Fabrication and electrochemical capacitance of hierarchical graphene/polyaniline/carbon nanotube ternary composite film

A film composed of graphene (GN) sheets, polyaniline (PANI) and carbon nanotubes (CNTs) has been fabricated by reducing a graphite oxide (GO)/PANI/CNT precursor prepared by flow-directed assembly from a complex dispersion of GO and PANI/CNT, followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. Scanning electron microscope images indicate that the ternary composite film is a layered structure with coaxial PANI/CNT nanocables uniformly sandwiched between the GN sheets. Such novel hierarchical structure with high electrical conductivity perfectly facilitates contact between electrolyte ions and PANI for faradaic energy storage and efficiently utilizes the double-layer capacitance at the electrode–electrolyte interfaces. The specific capacitance of the GN/PANI/CNT estimated by galvanostatic charge/discharge measurement is 569 F g⁻¹ (or 188 F cm⁻³ for volumetric capacitance) at a current density of 0.1 A g⁻¹. In addition, the GN/PANI/CNT exhibits good rate capability (60% capacity retention at 10 A g⁻¹) and superior cycling stability (4% fade after 5000 continuous charge/discharge cycles).     

Fabrication of highly conducting and transparent graphene films

Graphene-based transparent conducting films were prepared using the following method. A chemically-reduced graphene dispersion was synthesized and graphene films were prepared from it by transfer printing, followed by thermal treatment. The resulting graphene films possessed an excellent electrical conductivity with a high transparency. A sheet resistance lower than ∼2 KΩ/sq and a transparency well over 80% were achieved at a typical wavelength of 550 nm. These properties are considered quite sufficient for many applications, such as transparent conductor films for touch panels.     

Fabrication of graphene films with high transparent conducting characteristics

We present a study on the transparent conducting characteristics of graphene-based films prepared by means of rapid chemical vapor deposition. The graphene films were grown on quartz slides with a CH₄/Ar mixed gas under a constant flow at 950°C and then annealed at 1,000°C. It was found that the graphene films present excellent electrical conductivity with high transparency. The conductivity is up to 1,240 S/cm, the sheet resistance is lower than 1 kΩ/sq, and the transparency is well over 85% in the visible wavelength range of 400 to 800 nm, showing that the graphene films have very low resistivity and superior transparency and completely satisfy the need for transparent conductors. These properties can be used in many applications, such as transparent conductor films for touch panels.

PACS

61.48.+c, 78.67.Pt, 68.37.Hk, 68.65.Ac     

石墨烯复合负极材料的制备及电化学性能研究

介绍了石墨烯电极材料的储锂行为,分别综述了硅基、锡基、过渡金属氧化物、硫化物与石墨烯形成的复合负极材料的制备及性能改善的最近进展。将石墨烯与这些活性材料复合,可以有效地改善锂离子电池的循环稳定性和倍率性能。最后指出了石墨烯复合电极材料发展过程中存在的问题并对其前景进行了展望。     

Mechanical properties of free-standing graphene oxide

The mechanical properties of free-standing graphene oxide (GO) films were investigated using nanoindentation on a dynamic contact module (DCM) system. The Young's modulus, stiffness, and ultimate strength of thin films were evaluated. Nanoindentation measurements were combined with the DCM to evaluate the mechanical properties of thin films and to predict the crack length and critical energy. Electrophoretically deposited GO film, 50 ~ 60 nm in thickness, was found to have a Young's modulus of 695 ± 53 ~ 697 ± 15 GPa. The critical energy values for 50- and 60-nm-thick films were 0.142 ~ 0.201 and 0.479 ~ 0.596 J/m², respectively. Nanoindentation combined with the DCM can thus be used to obtain the mechanical properties and critical energy of thin films.     

Fabrication of amperometric biosensors by entrapment of enzymes in functionalized polypyrrole films

The concept and potentialities of an original electrochemical procedure of enzyme immobilization are described. This two-step method consists of the adsorption of an aqueous amphiphilic pyrrole monomer-enzyme mixture on an electrode surface followed by the electropolymerization of the adsorbed monomers. This procedure is compared with the conventional electrochemical methods of biosensor construction. Several bienzyme electrodes devoted to the improvement of the biosensor selectivity or to the amplification of the biosensor sensitivity are described. In addition, examples of organic phase enzyme electrode and the electrical wiring of immobilized enzymes are presented.     

