Highly conductive graphene by low-temperature thermal reduction and in situ preparation of conductive polymer nanocomposites

Polydopamine-coated graphene oxide (DGO) films exhibit electrical conductivities of 11?000 S m(-1) and 30?000 S m(-1) upon vacuum annealing at 130 °C and 180 °C, respectively. Conductive poly(vinyl alcohol)/graphene and epoxy/graphene nanocomposites show low percolation thresholds due to the excellent dispersibility of the DGO sheets and their effective in situ reduction.     

Annealing a graphene oxide film to produce a free standing high conductive graphene film

A free-standing graphene oxide film (GOF) obtained by self-assembly at a liquid/air interface was annealed in a confined space between two stacked substrates to form a free-standing highly conductive graphene film. Characterization indicates that the oxygen-containing functional groups (e.g. epoxy, carboxyl, and carbonyl) were removed as small molecules (e.g. H₂O, CO₂, and CO) during the annealing, meanwhile the size of sp² domains in the film was decreased. When annealed between two stacked wafers, random interlayer expansion and fractional movement in the GOF were suppressed by the pressure-induced friction, which helps preserve the morphology of the film. The conjugation in the basal plane of graphene and π–π interactions between well stacked graphene sheets favor the transportation of charge carriers in the film, to produce a good electrical conductivity of the resulting free-standing reduced GOF (increased from 1.26 × 10^?5 to 272.3 S/cm).     

石墨烯改性导电胶的制备及导电机理研究

以环氧树脂(EP)为基体、聚苯胺为助剂、铜粉为导电填料和石墨烯为改性剂,采用共混法制备了高导电性、高粘接强度、低成本和固化后不易开裂的导电胶,并对其导电机理进行了分析。研究结果表明:铜粉作为导电填料,可使导电胶的成本大幅降低,当w(铜粉)=60%(相对于EP质量而言)时,导电胶的导电性能相对最佳(体积电阻率为4.14×10~(-3)Ω·cm)。石墨烯可进一步改善导电胶的导电性能,当w(石墨烯)=0.05%(相对于EP质量而言)时,导电胶的体积电阻率(2.78×10~(-3)Ω·cm)相对最低。石墨烯在胶体内形成类似钢筋骨架作用的网络结构,使填料之间连接更紧密,从而有效提高了导电胶的导电性能和力学性能,解决了导电胶固化后易开裂、韧性不足等难题。     

In situ chemical reduction and functionalization of graphene oxide for electrically conductive phenol formaldehyde composites

We report an efficient one-step approach to reduce and functionalize graphene oxide (GO) during the in situ polymerization of phenol and formaldehyde. The hydrophilic and electrically insulating GO is converted to hydrophobic and electrically conductive graphene with phenol as the main reducing agent. Simultaneously, functionalization of GO is realized by the nucleophilic substitution reaction of the epoxide groups of GO with the hydroxyl groups of phenol in an alkali condition. Different from the insulating GO and phenol formaldehyde resin (PF) components, PF composites are electrically conductive due to the incidental reduction of GO during the in situ polymerization. The electrical conductivity of PF composite with 0.85 vol.% of GO is 0.20 S/m, nearly nine orders of magnitude higher than that of neat PF. Moreover, the efficient reduction and functionalization of GO endows the PF composites with high thermal stability and flexural properties. A striking increase in decomposition temperature is achieved with 2.3 vol.% of GO. The flexural strength and modulus of the PF composite with 1.7 vol.% GO are increased by 316.8% and 56.7%, respectively.     

