition of these substances in the pores of the permanently porous host and produced composites with conductivities as high as 10⁻³ S cm⁻¹. Moreover, the deposition of I₂ in the pores could be controlled via the CO₂ pressure. The bulk and surface conductivities of the composite exhibited percolation behavior with respect to the amount of the I₂ deposited, whereas the volume conductivity exhibited a stepwise transition at approximately 100 wt% PPy+I₂ complex formed (with respect to the original mass of PCPS). Optical micrographs suggest that non-uniform distributions of PPy are obtained in the pores below this transition.The percolation threshold was as low as 10 wt% so that the stability and mechanical strength of the composites were approximately the same as those of the host PCPS. This was verified by TGA and compressive strength measurements. The temperature dependence of the conductivity conformed with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport. However, the data could be correlated equally well with the CELT model.     

Polypyrrole and La1−xSrxMnO3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium

Composite G/PPy/PPy(La_1−xSr_xMnO₃)/PPy electrodes made of the perovskite La_1−xSr_xMnO₃ embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La_1−xSr_xMnO₃) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm⁻³ pyrrole (Py) plus 0.05 mol dm⁻³ K₂SO₄ with and without containing a suspension of 8.33 g L⁻¹ oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm⁻³ K₂SO₄ plus 5 mmol dm⁻³ KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.     

Electrically conductive composites of polyurethane derived from castor oil with polypyrrole‐coated peach palm fibers

Electrically conducting fibers were prepared through in situ oxidative polymerization of pyrrole (Py) in the presence of peach palm fibers (PPF) using iron (III) chloride hexahydrate (FeCl₃·6H₂O) as oxidant. The polypyrrole (PPy) coated PPF displayed a PPy layer on the fibers surface, which was responsible for an electrical conductivity of (2.2 ± 0.3) × 10⁻¹ S cm⁻¹, similar to the neat PPy. Electrically conductive composites were prepared by dispersing various amounts of PPy‐coated PPF in a polyurethane matrix derived from castor oil. The polyurethane/PPy‐coated PPF composites (PU/PPF–PPy) exhibited an electrical conductivity higher than PU/PPy blends with similar filler content. This behavior is attributed to the higher aspect ratio of PPF–PPy when compared with PPy particles, inducing a denser conductive network formation in the PU matrix. Electromagnetic interference shielding effectiveness (EMI SE) value in the X‐band (8.2–12.4 GHz) found for PU/PPF–PPy composites containing 25 wt% of PPF–PPy were in the range −12 dB, which corresponds to 93.2% of attenuation, indicating that these composites are promising candidates for EMI shielding applications. POLYM. COMPOS., 38:2146–2155, 2017. © 2015 Society of Plastics Engineers     

Preparation, structure and electrochemistry of a polypyrrole hybrid film with [Pd(dmit)2], bis(1,3-dithiole-2-thione-4,5-dithiolate)palladate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Pd(dmit)₂] (1,3-dithiole-2-thione-4,5-dithiolate, [dmit]²⁻, [C₃S₅]²⁻) in acetonitrile solution is reported. FTIR and UV-vis spectroscopy showed that the [Pd(dmit)₂]²⁻ anion had been inserted in the polypyrrole framework without modification during the electropolymerization process. Cyclic voltammetry showed that the material has electroactivity undergoing redox processes related to the conducting polymer and the counteranion. The electrochemical results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Pd(dmit)₂]²⁻ exhibits good thermal stability and has a higher intrinsic conductivity value (4.27 × 10⁻³ S cm⁻¹) than do other PPy/dmit films previously studied.     

Synthesis of highly conductive PPy/graphene nanosheets/NiO composite using ultrasonic technique

Highly conductive polypyrrole/graphene nanosheets/NiO (PPy/GNS/NiO) composites are fabricated via ultrasound technique using p‐toluenesulfonic acid as a dopant and FeCl₃ as an oxidant. The effects of the GNS and NiO loading on the electrical conductivity are investigated. The maximum conductivity of PPy/GNS/NiO composites about 24.39 S/cm found with 3 wt% GNS and 48.7 wt% NiO at room temperature. The results showed that the high‐aspect‐ratio structure of GNS played an important role in forming a conducting network in PPy matrix. The microstructures of PPy/GNS/NiO are evidenced by the scanning electron microscope and transmission electron microscope examinations. The cyclic voltammetry curves can be seen that the PPy/GNS/NiO composites also have good electrochemical performance, and it can be used as a supercapacitor electrode material. POLYM. COMPOS., 34:997–1002, 2013. © 2013 Society of Plastics Engineers     

