【作者】 常云珍；

【导师】 韩高义；

【作者基本信息】 山西大学 ， 无机化学， 2013， 博士

【摘要】 石墨烯是由sp2杂化的C组成,具有单原子层厚度的二维碳材料。从2004年被Geim等科学家发现以来,由于其极好的机械强度、超高的载流子速率和热导率,激发了理论和实验科学家们极大的研究兴趣,在电子学、复合物、催化、能源储存等领域得到广泛应用。目前,化学还原氧化石墨烯被认为是一种操作简单、成本低、可大量制备石墨烯的有效方法,寻求安全、高效、环保的还原剂并研究其还原机理仍然是研究的一个热点问题。另外,将石墨烯分散在水中容易发生不可逆的团聚。因此,通过控制形貌、化学掺杂和化学腐蚀可以有效调控石墨烯的性质,拓展其应用领域。本论文,基于石墨烯的材料化学,对石墨烯的制备、掺杂、组装和电化学性能进行了系统的研究。主要内容和结果如下：(1)在低于200℃的温度下,以甲醛、甲酸为还原剂,将氧化石墨烯(GO)与还原剂蒸气反应(气相反应)或者与液态还原剂进行溶剂热反应(液相反应),分别研究了还原剂用量,还原温度和还原时间对化学还原石墨烯(rGOs)电导率的影响,并通过X-射线衍射(XRD), X射线光电子能谱(XPS)和拉曼光谱进行表征和分析。实验结果表明：当气相反应的最佳还原温度为150℃,而液相反应的最佳还原温度为175℃时,GO得到最大程度的还原。当反应时间增加到24h,气相反应制备的rGOs的氧原子百分含量明显增加,而液相反应制备的rGOs的氧原子百分含量增加不明显,甚至有减少的趋势。而且,石墨烯电导率与其所含的C、O原子比有一定的关系。(2)分别以羟胺和盐酸羟胺作为还原剂和N掺杂剂,与GO进行溶剂热反应制备N掺杂的石墨烯水凝胶(NGHs),并通过扫描电子显微镜、XRD、XPS、拉曼光谱对样品进行表征。在25%KOH电解液中,采用两电极法测试基于NGHs的超级电容器电容性能。实验结果表明：NGHs的形貌、电导率和N掺杂量受还原剂种类和用量、反应温度、反应时间的影响。以羟胺为还原剂,在150℃溶剂热反应12h得到NGHs(NGH-HA12)的N原子百分比为4.32%。当循环伏安扫描速度为1.0mV s-1时,NGH-HA12电极材料比电容为205F g-1,具有较好的循环稳定性。当基于NGH-HA12电极材料的超级电容器的充放电电流密度为100Ag-1,能量密度为3.65Wh kg-1时,其功率密度为20.5kW kg-1。(3)通过“羟胺扩散诱导组装”法可以制备出多种大面积N掺杂石墨烯基纸和透明薄膜,包括N掺杂石墨烯纸(NG-P)、N掺杂石墨烯和碳纳米管复合纸(NG-CNT-P)、沉积到基底表面的N掺杂石墨烯透明薄膜(NG-TP)以及其复合透明薄膜。在整个实验过程中,GO成型、还原和N掺杂一步完成。制备的NG-P拉伸强度可达到70.0MPa,杨氏模量可达到17.7GPa。NG-P经过300℃处理2h (NG-P300)后,其热导率高达3403W m-1K-1。在1M的H2SO4电解液中,用两电极法测试基于NG-P300的超级电容器的电化学性能。实验结果表明：当循环伏安扫描速度高达800V s-1时,其CV曲线仍然能保持较好的矩形。频率为120Hz时,其相位角-77.1°。制备的NG-TP在550nm的透光率为78%时,其面电阻可达大约4000Ω/□。(4)用类似“羟胺扩散诱导组装”的方法,通过湿法纺丝制备大面积N掺杂石墨烯纤维膜(NG-FM)。制备的NG-FM表现出较好的柔韧性。NG-FM经过300℃处理2h (NG-FM300)后,在25%KOH电解液中,用两电极法测试基于NG-FM300的超级电容器的电容性能。实验结果表明：当循环伏安扫描速度为5.0m Vs-1时,NG-FM300电极材料的比电容188Fg-1。当扫描速度高达10V s-1时,其比电容值仍然能保留最初比电容值的51%。基于NG-FM300的超级电容器的能量密度为3.1Wh kg-1时,功率密度高达114,000W kg-1。(5)结合静电纺丝、表面修饰和高温碳化技术,制备具有导电性高和柔韧性好的石墨烯修饰碳纤维复合纳米纤维膜(GCFM)。以此为载体,用甲醛蒸气还原吸附到GCFM上的H2PtCl6·6H2O,将Pt纳米粒子沉积到GCFM表面,得到Pt-GCFM催化电极,并对其进行结构表征和电催化氧化甲醇性能测试。实验结果表明：与Pt-CFM(用相同方法将Pt纳米粒子沉积到CFM电极表面)和Pt/C-GCFM(商用Pt/C底涂到GCFM表面)催化电极相比,Pt-GCFM催化电极表现出最好的电催化氧化甲醇的活性、稳定性和抗中毒能力。特殊结构的GCFM有利于提高Pt纳米催化剂电催化氧化甲醇的活性和稳定性,说明GCFM是一种很有潜力的电催化剂载体。更多还原

