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.     

Facile synthesis and strongly microstructure-dependent electrochemical properties of graphene/manganese dioxide composites for supercapacitors

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO₂ composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO₂ composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO₂ composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO₂ composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO₂ composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles.

PACS

81.05.ue; 78.67.Sc; 88.80.fh     

Facile synthesis of reduced graphene oxide/CeO2 nanocomposites and their application in supercapacitors

The combination of the attractive properties of graphene with excellent characteristics of other functional nanomaterials has become a popular pathway for achieving applications in multiple fields. Herein, reduced graphene oxide (RGO)/CeO₂ nanocomposites with enhanced capacitive performance were designed and synthesized by a facile two-step approach with a self-assembly method followed by thermal treatment. The structure, morphology and composition of the resulting RGO/CeO₂ nanocomposites were systematically investigated. The presence of RGO can prevent the aggregation and control the structures of the CeO₂ nanocrystals in the annealing process. The nanocomposites as electrode materials for supercapacitor exhibited an enhanced capacitive performance due to the synergic effect between RGO nanosheets and CeO₂ nanocrystals. The excellent capacitive performance of the RGO/CeO₂ nanocomposites offer great promise for supercapacitor applications.     

Facile synthesis and morphology control of graphene oxide/polyaniline nanocomposites via in-situ polymerization process

This study reports the synthesis of graphene oxide (GO)/polyaniline (PANI) nanocomposites with controllable morphologies through in-situ polymerization of aniline monomers in the presence of GO sheets. Specific reaction parameters including solution acidity, aniline concentration, and reaction temperature are used to control the final shape of the composite product. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images are used to explore the morphology of the composite. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), FT–IR and UV–vis spectrophotometers are utilized to characterize the intermediates and the final products of the GO/PANI composites. Experiment results reveal that the polymerization operated in low acidity and low temperature conditions inclines to form GO/PANI nanotubes. On the other hand, the polymerization operated in high acidity inclines to form either nanospheres or aligned nanofiber arrays. These different morphologies are resulted from different polymerization routes and the formation mechanisms of these different shapes of nanocomposites are explored. Among the various nanocomposites, the GO/PANI nanospheres exhibit a highest electrochemical surface area. This study provides a facile and effective strategy to control the morphology of GO/PANI nanocomposites with characteristic electrochemical property.     

Facile in-situ preparation of polyaniline/graphene nanocomposites using methanesulfonic acid

Polyaniline (PANI)/graphene composites were prepared by the in-situ polymerization of aniline in a 1 M aqueous solution of methanesulfonic acid (MSA) containing graphene, which was prepared separately from graphite powders by simple sonication in MSA. Graphite powders spontaneously exfoliated to form graphene (GPM), which was then quenched with excess water, filtered, and dried to produce powders. The dried graphene powders produced were re-dispersed well in a 1 M MSA aqueous solution, in which the in-situ polymerization of aniline was performed. The resulting PANI/GPM composite had a conducting emeraldine salt (ES) form, and showed good electrical and thermal properties, compared to pure PANI prepared using a 1 M HCl solution. The PANI/GPM composite could be dissolved in a MSA solution and spin-coated in a conducting ES form of PANI. In contrast, the ES form produced from a HCl solution was insoluble in organic solvents and needed to be reduced to convert it to the emeraldine base form to produce a PANI solution. Therefore, the in-situ preparation of PANI/graphene composites using MSA provides a facile means of improving the thermal and electrical properties of PANI and its processability.     

Covalently-grafted polyaniline on graphene oxide sheets for high performance electrochemical supercapacitors

A simple route to achieve covalently-grafted polyaniline (PANI)/graphene oxide (GO) nanocomposites has been developed. The synthesized composites showed a uniform hierarchical morphology of the PANI thin film and short rod-like nanostructures that had densely grown on the GO sheets, in contrast to the nonuniform morphology of noncovalently-grafted PANI/GO. Compared to pure PANI and noncovalently-grafted PANI/GO composites, the covalently-grafted PANI/GO composites possessed a much larger specific surface area and pore volume, which increased the accessible surface area for the redox reaction and allowed faster ion diffusion. This unique hierarchical morphology maximized the synergistic effect between PANI and GO, resulting in excellent electrochemical performance (capacitance 442 F/g of PANI/GO (6:1) vs. 226 F/g of pure PANI) and improved cycling stability (83% @ 2000 cycles of PANI/GO (6:1) vs. 54.3% @ 1000 cycles of pure PANI). The enhanced electrochemical performance demonstrates the advantage of the PANI/GO composites prepared via this covalent grafting method.     

