Enhanced rate performance of polypyrrole-coated sulfur/MWCNT cathode material: a kinetic study by electrochemical impedance spectroscopy

Lithium-sulfur batteries have a poor cyclability and inferior rate capability due to the shuttle effect of lithium polysulfides. To solve these problems, a sulfur-coated MWCNT composite (S/MWCNT) was coated with conductive polypyrrole (PPy) to trap the polysulfides and facilitate charge and lithium ion transport. From the contact angle measurement, it is found that the PPy coating improves the wettability of the S/MWCNT composite. Compared with the bare S/MWCNT composite, the PPy-coated S/MWCNT composite cathode exhibited improved cycle stability and high-rate performance. A reversible discharge capacity of 671 mAh g^?1 was maintained after 50 cycles at 3 C for the PPy-coated composite. The effect of PPy coating on kinetic property was investigated by electrochemical impedance spectroscopy (EIS). The electrolyte resistance, surface film resistance, charge transfer resistance, lithium ion diffusion coefficient, and exchange current density were evaluated from the EIS measurements. The EIS results reveal that the PPy coating increases both Li ion diffusion into the cathode and exchange current density. The as-prepared PPy-coated S/MWCNT composite can be considered to be a promising candidate for high capacity and high-rate performance cathode material.     

Synthesis,characterization and electrochemical impedance spectroscopy of VOx-NTs/PPy composites

Composites consisting of vanadium oxide nanotubes (VOx-NTs) and polypyrrole (PPy) were synthesized by a two-steps method. VOx-NTs were firstly prepared by a combined sol–gel reaction and hydrothermal treatment procedure, in which V ₂O₅ powder and H₂O₂ were used as raw materials and hexadecylamine as a structure-directing template. Then VOx-NTs/PPy composites were fabricated by a cationic exchange reaction between hexadecylamine and polypyrrole. The structure and morphology of the samples were investigated by SEM, TEM, XRD and FTIR techniques. The results confirmed that the template molecules were successfully substituted by the conducting polymers PPy without destroying the previous tubular structure. Electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the electrochemical kinetics of the samples. The results indicated that VOx-NTs/PPy composites had a lower charge transfer resistance and a faster lithium-ion diffusion speed than those of VOx-NTs, and the enhanced electrochemical kinetics could be attributed to the excellent electronic conductivity of polypyrrole.     

Study of alternating current conduction mechanism in polypyrrole-magnesium ferrite hybrid nanocomposite through correlated barrier hopping model

In the present work, both polypyrrole (PPy) and optimized polypyrrole–magnesium ferrite (PPy-MgFe₂O₄) hybrid nanocomposite were synthesized separately by simple oxidative chemical polymerization method and then structurally characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The FTIR spectrum of the composite showed the presence of characteristic absorption bands of both PPy and MgFe₂O₄ in the composite confirming interfacial interaction of PPy with MgFe₂O₄. That this interaction is not affected by crystalline behaviour of predominant MgFe₂O₄ particles but that MgFe₂O₄ has embedded in PPy matrix was confirmed by XRD studies. Agglomerated granular spherical morphology of the composite was confirmed by SEM studies. Decrease in AC conductivity of the composite as compared to PPy due to the formation of interfacial heterojunction barrier between p-type PPy and n-type MgFe₂O₄ was confirmed experimentally and well supported theoretically by calculating binding energy, hopping distance and density of states at Fermi level of PPy and the composite as per CBH model.     

Preparation and Characterization of Montmorillonite/Polypyrrole Nanocomposites by In-Situ Chemical Polymerization

After prior ultrasonic treatment of montmorillorite (MMT), montmorillonite/polypyrrole (MMT/PPy) nanocomposites containing 10–80% PPy were prepared by in-situ chemical polymerization of pyrrole at 0°C in the presence of MMT in aqueous solution with FeCl₃ as oxidant and dopant. X-ray diffraction showed an increase in the interlayer spacing from 1.26 nm for MMT to 1.55 nm for MMT/PPy-10% and 1.96 nm for MMT/PPy-80%, signifying PPy was intercalated into the MMT galleries. Infrared spectra revealed the shifts of C-N stretching vibration and in-plane deformation bands, as well as the N-H vibration peaks of PPy, suggesting the presence of interfacial interactions between MMT and PPy. Scanning electron microscopy micrographs showed a flake-like morphology for the MMT/PPy nanocomposites and the obtained PPy retained this kind of morphology after removal of MMT from the composites by Hydrofluoric acid etching, while the pristine PPy prepared under the same condition exhibited globular particles. It was found for the first time that the conductivity of MMT/PPy with more than 50% PPy was higher than that of pristine PPy, i.e. 2.72 S/cm, 3.68 S/cm, and 4.81 S/cm for MMT/PPy containing 50%, 60%, and 80% PPy, while the pristine PPy conductivity was 2.71 S/cm. Thermal gravimetric analysis suggested that the introduction of MMT clay resulted in improvement of thermal stability for the obtained nanocomposites.     