【Abstract】 Graphene, a kind of two-dimensional carbon material constructed by layers of sp2-bonded carbon atom, exhibits applications in fields of electronics, composite materials, catalysis, energy generation and storage etc owing to its extreme mechanical strength, exceptionally high electron mobility and thermal conductivities and has stimulated tremendous attention for both the experimental and theoretical scientific communities in recent years since it was discovered at2004by Geim. Graphene produced through chemically reducing graphene oxide obtained from graphite is considered to be the more efficient, inexpensive and simpler approach to large-scale use, it is still the hot issues to seek the safe, efficient, pollution-free reducing agent and study its mechanism. However, graphene dissolved in water prone to an irreversible coagulation and affect the performace of the graphene. Therefore, the morphology control, chemical doping and etching are effective approach to tune the property of graphene and greatly expand their applications. In this dissertation, based on the materials chemistry of graphene, the preparation, doping, assembly and their electrochemical properties of graphene-based materials were investigated. The main contents and results are summarized as follows:(1) GO being exposed to a vapor and liquid phase of formaldehyde and formic acid at a reaction temperature below200℃were studied using XRD, XPS and Raman spectroscopy. The reducing agent concentration, reducing temperatures and time intensively affect the electrical conductivity of chemically reduced graphene (rGOs). Significant reduction of GO was observed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), with the largest extent of reduction obtained at150℃in vapor phase and at175℃in liquid phase. In addition, with the increase of reaction time such as24h, O content of rGO increase obviously when it obtained in vapor phase while the O content increases slightly or even decrease for rGO obtained in solution of the reductant. It is reveals that the atomic ratio of C to O has some correlation to the electrical conductivity of rGO.(2) N-doped graphene hydrogels (NGHs) could be obtained by using hydroxylamine hydrochloride and Hydroxylamine (HA) as the chemical dopant and reductant through a simple solvothermal reaction. The products were characterized by scanning electron microscope, XRD, XPS, Raman spectroscopy and electrochemistry. The results showed that the electrical conductivity, microstructure and doping level of NGHs were influenced by the type and quantity of reductants, temperature and time of the reaction. The NGHs prepared at150℃for12h using HA as reductant (NGH-HA12) had a N-doping level of4.32%in atom and exhibited a specific capacitance of205F g-1and good cycling stability. The energy density and power density could reach3.65Wh kg-1and20.5kW kg-1at a discharge of100A g-1for the symmetric capacitor assembled by NGH-HA12in25%KOH electrolyte using the two-electrode symmetric capacitor test.(3) Various N-doped graphene-based materials with large area, including N-doped graphene paper (NG-P), N-doped graphene and carbon nanotubes composite paper (NG-CNT-P), N-doped graphene transparent films (NG-TF) and the composite transparent films deposited on substrates, are prepared using a facile approach named as "hydroxylamine diffusing inducing assembly (HDIA)". The molding of GO is carried out at room temperature, the reduction of graphene oxide and the N-doping are achieved simultaneously under atmospheric pressure and at low temperature (100℃). The NG-P treated at100℃for10h possesses a tensile stress of about70.0MPa and Young’s modulus of about17.7GPa. Using the two-electrode symmetric capacitor test, ultrahigh-rate capacitors assembled by NG-P treated at300℃for2h (NG-P300) still show rectangle-liked CV curves at scan rate of800V s-1and exhibit a phase angle of-77.1°at frequency of120Hz in1M H2SO4electrolyte, thermal conductivity of NG-P300is calculated to be about3403.39W m-1K-1. The surface resistivity of NG-TP can reach up to4000Ω/a at78%transmittance (550nm).(4) Using the similar process, larger-scale N-doped graphene fiber mats (NG-FM) are prepared using the "hydroxylamine diffusing inducing assembly (HDIA)" The obtained NG-FM exhibits good flexibility. Using the two-electrode symmetric capacitor test, the obtained NG-P treated at300℃for2h (NG-FM300) possesses a specific capacitance of188F g-1at scan rate of5mV s"1and can retain Ccs51%at10V s-1, the energy density of capacity assembled by NG-FM300can reach to3.1Wh kg-1at a power density of114,000W kg-1in25%KOH.(5) Carbon fibre mats modified by graphene (GCFMs) have been fabricated by combining the electrospinning, thermal treatment and surface decoration. Pt particles were deposited on the GCFM using formaldehyde vapor react with H2PtCl6·6H2O on the GCFM. The electrochemical catalytic electrodes are characterized and evaluated. The results show that the Pt catalyst loaded on GCFM possesses high electrocatalytic activity, good tolerance towards reaction intermediates and unusually high stability towards methanol electrocatalytic oxidation compared with Pt-CFM (the Pt catalyst loaded on CFM) and Pt/C-GCFM(commercial Pt/C doped to GCFM)catalytic electrodes. It is found that the special structure of the GCFM is favorable for the activity and long-term stability of the Pt catalyst towards methanol electro-oxidation, indicating that the GCFM is a hopeful candidate to be developed as an excellent supporting material for electrochemical catalysts.更多还原