Facile synthesis of NiAl-layered double hydroxide/graphene hybrid with enhanced electrochemical properties for detection of dopamine

Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clays, have been investigated widely as promising electrochemical active materials. Due to the inherently weak conductivity, the electrochemical properties of LDHs were improved typically by utilization of either functional molecules intercalated between LDH interlayer galleries, or proteins confined between exfoliated LDH nanosheets. Here, we report a facile protocol to prepare NiAl-LDH/graphene (NiAl-LDH/G) nanocomposites using a conventional coprecipitation process under low-temperature conditions and subsequent reduction of the supporting graphene oxide. Electrochemical tests showed that the NiAl-LDH/G modified electrode exhibited highly enhanced electrochemical performance of dopamine electrooxidation in comparison with the pristine NiAl-LDH modified electrode. Results of high-resolution transmission electron microscopy and Raman spectra provide convincing information on the nanostructure and composition underlying the enhancement. Our results of the NiAl-LDH/G modified electrodes with the enhanced electrochemical performance may allow designing a variety of promising hybrid sensors via a simple and feasible approach.     

Chemical reduction-induced fabrication of graphene hybrid fibers for energy-dense wire-shaped supercapacitors

The emerging one-dimensional wire-shaped supercapacitors(SCs) with structural advantages of low mass/volume structural advantages hold great interests in wearable electronic engineering. Although graphene fiber(GF) has full of vigor and tremendous potentiality as promising linear electrode for wire-shaped SCs, simultaneously achieving its facile fabrication process and satisfactory electrochemical performance still remains challenging to date. Herein, two novel types of graphene hybrid fibers, n...     

Facile synthesis of TiO2/graphene composites for selective enrichment of phosphopeptides

TiO(2)/graphene composites were synthesized through a simple one-step hydrothermal reaction and successfully used to selectively capture phosphopeptides from peptide mixtures for matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis.     

Facile approach to prepare multi-walled carbon nanotubes/graphene nanoplatelets hybrid materials

A facile approach was developed to prepare multi-walled carbon nanotubes/graphene nanoplatelets hybrid materials through covalent bond formation. First, poly(acryloyl chloride) was grafted onto oxidized multi-walled carbon nanotubes through the reaction between the acyl chloride groups of poly and the hydroxyl groups of oxidized multi-walled carbon nanotubes. Second, the remaining acyl chloride groups of poly were allowed to react with the hydroxyl groups of hydroxylated graphene nanoplatelets. Scanning electron microscopy and transmission electron microscopy data showed that the multi-walled carbon nanotubes and graphene nanoplatelets were effectively connected with each other. And Fourier transform infrared spectroscopy data indicated the formation of covalent bonds between carbon nanotubes and graphene nanoplatelets. Conformational changes were monitored by Raman spectroscopy. This novel kind of carbon hybrid materials may have the potential application in a wide field, especially in increasing the toughness and strength of the matrix resin.     

聚苯胺/壳聚糖超级电容器电极复合材料的制备及表征

采用冷冻干燥后管式炉碳化制备壳聚糖电极材料,经KOH活化法活化后通过氧化还原聚合法制备聚苯胺(PANI)/壳聚糖电极材料,运用循环伏安、交流阻抗、充放电等测试聚苯胺/壳聚糖电极的电化学性能。结果表明,聚苯胺/壳聚糖电极材料表现出良好的电容性能和稳定的电化学性能,比电容129.6 F/g,循环充放电500次,比电容保持率90.8%。     

聚苯胺/壳聚糖超级电容器电极复合材料的制备及表征

采用冷冻干燥后管式炉碳化制备壳聚糖电极材料,经KOH活化法活化后通过氧化还原聚合法制备聚苯胺(PANI)/壳聚糖电极材料,运用循环伏安、交流阻抗、充放电等测试聚苯胺/壳聚糖电极的电化学性能。结果表明,聚苯胺/壳聚糖电极材料表现出良好的电容性能和稳定的电化学性能,比电容129.6 F/g,循环充放电500次,比电容保持率90.8%。     

Rapid microwave-assisted synthesis of graphene nanosheet/Co3O4 composite for supercapacitors

Graphene nanosheet (GNS)/Co₃O₄ composite has been rapidly synthesized by microwave-assisted method. Field emission scanning electron microscopy and transmission electron microscopy observation reveals the homogeneous distribution of Co₃O₄ nanoparticles (3-5 nm in size) on graphene sheets. Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 243.2 F g⁻¹ has been obtained at a scan rate of 10 mV s⁻¹ in 6 M KOH aqueous solution for GNS/Co₃O₄ composite. Furthermore, the composite exhibits excellent long cycle life along with ∼95.6% specific capacitance retained after 2000 cycle tests.     