Polypyrrole/carbon composite electrode for high-power electrochemical capacitors

Nano-thin polypyrrole (PPy) layers with thickness from ∼5 nm to several 10s nm were deposited on vapor grown carbon fibers (VGCF) by an in situ chemical polymerization. Using different concentrations of the pyrrole could control the thicknesses of deposited PPy layers. Surface morphology and thickness of the deposited PPy layers were confirmed by means of scanning electron microscopy and scanning transmission emission microscopy. Pseudo-capacitive behavior of the deposited PPy layers on VGCF investigated by means of cyclic voltammetry. Then, the PPy/VGCF composites were mixed with activated carbons (AC) at various mixing ratios. For the PPy/VGCF/AC composite electrodes, characteristics of specific capacitance and power capability were examined by half-cell tests. As results of this study, it was investigated that nano-thin PPy layer below ∼10 nm deposited on VGCF had high pseudo-capacitance and fast reversibility. Its specific capacitance per averaged weight of active material (PPy) was obtained as ∼588 F g⁻¹ at 30 mV s⁻¹ and maintained as ∼550 F g⁻¹ at 200 mV s⁻¹ of scan rate. Also, from the mixing 60 wt.% of the PPy/VGCF with 25 wt.% of AC, the PPy/VGCF/AC composite electrode exhibited higher power capability maintaining the specific capacitance per active materials of PPy and AC as ∼300 F g⁻¹ at 200 mV s⁻¹ in 6 M KOH.     

Novel electrically conductive α-β SiAlON/TiCN composites

Electrically conductive α-β SiAlON/TiCN composites were produced in the form of a segregated network in a ceramic matrix structure. A continuous 3D network of conductive TiCN particles was successfully achieved by mechanically coating spray-dried SiAlON granules with varying amounts of nano sized TiCN (0-10 vol.%) particles. For comparison, the same SiAlON matrix was incorporated with 25 vol.% micron sized TiCN particles to give a particle reinforced composite. Densification, together with mechanical and electrical properties of the composites produced were discussed in terms of conventional and novel approach. Fully dense composites were obtained by gas pressure sintering (GPS) under a nitrogen pressure of 100 bar at a peak temperature of 1990 °C. The electrical resistivity of the SiAlON (1 × 10¹³ Ω m) matrix material was drastically reduced with the addition of only 5 vol.% TiCN (18 × 10⁻⁴ Ω m) to the composites prepared by the coating method.     

Transport properties in polypyrrole powders and in PPy–PVA composites: Evidence for bipolaronic clusters

Experimental results on electrical conductivity of both doped polypyrrole (PPy) powder and conducting poly(vinyl alcohol) (PVA)–PPy composite are presented. In each case, FeCl₃ has been used as the oxidizing–polymerizing agent. Results are interpreted on the basis of a model in which counter-ions act through their attractive potential by forming conducting ways between chains and allowing transverse conduction. In the case of PPy powder, the major contribution to conduction mechanisms is hopping between polaronic clusters. In the case of the composite, an additional contribution results from fluctuation-induced tunneling through thin insulating PVA barriers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:709–713, 1998     

Glucose oxidase electrodes based on microstructured polypyrrole films

Highly sensitive glucose oxidase (GOD) electrodes were fabricated on the basis of microstructured polypyrrole (PPy) films. The microstructures of the PPy films had a morphology like cups and were arranged in a density of approximately 4000 units/cm². GOD was immobilized in microstructured PPy films coated on a Pt or stainless steel (SS; AISI 321) substrate electrode. The GOD/PPy/Pt electrode showed a linear response to glucose concentrations in the range of 0–17 mM at a potential of 0.4 V (vs a saturated calomel electrode). Its sensitivity was measured to be approximately 660 nA/(mM cm²) at 15°C, and the response time (t_95%) was approximately 20 s. In comparison, the sensitivity of the GOD/PPy/Pt electrode based on a flat PPy film was only approximately 330 nA/(mM cm²) under the same conditions. The sensitivity of the microstructured GOD/PPy/Pt electrode could be increased to as high as approximately 2400 nA/(mM cm²) at 37°C. The microstructured GOD/PPy/SS electrode had a sensitivity of approximately 550 nA/(mM cm²) and a t_95% value of approximately 30 s at 15°C and 0.4 V. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2550–2554, 2005     

Hydrated Mn(IV) oxide-exfoliated graphite composites for electrochemical capacitor

Commercially available low cost exfoliated graphite (EG, nominal diameter 130 μm) was used as a conductive substrate for electrochemical capacitor of hydrated Mn(IV) oxide, MnO₂·nH₂O. The MnO₂·nH₂O-EG composites were prepared by addition of EG to potassium permanganate solution, followed by 1 h stirring and then slow addition of manganese(II) acetate solution. By this procedure submicrometer or smaller sized MnO₂·nH₂O particles having mesopores of 6-12 nm in diameter were formed on the graphite sheets of EG. Although EG alone showed only about 2 F g⁻¹, the composites showed good rectangular cyclic voltammograms at 2-20 mV s⁻¹ in 1 mol L⁻¹ Na₂SO₄. The capacitance per net amount of MnO₂ increased proportionally with EG content, that is, utilization ratio of MnO₂ increased with EG content. The composites of MnO₂·nH₂O and smaller diameter of EG (nominal diameter 45 μm) or artificial graphite powder (average diameter 3.7 μm) showed fairly good performance at 2 mV s⁻¹, but with increasing potential scan rate the rectangular shape was distorted and capacitance decreased drastically. The results implies that sheet-like structure is more effective than small particles as conductive materials, when the formation procedure of composite is the same. Large sized EG may be a promising conductive material for electrochemical capacitors.     