Preparation and electrochemistry of one-dimensional nanostructured MnO2/PPy composite for electrochemical capacitor

One-dimensional nanostructured manganese dioxide/polypyrrole (MnO₂/PPy) composite was prepared by in situ chemical oxidation polymerization of pyrrole in the host of inorganic matrix of MnO₂, using complex of methyl orange (MO)/FeCl₃ as a reactive self-degraded soft-template. The morphology and structure of the composite were characterized by infrared spectroscopy (IR) X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the MnO₂/PPy composite consists of α-MnO₂ and PPy with nanotube-like structure. Electrochemical properties of the composite demonstrated the material showed good electrochemical reversibility after 500 charge-discharge cycles in the potential range of −0.4 to 0.6 V, the tube-like nanocomposite has the potential application in electrochemical capacitor.     

Synthesis and characterization of silver-polypyrrole film composite

In this work, we report the chemical polymerization of pyrrole to obtain thin film of polypyrrole (PPy) hydrochloride deposited onto the electrode of the quartz crystal microbalance (QCM). The film in the base form was exposed to a solution of AgNO₃. Electroless reduction for silver ions by the PPy film took place and silver particles were adsorbed onto the film surface. The silver particles content at the PPy films were analyzed by QCM and the results showed that the concentrations of silver uptakes increase as the original AgNO₃ solution increases. The morphology of the surface of the PPy film and the silver-PPy film composite were studied by the scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX). They showed that the obtained silver particles have spherical, cubic and tetrahedral structures. X-ray diffraction (XRD) and Fourier transformed infra-red spectroscopy (FTIR) were used to characterize the structure of the powder composite. This work reveals the capability of PPy film coating on QCM in sensing and removing silver from several environmental samples.     

Preparation of Si-PPy-Ag composites and their electrochemical performance as anode for lithium-ion batteries

The nanosilicon connected by polypyrrole (PPy) and silver (Ag) particles was simply synthesized by a chemical polymerization process in order to prepare Si-based anodes for Li-ion batteries. The phase structure, surface morphology, and electrochemical properties of the as-synthesized powders were analyzed by X-ray diffraction, FT-IR, scanning electron microscopy, and galvanostatic charge/discharge measurements. The cycle stability of the Si-PPy-Ag composites was greatly enhanced compared with the pure nanosilicon. A high capacity of more than 823 mA h g^?1 was maintained after 100 cycles. The improved electrochemical characteristics are attributed to the volume buffering effect as well as effective electronic conductivity of the polypyrrole and silver in the composite electrode.     

Polypyrrole nanocomposite made by polypyrrole dispersion in poly (vinyl alcohol) matrix

Polypyrrole-polyvinyl alcohol (PPy-PVA) nanocomposite is synthesized by dispersing interface polymerized polypyrrole in PVA matrix. The composite films are characterized by FTIR, XRD and SEM. FTIR spectra indicates crosslinking in the composite film. XRD pictures show more crystallinity for higher polymerization temperature, whereas SEM pictures clearly indicate PPy rod formation for the same film. The electrical conductivity of the films is in the range of 10⁻¹ S/cm, whereas the current-voltage (I–V) characteristics shows power law behaviour.     

Study of DC conductivity and relative magnetic permeability of nanoparticle NiZnFe2O4/PPy composites

The DC conductivity and the relative magnetic permeability have been measured as functions of temperature for five powder samples of nanoparticle ferrites (Ni_xZn_1−xFe₂O₄; x=0, 0.25, 0.5, 0.75 and 1), a pure polypyrrole (PPy) powder sample and many composite samples prepared by mixing different ratios of the ferrites to PPy. By comparing the results it is found that there is an obvious increase in DC conductivity of the ferrite/PPy composite samples compared to the corresponding pure ferrite samples, whereas compared to the pure PPy sample there is a decrease in DC conductivity. On the contrary, the magnetic permeability of the composites is higher than that of the pure PPy sample and lower than that of the pure ferrite samples as was expected.     