Hyperbranched polysiloxane-modified UV-curable graphene conductive coatings: preparation and characterization

A new UV-curable hyperbranched silicone epoxy acrylate resin was synthesized, and two kinds of carbon-based components, graphite and graphene, were applied as conductive materials. An ultraviolet-curing coating was successfully synthesized with using epoxy acrylate (EA) as oligomer, butyl acrylate (BA), and hyperbranched polysiloxane (HPSi) as monomers, benzoin dimethyl ether (DMPA), and benzophenone (BP) as photo-initiators, triethanolamine (TEA) as photo-activator, and other auxiliaries. In this work, the UV-curing efficiency and cured performance, together with the effect of different conductive fillers and the amount of conductive filler on the integrated performance of the composites, are investigated. The results show that as the HPSi content increases, the curing time is shortened. At the addition amount of 7.5%, it reaches the best conductivity, and at the addition amount of 10%, the corrosion resistance after curing is the best. However, the maximum tensile strength of 10.4% is obtained at 0.75 graphene. The FE-SEM micrographs of the UV-curable conductive coating show that with increasing incorporation of graphene into the substrate, the fractured surface of a rough surface changes to smooth one. Thermal properties of the films investigated using TGA curves indicate that graphene-doped conductive adhesive film (315.1 °C) possesses much higher heat resistance than that of graphite-doped conductive adhesive film.     

Indium metal-organic framework with catalytic sites coated conductive graphene for high-performance lithium-sulfur batteries

Metal-organic frameworks (MOFs) with abundant active sites and stable frame structures have great advantages for inhibiting the "shuttle effect" and alleviating volume expansion in lithium-sulfur (Li–S) batteries. However, their inherent poor conductivity hinders their application in Li–S batteries. Herein, with isophthalic acid (IPA) as the organic ligand and indium ions as the central metal, a tetrahedral cubic indium MOF (In-IPA) was synthesized and employed for the first time as a sulfur host. Experimental results suggest that In-IPA has a good catalytic effect on the conversion of polysulfides. Furthermore, three-dimensional In-IPA was coated with reduced graphene oxide (rGO) by the hydrothermal method (In-IPA@rGO). The interlaced rGO network not only significantly enhances the conductivity of In-IPA but also improves the reduction of kinetic reactions and promotes electron transport. Finally, In-IPA@rGO exhibited excellent electrochemical performance as a sulfur host. In particular, it exhibited a considerable initial capacity of 1672.3 mAh g^?1 at 0.2 C and a reversible capacity of 898.7 mAh g^?1 after 100 cycles. In addition, the initial capacity reached 1376.7 mAh g^?1 and retained 519.8 mAh g^?1 after 200 cycles at 0.5 C. This work proves that nontransition metal-organic frameworks prepared along with highly conductive rGO have synergistic advantages in Li–S battery applications.     

化学导电氧化膜防护性的提高

介绍了铝及其合金化学导电氧化工艺规范及工艺流程,采用正交试验法研究了氧化时间、铬酐含量、溶液温度、烘干温度对导电氧化膜色泽的影响,获得最佳工艺参数。试验证明,该化学导电氧化膜外观色泽鲜艳一致,防护性明显增强。     

PEDOT:PSS导电自支撑薄膜的合成与制备

以3,4-乙烯二氧噻吩（EDOT）为原料，聚对苯乙烯磺酸钠（PSS-Na）为分散剂和掺杂剂，通过化学氧化合成法在水体系中聚合制备了聚(3,4-乙烯二氧噻吩):聚苯乙烯磺酸（PEDOT:PSS）悬浮液，通过真空抽滤的方法制备了PEDOT:PSS自支撑柔性导电薄膜。通过FTIR、UV-Vis对聚合产物结构进行了表征与确认，通过四探针电导率测试、SEM、拉伸断裂强度测试对PEDOT:PSS薄膜的导电性、微观形貌与力学性能进行了表征。结果表明，成功制备了PEDOT:PSS目标产物，在氧化剂与单体物质的量之比为0.875时达到最佳电导率（19.19 S/cm）。自支撑薄膜厚度约18 μm，在25 ℃，40%~60%相对湿度范围内拉伸断裂强度达到45~60 MPa，具有良好的导电性与机械性能。     

Direct reduction of graphene oxide films into highly conductive and flexible graphene films by hydrohalic acids

We report a simple but highly-effective hydrohalic acid reducing method to reduce graphene oxide (GO) films into highly conductive graphene films without destroying their integrity and flexibility at low temperature based on the nucleophilic substitution reaction. GO films reduced for 1 h at 100 °C in 55% hydroiodic (HI) acid have an electrical conductivity as high as 298 S/cm and a C/O ratio above 12, both of which are much higher than films reduced by other chemical methods. The reduction maintains good integrity and flexibility, and even improves the strength and ductility, of the original GO films. Based on this reducing method, a flexible graphene-based transparent conductive film with a sheet resistance of 1.6 kΩ/sq and 85% transparency was obtained, further verifying the advantage of HI acid reduction.     