Electrospun polyaniline nanofibers web electrodes for supercapacitors

Polyaniline nanofibers (PANI‐NFs) web are fabricated by electrospinning and used as electrode materials for supercapacitors. Field‐emission scanning electron microscope micrographs reveal nanofibers web were made up of high aspect ratio (>50) nanofibers of length ～30 μm and average diameter ～200 nm. Their electrochemical performance in aqueous (1M H₂SO₄ and Na₂SO₄) and organic (1M LiClO₄ in propylene carbonate) electrolytes is compared with PANI powder prepared by in situ chemical oxidative polymerization of aniline. The electrochemical properties of PANI‐NFs web and PANI powder are studied using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. PANI‐NFs web show higher specific capacitance (～267 F g^?1) than chemically synthesized PANI powder (～208 F g^?1) in 1M H₂SO₄. Further, PANI‐NFs web demonstrated very stable and superior performance than its counterpart due to interconnected fibrous morphology facilitating the faster Faradic reaction toward electrolyte and delivered specific capacitance ～230 F g^?1 at 1000th cycle. Capacitance retention of PANI‐NFs web (86%) is higher than that observed for PANI powder (48%) indicating the feasibility of electro spun PANI‐NFs web as superior electrode materials for supercapacitors. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ideal asymmetric supercapacitors consisting of polyaniline nanofibers and graphene nanosheets with proper complementary potential windows

Polyaniline (PANI) nanofibers are synthesized via a chemical method of rapid mixing for the application of asymmetric supercapacitors. The diameter and aspect ratio of PANI nanofibers is found to be controllable by varying the aniline/oxidant concentration ratio. The ideal capacitive responses of PANI nanofibers between 0.2 and 0.7 V (vs. Ag/AgCl) in concentrated acidic media are demonstrated by cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) analyses coupled with a schematic equivalent-circuit model. The morphologies and textures of nanofibers are examined by scanning electron microscopic (SEM), transmission electron microscopic (TEM) and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopic analyses. An aqueous asymmetric supercapacitor, consisting of a PANI nanofiber cathode and a graphene anode, with proper complementary potential windows is demonstrated in this work, which shows the device energy and power densities of 4.86 Wh kg⁻¹ and 8.75 kW kg⁻¹, respectively.     

石墨烯气凝胶的制备及其对水中油分的吸附特性

以改性Hummers法制备出的氧化石墨（GO）为原料,乙二胺（EDA）为交联剂,通过液相化学交联法制备出以石墨烯为主体的多孔网状气凝胶（EGA）。利用电子扫描电镜（SEM）、电子透射电镜（TEM）及选区电子衍射（SAED）对其进行表征。以水中柴油为研究对象,考察所制EGA样品对水中柴油的吸附脱除效果。结果表明,石墨烯气凝胶对柴油的吸附量在前5 min上升迅速,在30 min左右达到吸附平衡。吸附过程遵循准二级动力学模型,且吸附速率随温度的升高而增加,体系的表观活化能E_a=23.94 kJ·mol^-1。颗粒内扩散模型拟合结果表明,EGA对水中柴油的吸附分为表面孔道吸附、气凝胶内部孔道扩散以及石墨烯片层间小孔道扩散。石墨烯气凝胶对柴油的吸附等温线与Freundlich模型较为吻合。     

Easy synthesis of porous graphene nanosheets and their use in supercapacitors

We report the easy synthesis of porous graphene nanosheets (PGNs) using the etching of graphene sheets by MnO₂. An electrode made from PGNs exhibits a specific capacitance of 154 F g^?1 at 500 mV s^?1 in 6 M KOH compared to a value of 67 F g^?1 for graphene nanosheets, and a low capacitance loss of 12% after 5000 cycles. Interestingly, PGN electrode material shows an excellent rate capability due to its open layered and mesopore structures that facilitate the efficient access of electrolytes to the electrode material and shorten the ion diffusion pathway through the porous sheets. This approach offers the potential for cost-effective, environmentally friendly and large-scale production of PGNs.