Preparation and characterization of new anhydrous, conducting membranes based on composites of ionic liquid trifluoroacetic propylamine and polymers of sulfonated poly (ether ether) ketone or polyvinylidenefluoride

A novel ionic liquid of trifluoroacetic propylamine, i.e., [CH₃CH₂CH₂NH₃⁺] [CF₃COO⁻] (TFAPA), was synthesized from trifluoroacetic acid and propylamine. The ionic liquid of TFAPA was used to prepare anhydrous, conducting membranes based on polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF). The ionic conductivity and mechanical strength of the composite membranes were investigated at elevated temperatures and under anhydrous conditions. Conductivity of 0.030 S/cm was achieved with TFAPA at 180 °C, and of 0.019 S/cm with a membrane containing 70% (wt) TFAPA in SPEEK with a sulfonation degree of 86% at 160 °C. Increasing either ionic liquid content or temperature reduced the mechanical strength of the composite membrane. Efforts were made to improve the strength of TFAPA/SPEEK composite membranes by cross-linking the SPEEK, which led to some strength enhancement at 110 °C and 130 °C.     

Manufacturing 2D carbon-fiber-reinforced SiC matrix composites by slurry infiltration and PIP process

Sub-micrometer SiC particles were firstly added to the preceramic solution in the first infiltration step to enhance the mechanical properties of 2D C_f/SiC composites fabricated via polymer infiltration and pyrolysis (PIP) process. The effects of pyrolysis temperature and SiC-filler content on microstructures and properties of the composites were systematically studied. The results show that the failure stress and fracture toughness increased with the increase of pyrolysis temperature. SiC filler of sub-micron scale infiltrated into the composites increased the mechanical properties. As a result, for the finally fabricated composite infiltrated with a slurry containing 40 wt.% SiC filler, the failure stress was doubled compared to that without SiC filler addition, and the fracture toughness reached ≈10 MPa m^1/2.     

Cellular structures of carbon nanotubes in a polymer matrix improve properties relative to composites with dispersed nanotubes

A new processing method has been developed to combine a polymer and single wall carbon nanotubes (SWCNTs) to form electrically conductive composites with desirable rheological and mechanical properties. The process involves coating polystyrene (PS) pellets with SWCNTs and then hot pressing to make a contiguous, cellular SWCNT structure. By this method, the electrical percolation threshold decreases and the electrical conductivity increases significantly as compared to composites with well-dispersed SWCNTs. For example, a SWCNT/PS composite with 0.5 wt% nanotubes made by this coated particle process (CPP) has an electrical conductivity of ∼3 × 10⁻⁴ S/cm, while a well-dispersed composite made by a coagulation method with the same SWCNT amount has an electrical conductivity of only ∼10⁻⁸ S/cm. The rheological properties of the composite with a macroscopic cellular SWCNT structure are comparable to PS, while the well-dispersed composite exhibits a solid-like behavior, indicating that the composites made by this new CPP are more processable. In addition, the mechanical properties of the CPP-made composite decrease only slightly, as compared with PS. Relative to the common approach of seeking better dispersion, this new fabrication method provides an important alternative means to higher electrical conductivity in SWCNT/polymer composites. Our straightforward particle coating and pressing method avoids organic solvents and is suitable for large-scale, inexpensive processing using a wide variety of polymers and nanoparticles.     

Novel Ni/polypyrrole and Cu/polypyrrole composites prepared in the presence of different acids: Synthesis and investigation of thermal stability

We report the synthesis and characterization of new organic/inorganic hybrid materials constituted of Ni(0) and Cu(0) nanoparticles and polypyrrole (PPy). Copper and nickel nanoclusters were synthesized by a chemical reduction of aqueous metal salt solutions by sodium borohydride. PPy/Ni(0) and PPy/Cu(0) composites were obtained in the presence of two different acids (H₃BO₃, CH₃COOH), by polymerizing pyrrole‐Ni and pyrrole‐Cu particles by using iron (III) chloride. The composites have been characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and magnetic susceptibility techniques. Conductivity measurements of samples were taken using four‐probe devices. The PPy/Ni(0) and PPy/Cu(0) nanocomposites doped with different acids exhibited higher conductivity values than those of homopolymers. Among all samples, Ni/PPy‐H₃BO₃ has the highest conductivity (1.42 S cm^?1). Homopolymers and composites showed a stable and increasing conductivity with increasing temperature, except Ni(0). We observed that from TGA analysis of polymers, metal composites of PPy synthesized in two different media are more stable than those of PPy‐CH₃COOH and PPy‐H₃BO₃. The magnetic susceptibility values of homopolymers and Cu are negative, whereas the other samples are positive. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007