Large-size graphene microsheets as a protective layer for transparent conductive silver nanowire film heaters

A new strategy is reported for the fabrication of silver nanowire (AgNW) film heaters using reduced small/or large-size graphene oxide (rSGO or rLGO) sheets as an over-coating protective layer. The results show that ultrathin rLGO microsheets provide the best combination of protective effect and electrical properties on AgNW networks and thus could enable the design of high-performance transparent film heaters. As a consequence, good optical transparency and electrical conductivity, good oxidation resistance and thermal stability, and good heating performances are achieved with as-made rLGO/AgNW film heaters. Specifically, the rLGO/AgNW hybrid film annealed at 700 °C shows a low sheet resistance of 27 Ω sq⁻¹ and a good optical transparency of 80%. Furthermore, it exhibits good heating characteristics and defrosting performance at low voltages. The results presented here may pave the way for a new promising application of rLGO/AgNW hybrid film in transparent film heaters and other electrical devices.     

Simultaneous surface functionalization and reduction of graphene oxide with octadecylamine for electrically conductive polystyrene composites

Simultaneous surface functionalization and reduction of graphene oxide (GO) was realized by simple refluxing of GO with octadecylamine (ODA) without the use of any reducing agents. The presence of the long octadecyl chain made the hydrophilic GO hydrophobic, evidenced by the selective dispersion of the ODA-functionalized GO (GO–ODA) in chloroform solvent rather than in water. Interestingly, different from the insulating GO, GO–ODA became electrically conductive due to the reduction in the presence of ODA. The electrical conductivity of GO–ODA was further increased by incidental thermal reduction during the compression-molding of its polystyrene (PS) composites at 210 °C, which exhibited a sharp transition from electrically insulating to conducting with a low percolation threshold. The high conductivity of the PS/GO–ODA composites is attributed to the improved dispersion and the reduction of GO–ODA in comparison with GO.     

One-step chemical reduction of graphene oxide with oligothiophene for improved electrocatalytic oxygen reduction reactions

Oligothiophene (nTP, n = 1, 2, 3) has been used as the reductant for the first time in the preparation of graphene by the reduction of graphene oxide (GO). A simple single-step chemical approach has been developed to reduce and/or functionalize GO with nTP. The reaction takes place at room temperature under stirring of a suspension of GO and nTP in MeCN. The nTP has been grafted onto the surface of GO by reacting epoxy groups together with the reduced graphene oxide (rGO). It was observed that increasing the thiophene ring (hereafter, thiophene is referred to as TP; 2,2′ bithiophene as 2TP; and 2,2′:5′,2″ terthiophene as 3TP) can enhance the reduction reaction. All instrumental experiments have confirmed that nTP not only covalently bonded to the GO but also partly restored the conjugate structure of GO, as a reducing agent. The resultant rGO with 3TP (rGO3TP) has been demonstrated to show remarkable electrocatalytic activity toward oxygen reduction reaction (ORR) compared to typical rGO. The observed ORR electrocatalytic activity induced by the intermolecular charge-transfer provides a general approach to various carbon-based metal-free ORR catalysts.     

石墨烯/导电聚合物复合防腐蚀材料制备及应用研究进展

石墨烯/导电聚合物复合材料不仅具有石墨烯优异的屏蔽性能和导电聚合物良好的氧化还原特性,还能协同发挥二者的功能,在金属防腐蚀领域有着巨大的应用潜力。本文综述了石墨烯/导电聚合物复合防腐蚀材料的制备方法,包括电化学方法、化学氧化法、分散液混合法和化学气相沉积法（CVD）;并全面总结了石墨烯/导电聚合物复合材料在防腐蚀涂层中的应用及性能。制备的石墨烯/导电聚合物复合材料可以通过电化学方法、溶剂挥发法制成石墨烯/导电聚合物防腐蚀薄膜涂层,还可以混入成膜物树脂中制备树脂复合防护涂层。讨论了石墨烯/导电聚合物在制备过程、薄膜涂层和树脂复合涂层应用中的优势与不足,提出了构建结构可控、综合性能好的复合防腐涂层是石墨烯/导电聚合物复合防腐蚀材料的未来主要发展趋势。     