Novel Nanocomposites of Polypyrrole Doped with Fullerene C60

This paper reports on the structural, thermal, and dielectric properties of polypyrrole/fullerene C₆₀ nanocomposites synthesized by a interfacial polymerization method. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) analyses clearly indicated the existence of interactions between polypyrrole (PPy) and the fullerene C₆₀ nanoparticles. Thermal analyses indicated that the extrapolated onset degradation temperature (T_deg) of PPy increased with increasing doping level. Scanning electron microscopy (SEM) images showed that the fullerene C₆₀ changed the morphology of PPy. Dielectric analyses showed a temperature dependent dielectric relaxation behavior. The relaxation time of the nanocomposites with high doping levels tended to increase with increasing temperature. This behavior of the polypyrrole/fullerene C₆₀ nanocomposites indicated that they could be used as a high temperature ultrasonic transducer.     

Electrical conductivity of individual polypyrrole microtube

Conducting microtubes (0.4－0.5μm in outer diameter) made of polypyrrole (PPy) doped with p-toluene sulfonic acid (PTSA) were synthesized by a self-assembly method. We report the electrical conductivity of an individual PPy microtube, on which a pair of platinum micro-leads was fabricated by focused ion beam deposition. The measured room-temperature conductivity of the individual PPy microtube was 0.29S/cm, which is comparable to that of template-synthesized PPy micro/nanotubes. The temperature dependence of conductivity of the individual microtube follows the three-dimensional variable-range hopping (3D VRH) model.     

Combination of Fe-Mn based Li-rich cathode materials and conducting-polymer polypyrrole nanowires with high rate capability

The polypyrrole (PPy) nanowires are conducting 1D materials, which can significantly improve the electrical conductivity of the composites. A novel Li_1.26Fe_0.22Mn_0.52O₂ (LFMO) @ PPy nanowire composites were synthesized by simply ultrasonic dispersing LFMO and PPy nanowires in aqueous ethanol. The structure and morphology of pristine LFMO and LFMO@PPy are investigated by XRD, SEM, and TEM. The elemental mapping and FTIR results demonstrate the conductive network of PPy nanowires exists in the composites and the LFMO particles uniformly distribute on the PPy nanowires. LFMO combined with PPy nanowires exhibits better rate capability, higher capacity, coulombic efficiency, and cycleability than the pristine. The rate performance of composites with 10 wt% PPy nanowires shows the discharge capacities of 132.2 mAh/g and 98 mAh/g at 1C and 3C rate after 50 cycles, respectively. Electrochemical impedance spectroscopy test suggests that the conductive PPy nanowires can significantly decrease the charge-transfer resistance of LFMO. The composite with 10 wt% PPy nanowires shows a discharge capacity retention of 71% after 50 cycles at 1C, while the pristine sample only has 50% capacity retention.     

介孔二氧化硅基导电聚合物复合材料热导率的实验研究

本文首先制备并表征了介孔二氧化硅SBA-15、 填充导电聚合物的复合材料PANI/SBA-15和复合材料PPy/SBA-15, 并建立双流计实验台开展了材料压片情况下的热导率研究. 在测量得到复合材料热导率的基础上, 引入当量孔径, 结合测量孔径对 PANI/SBA-15和PPy/SBA-15复合材料热导率随填充量的变化进行了定性分析. 分析表明: PANI/SBA-15和PPy/SBA-15复合材料的热导率比基材SBA-15的热导率大得多; 在相同的测量孔径和当量孔径情况下, PANI/SBA-15复合材料的热导率比PPy/SBA-15复合材料的热导率大; 导电聚合物填充到复合材料孔道内和孔道外都有助于热导率的提高, 填充到孔道内比填充到孔道外对热导率提高的贡献更大.     

Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Thermal and Spectral Dielectric Properties of Polypyrrole/Polymethylmethacrylate Composites

Thermal properties of polypyrrole/polymethylmethacrylate (PPy/PMMA) composites were analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). A decrease in the glass transition temperatures with PPy concentration reveals the increase of segmental motion. The dielectric properties of these composites were studied for several weight concentrations of PPy in the frequency range between 500 Hz and 0.2 MHz, over the temperature range 23–110°C. Jonscher's phenomenological model has been used for modeling the dielectric response of the composite materials. This study shows that the results obtained for the dielectric response are in good agreement with the results of TGA and DSC measurements.     

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g^?1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.     