PANI/煤基石墨烯宏观体复合材料的制备及其电化学性能

以太西无烟煤为原料,采用催化热处理、改良Hummers氧化等方法,制备煤基氧化石墨烯（CGO）,进而以CGO和聚苯胺（PANI）为前驱体,采用水热自组装法,制备得到PANI/石墨烯宏观体复合材料（3D-PCG）。采用FT-IR、XRD、Raman、SEM和TEM等技术,研究了材料的组成、结构和形貌,考察了3D-PCG的电化学性能。结果表明,PANI以纳米棒状形态均匀镶嵌在煤基石墨烯宏观体（3D-CG）的网状结构中;当PANI与CGO质量比为1：2时,3D-PCG的电化学性能优于PANI和3D-CG,其比电容可达663 F·g^-1。     

锂硫电池石墨烯/纳米硫复合正极材料的制备及电化学性能

利用热解还原将Hummers法制得的氧化石墨烯还原为石墨烯,并采用化学沉淀法将纳米硫成功负载到石墨烯片层上,获得石墨烯/纳米硫（RGO/nano-S）正极复合材料。利用FT-IR、XRD、SEM、TEM和Raman对所制备复合材料的微观结构、形貌等进行表征,采用恒流充放电、循环伏安法和交流阻抗法对复合材料的电化学性能进行研究。研究结果表明,热还原所得石墨烯褶皱的表面形成容纳硫及多硫离子的空间,有助于缓解活性物质溶解和抑制多硫离子迁移;同时,均匀分布的纳米硫能更好地与电解液接触,在石墨烯的导电网络上增大了电化学反应面积,进而改善了该材料作为锂硫电池的实际放比电容量和倍率循环性能。     

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.     

硅/石墨烯基自支撑薄膜的制备及电化学性能

采用简单的超声、抽滤和水合肼化学还原相结合的方法制备硅/石墨烯基自支撑薄膜,系统研究了硅含量对硅/石墨烯复合材料电化学性能的影响。结果表明：通过在石墨烯水凝胶的片层之间插入纳米硅颗粒,可以有效地控制硅体积变化,增加该复合膜的机械强度并提高其导电性。提高硅/石墨烯复合材料中硅含量的比例可以提升其可逆比容量和首次库仑效率,当硅质量分数为53%时,复合膜在0.1C倍率下的可逆比容量及首次库仑效率分别达到945.6mA·h/g和64.8%（纯硅的229倍和9倍）;继续提高硅含量的比例,可以提升其循环寿命（循环50次容量保持率60.9%、质量分数为67%的Si）,但材料比容量有所下降,说明石墨烯在稳定硅基复合材料电化学性能方面发挥着非常重要作用。     

Fabrication of self-binding noble metal/flexible graphene composite paper

Self-binding noble metal (Pt, Au, and Ag)/graphene composite papers as large as 13 cm in diameter were fabricated using a flow-directed method where in situ reduced graphene served as a “binder”. The papers were characterized by X-ray diffraction, scanning and transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. This approach yielded well dispersed metals with various nanostructures both on and between the graphene layers to form papers with good conductivity and flexiblility. The 300 °C-annealed Ag/graphene papers were evaluated as binder-free anodes for lithium ion batteries, delivering a reversible charge capacity of 689 mAh/g at a current density of 20 mA/g.     

Gold nanoparticle-based electrochemical biosensors

The unique properties of gold nanoparticles to provide a suitable microenvironment for biomolecules immobilization retaining their biological activity, and to facilitate electron transfer between the immobilized proteins and electrode surfaces, have led to an intensive use of this nanomaterial for the construction of electrochemical biosensors with enhanced analytical performance with respect to other biosensor designs. Recent advances in this field are reviewed in this article. The advantageous operational characteristics of the biosensing devices designed making use of gold nanoparticles are highlighted with respect to non-nanostructured biosensors and some illustrative examples are commented. Electrochemical enzyme biosensors including those using hybrid materials with carbon nanotubes and polymers, sol-gel matrices, and layer-by-layer architectures are considered. Moreover, electrochemical immunosensors in which gold nanoparticles play a crucial role in the electrode transduction enhancement of the affinity reaction as well as in the efficiency of immunoreagents immobilization in a stable mode are reviewed. Similarly, recent advances in the development of DNA biosensors using gold nanoparticles to improve DNA immobilization on electrode surfaces and as suitable labels to improve detection of hybridization events are considered. Finally, other biosensors designed with gold nanoparticles oriented to electrically contact redox enzymes to electrodes by a reconstitution process and to the study of direct electron transfer between redox proteins and electrode surfaces have also been treated.     

Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

钛酸锂/石墨烯复合材料及电化学性能

通过固相法制备出钛酸锂(LTO)样品,再将LTO和氧化石墨烯通过水热法制得钛酸锂/还原石墨烯复合材料(LTO-RGO)。通过XRD、SEM、TEM对材料的结构、形貌进行表征,并进行充放电性能测试、交流阻抗测试来检测其电化学性能。结果表明,石墨烯对钛酸锂进行包覆处理不影响钛酸锂材料的晶型结构、无杂相出现。钛酸锂/石墨烯复合材料表现出了比钛酸锂材料更为优异的电化学性能,0.2C倍率下的放电比容量为208.7mA·h/g,50次循环后容量保持率为98.10%;20C倍率下的放电比容量为136.1mA·h/g。     

Fabrication of graphene/single wall carbon nanotubes/polyaniline composite gels as binder-free electrode materials