还原法制备石墨烯的研究进展及发展趋势

综述了还原法制备石墨烯的研究现状,主要介绍了金属还原、光催化还原、电化学还原、热还原、化学还原试剂还原等方法的研究进展,并指出了还原法制备石墨烯的发展趋势。     

氧化石墨烯/密胺树脂导电复合材料的制备与性能研究

采用的改进的Hummers法和组合剥离技术制备了氧化石墨烯(GO),并以氧化石墨烯、甲醛溶液、三聚氰胺为原料,采用原位合成技术制备石墨烯/密胺树脂导电复合材料(GO/MF)及含有水合肼的氧化石墨烯/密胺树脂复合材料(GO/MF+N_2H_4),并对其结构、热稳定性和导电性等进行研究分析。试验结果表明:GO/MF+N_2H_4试样的热稳定性最佳,氧化石墨烯的加入,提高了密胺树脂材料的导电性,且添加质量分数0.9%GO的GO/MF+N_2H_4试样出现导电临界值,体积电阻率达到1.5×10~4Ω·m,为制备具有抗静电性能和导电性能的密胺树脂新型复合材料提供一定的基础理论参考。     

Large scale production of highly conductive reduced graphene oxide sheets by a solvent-free low temperature reduction

A novel one-pot process that can produce freestanding reduced graphene oxide (RGO) sheets in large scale through a mechanochemical method is presented, which is based on a 1:1 adduct of hydrazine and carbon dioxide (H₃N⁺NHCO₂⁻, solid hydrazine). We were able to synthesize RGO sheets by grinding solid hydrazine with graphene oxide (GO), followed by storing the mixed powder at 50 °C for 10 min. No solvents, nor large vessels, nor post-annealing at high temperatures are required. The resulting RGO sample was characterized by elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller measurement, thermo gravimetric analysis, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance spectroscopy, and conductivity measurement. It exhibits excellent conductivity and possesses a high specific surface area. This reduction method was successfully applied for the fabrication of inkjet-printed RGO devices on a flexible substrate.     

Reduction of graphene oxide films on Al foil for hybrid transparent conductive film applications

We report the reduction of graphene oxide (G-O) films on Al foil using hydrogen as a reducing agent generated during the etching of Al foil in an aqueous solution of hydrochloric acid (HCl). Complete etching of the Al substrate results in simultaneous reduction and a free standing film composed of stacked and overlapped reduced graphene oxide (RG-O) platelets. Generation of hydrogen at the G-O/Al interface increases the reduction efficiency of this method that is demonstrated in better electrical conductivity of the obtained films compared to the RG-O films reduced by the similar method but using remote Al foil in HCl solution and hydrazine reduced RG-O films. By transferring the free standing RG-O films onto Ag NW films, hybrid transparent conductive films (TCFs) with opto-electrical properties comparable to that of ITO films were obtained.     

A preparation approach of exploring cluster ion implantation: from ultra-thin carbon film to graphene

Based on the extensive application of 2 × 1.7MV Tandetron accelerator, a low-energy cluster chamber has been built to explore for synthesizing graphene. Raman spectrum and atomic force microscopy (AFM) show that an amorphous carbon film in nanometer was deposited on the silicon by C₄ cluster implantation. And we replaced the substrate with Ni/SiO₂/Si and measured the thickness of Ni film by Rutherford backscattering spectrometry (RBS). Combined with suitable anneal conditions, these samples implanted by various small carbon clusters were made to grow graphene. Results from Raman spectrum reveal that few-layer graphene were obtained and discuss whether I_G/I_2D can contribute to explain the relationship between the number of graphene layers and cluster implantation dosage.