Morphological effects of single-layer graphene oxide in the formation of covalently bonded polypyrrole composites using intermediate diisocyanate chemistry

Single-layer graphene oxide (SLGO) possesses carboxylic and hydroxyl groups suitable for reactions with aliphatic or aromatic diisocyanate molecules. TEM analysis reveals that aliphatic diisocyanate molecules caused SLGO to scroll into star-like formations, whereas aromatic diisocyanate molecules retained SGLO in a flat-sheet morphology. TGA confirms the stabilisation of the formed urea and urethane groups on SLGO, but the onset of sheet pyrolysis occurs at a lower temperature due to isocyanate reactions with anhydride and epoxide groups embedded in the sheet. Pendant isocyanate groups act as bridging units to facilitate the attachment of pyrrole molecules, which are then used as anchor sites for the covalent polymerisation of pyrrole to polypyrrole (PPy). The use of FeCl₃ as the polymerisation catalyst generated both covalent and free PPy, but also iron hydroxide nanoparticles were observed decorating the SLGO surface. When using ammonium persulfate as a catalyst and dodecylbenzenesulfonate as a dopant, free PPy could be removed under treatment with solvents to leave a purely covalent system. Discrete regions of SLGO were observed decorated with nanoparticles of PPy along the edge or across the surface of individual sheets. It was found that the flexibility of the SLGO sheet and the type of diisocyanate used directly affected the electrical resistance of the final composite.     

PPy/Nafion复合膜的制备及性能表征

用0.5mol.L-1的FeCl3溶液作引发剂,采用原位化学聚合法将吡咯单体聚合在Nafion117膜基体中。复合膜的红外光谱图中出现明显聚吡咯（PPy）的特征吸收峰,说明吡咯单体聚合在Nafion117膜中。机械性能测试表明复合膜的拉伸强度比Nafion117膜提高了。热重测试表明复合膜具有更高的热稳定性能。对复合膜进行了甲醇渗透性能的测试,结果表明复合膜具有明显的阻醇作用,PPy/NF-3膜的甲醇渗透率值是5.9×10^-7cm^2.s^-1,和Nafion117膜相比降低了53%。     

Synthesis of RGO/Cu8S5/PPy Composite Nanosheets with Enhanced Peroxidase‐Like Activity for Sensitive Colorimetric Detection of H2O2 and Phenol

In this paper, a novel strategy for the fabrication of reduced graphene oxide (rGO)/Cu₈S₅/polypyrrole (PPy) composite nanosheets with Cu₈S₅ nanoparticles and PPy layer anchored on the surface of rGO as peroxidase‐like nanocatalyst is reported. During the synthesis, graphene oxide (GO)/CuO composite nanosheets are prepared first and used as templates, then the sulfuration of CuO and polymerization of pyrrole are accompanied with the reduction of GO, resulting in ternary rGO/Cu₈S₅/PPy composite nanosheets. The synthesized Cu₈S₅ nanoparticles with a diameter in the range from tens to hundreds of nanometers are dispersed within PPy decorated rGO nanosheets. The resultant ternary rGO/Cu₈S₅/PPy composite nanosheets exhibit a higher peroxidase‐like catalytic activity toward the oxidation of 3,3′,5,5′‐tetramethylbenzidine in the presence of H₂O₂ than GO/CuO and rGO/CuS composite nanosheets, revealing a synergistic effect on their activity. The as‐prepared rGO/Cu₈S₅/PPy platform provides a simple colorimetric approach for the detection of H₂O₂ and phenol with a high sensitivity. This work offers a new way for the fabrication of rGO‐based nanocomposite with superior enzyme‐like activity, which displays great potential applications in biocatalysis and environmental monitoring.     

Preparation and photovoltaic property of a new hybrid nanocrystalline SnO2/Polypyrrole p–n heterojunction

Hybrid photovoltaic structures based on transparent conductive SnO₂ and electrically conductive polypyrrole (PPy) were prepared. Nanocrystalline SnO₂ is considered an n-type barrier and window layer on p-type PPy layer in cell structures. The surface morphology and thickness of the layers were studied using scanning electron microscopy. The optical absorbance data showed an increase of absorbance in contrast with PPy and SnO₂. There was a red shift in absorbance wavelengths and a decrease in band gaps for the prepared PV structures. To investigate the electrical properties of the obtained structures, current-voltage characteristic was measured. The best structure showed an open-circuit voltage of 0.170?V, a short-circuit current density of 0.017?mA/cm², a fill factor of 0.36 and power conversion efficiency of 0.076.