A three-dimensional (3D) graphene-based hydrogels system containing one-dimensional (1D) carbon material-single wall carbon nanotubes (SWCNTs) and pseudocapacitor material-polyaniline (PANI) was prepared by combination of cross-linking, reduced and in situ polymerization. The polyaniline nanoparticles were combined with the reduced graphene sheet by π-π conjugation. The as-perpared composite gels could be directly used as electrode materials without binders. Due to the synergistic effect between SWCNTs, graphene sheet and PANI, the graphene/single wall carbon nanotubes/polyaniline (GH/SWCNTs/PANI) composite gel shows the enhanced electrochemical performances. The resultant GH/SWCNTs/PANI gel electroactive material shows a gravimetric specific capacitance of 145.4 F/g at 0.5 A/g and has improved 45% compared with initial graphene hydrogel (GH) at the same current density. And it keeps high retention of 98.8% of the initial capacity after 10,00 charge/discharge cycles at high current density of 10 A/g. The great cycle stability achieved is fundamentally attributed to the support of graphene sheet and single wall carbon nanotubes, which favors stress distribution and charge transfer during the longtime charge/discharge process. The graphene-based hydrogels could be a potential applicant for high rate charge/discharge applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46948.     

Fabrication of in-plane aligned carbon nanotube-polymer composite thin films

In-plane aligned carbon nanotube-polymer composite thin films with submicrometer thickness on unmodified SiO₂ surfaces are fabricated using the spincoating alignment technique, which is simple, integratable to the manufacture process of organic devices, and applicable to various matrix polymers (e.g. polycarbonate and polythiophene). Controlled manipulation of the nanotube alignment in a polymer matrix is an effective method to tune the electrical conductivity of a 5 wt.% single-walled carbon nanotube-polycarbonate composite film spanning nearly four orders of magnitude.     

Electrosynthesis of polyaniline-based composite films and their electrochemical activity

Herein, we report the synthesis of organic–inorganic hybrids of polyaniline-rGO-ZnO (PRZ) ternary composite materials for a potential application in dye-sensitized solar cell (DSSC). A facile all-electrochemical method was adopted for the deposition of PRZ films on FTO-coated glass substrate. The PRZ hybrid assembly was subsequently characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry, and photoelectrochemical measurements. Further, the morphological and elemental composition features of PRZ were monitored by field emission SEM and EDX, respectively. Electrochemical impedance spectra suggest that the charge–transfer resistance for the ternary composite is distinctly decreased. The maximum conversion efficiency of DSSC with PRZ counter electrode reaches 2.84%, which is higher than that of polyaniline-reduced graphene oxide (rGO) counter electrode. This ternary composite (PRZ) with organic–inorganic hybrid architecture showing an enhanced photoelectrochemical activity might be exploited in future as a promising material for application in next-generation solar devices.     

Electrochemical synthesis of melanin free-standing films

Free-standing melanin films were successfully synthesised electrochemically from dopa. The optimum synthetic conditions such as pH, concentration and current were determined, and it was found that free-standing films could only be formed when ITO glass electrodes were used. The films were analysed by solid state NMR and XPS which showed the presence of indolic moieties characteristic of melanin-type macromolecules. The film showed higher conductivity than chemically synthesised melanin previously reported in literature and also exhibited photoconductivity.     

Sulfur-incorporated,porous graphene films for high performance flexible electrochemical capacitors

Graphene and its derivatives are considered potential electrode materials for flexible electrochemical capacitors (f-ECs), but their capacitive performances have to be improved for practical applications. Herein, we demonstrate fabrication of flexible sulfur (S)-incorporated reduced graphene oxide (SRGO) electrodes obtained by pyrolyzing free-standing film consisting of benzyl disulfide-functionalized graphene oxides at 900 °C. The effect of S incorporation on morphology and chemical structure of SRGO were investigated by various microscopic and spectroscopic methods. Incorporation of S and the crumpled and porous morphology of SRGO electrodes improve capacitive performance of f-ECs; SRGO f-ECs show a specific capacitance of 140.8 F/g at 1 A/g, rate capability of 91.5% retention, and cyclic performance of 93.4% after 1000 charge/discharge cycles at 4 A/g. Impressively, SRGO f-ECs exhibit excellent electrochemical and mechanical durability after 1000 charge/discharge cycles at a bending angle of 120° with values that greatly exceed those of conventional RGO-based f-ECs. This study provides a fundamental foundation of the correlation between S composition of carbon nanomaterials and their electrochemical (or surface) properties.     

孔状氧化锌/石墨烯复合材料制备及其电化学性能研究

以氧化石墨烯和醋酸锌为原料,N,N’-二甲基甲酰胺为溶剂,采用溶剂热法制备了孔状氧化锌/石墨烯的复合材料。通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)等对氧化锌/石墨烯复合材料的微观形貌结构和成分进行分析,并通过循环伏安、恒流充放电和交流阻抗对电学性能进行测试,结果表明,采用溶剂热法成功制备孔状氧化锌/石墨烯复合材料,带孔微球氧化锌均匀分散于薄纱状石墨烯表面,在6 mol/L KOH电解液中有良好的电容性能,当扫描速度为5 m V/s时,比电容为256.9 F/g。