石墨烯基三维结构纳米材料的制备及在电化学能源中的应用

发布时间：2018-01-06 14:06

本文关键词：石墨烯基三维结构纳米材料的制备及在电化学能源中的应用　出处：《湖南大学》2015年博士论文　论文类型：学位论文

【摘要】：开发高性能的“绿色”电化学能源器件是有效解决人类目前所面临“能源危机”和“环境污染”两大难题的重要途径,而其电极材料是影响器件电化学性能的关键因素之一。因此,设计合成性能优异的电极材料将具有重要意义和学术价值。近年来,石墨烯由于具有优异电学和力学性能以及高比表面积等特点,使得石墨烯和石墨烯基纳米材料在电化学能源中的应用研究备受关注,如超级电容器、锂电池以及燃料电池等领域。然而利用氧化石墨烯(GO)制备还原氧化石墨烯(RGO)或合成宏观石墨烯基复合材料的过程中RGO容易发生团聚,这导致其比表面积远低于理论值、电活性位点减少且不利于电活性物质的电子传递及电解液荷电组分的迁移和扩散,使得石墨烯或石墨烯基复合材料的电化学性能没有达到预期的增强效果。构筑三维结构石墨烯或石墨烯基纳米材料将有效提高石墨烯比表面的利用率、增多电活性位点、加速电子传递、便于电解液渗透和离子输运,从而将有望改善石墨烯基纳米材料的电化学性能。因此,本论文设计并合成几类石墨烯基三维结构纳米材料,研究其在超级电容器、燃料电池阴极和锂硫二次电池中的应用,探索结构与性能之间的关系。主要研究内容和创新点如下:(1)采用水热法制备还原氧化石墨烯/碳纳米管/氢氧化镍(RGO/CNTs/Ni(OH)2)三元复合材料。结构表征结果显示5-10 nmα-Ni(OH)2粒子嵌入三维结构的RGO/CNTs复合物形成相应的复合材料(GC2N2)。研究表明,电极材料GC2N2展现了高比电容、优异倍率性能和循环稳定性。此外,将GC2N2和多孔RGO/CNTs(p GC)材料组装成不对称电容器,其电容可达75 F g-1(20 A g-1电流密度下放电),能量密度和功率密度分别为30.1 Wh kg-1和17.0 k W kg-1。电容性能和循环稳定性的提高主要归因于碳纳米管插入石墨烯层间形成的三维导电网络结构,既有利于电解液的渗透和扩散,又有利于电荷传输和电子传递,同时有效地阻止活性物质的团聚和缓解了体积膨胀、收缩。(2)运用模板法制备三维结构多孔石墨烯中空球框架,并在其框架材料上电化学沉积Ni(OH)2纳米粒子,制备相应的复合材料。结构表征显示直径约4 nmα-Ni(OH)2纳米粒子嵌入石墨烯中空球框架上。电容性能研究显示,三维结构多孔石墨烯中空球/氢氧化镍复合材料(PHGSN12)在5 m V s-1扫速下,可获得2815 F g-1的比电容(基于Ni(OH)2质量)或1319 F g-1(基于电极总质量),即便是增大扫描速率至200 m V s-1,比电容仍达到1950 F g-1(基于Ni(OH)2质量),其保持率为70%左右。该复合材料高比电容和优异倍率性能的获得归因于粒径小的Ni(OH)2纳米粒子、便于离子扩散和迁移的三维多孔中空结构以及利于电子快速传递RGO基底材料。(3)以Si O2球作为模板,氨基化后共价或物理吸附氧化石墨烯(Si O2@GO),将得到的Si O2@GO与二苄基二硫醚(BDS)一起直接煅烧,再经氢氟酸溶液刻蚀Si O2,制备出硫掺杂三维多孔石墨烯中空球(S-PGHS)。X射线光电子能谱和拉曼光谱证实硫原子以共价键方式被引入到三维多孔石墨烯中空球。研究结果表明S-PGHS作为燃料电池阴极氧还原反应(ORR)的非金属催化剂具有优异催化活性,其催化ORR过程的电子转移数为4,且耐甲醇性和稳定性超过目前商用的电催化材料Pt/C(40 wt%)。同时,对比研究了硫掺杂前后三维多孔RGO中空球以及硫掺杂普通RGO的电化学电容性能。结果显示,三维结构硫掺杂RGO中空球(S-PGHS-900)表现出高的比电容(2 m V s-1的扫速下为236 F g-1和0.2 A g-1的电流密度下放电为343 F g-1),优异的倍率性能(扫速增大的500 m V s-1电容仍保持到120 F g-1)以及良好的循环稳定性(循环1000次仅损失4%),其电容性能远优于未掺杂硫或硫掺杂的普通RGO。这些结果显示增加电活性的硫掺杂以及便于离子扩散和电子传递的三维结构可协同提高ORR催化和电容性能。(4)分别以GO和纳米Si O2为形貌和介孔模板、原位聚合的聚吡咯作为碳源、KOH为活化造孔剂构建三明治型分级多孔结构杂化碳纳米片。结构表征结果显示该杂化碳片具有高比表面积(1588 m2 g-1)、大孔容(1.1 cm3 g-1)以及丰富的微介孔(0.8-6.0 nm),其厚度为10-25 nm。以该纳米碳片装载高达74 wt%纳米硫,并应用于锂硫电池正极而表现出优异电化学性能,包括高可逆容量(0.5C倍率下放电容量为1370 m Ah g-1),优异倍率性能(10C倍率下放电容量为510 m Ah g-1)以及良好循环稳定性(1C倍率下循环100次后容量仍可达860 m Ah g-1)。这结果表明丰富微介孔、大孔容和高比表面积以及石墨烯基三明治型的薄碳纳米片有效固定多硫化物,便于电子传递,从而改善锂硫二次电池性能。
[Abstract]:The development of high performance of the "green" electrochemical energy device is an effective solution to the human facing the "energy crisis" and "environmental pollution" of the two problems in an important way, and the electrode material is one of the key factors affecting the electrochemical performance of the device. Therefore, the design and synthesis of electrode materials with excellent performance will have important significance and academic value. In recent years, graphene due to its excellent mechanical properties and electrical conductivity and high specific surface area, the graphene and graphene based nano materials used in electrochemical energy of concern, such as the super capacitor, the field of lithium batteries and fuel cells. However, the use of graphene oxide (GO) prepared by reduction of graphite oxide graphene (RGO) process of synthesis of alkenyl or macroscopic graphite composite materials in RGO is easy to agglomerate, which leads to the specific surface area is far lower than the theoretical value, the active site and reduce power For electrically active material of electron transfer and charge transfer and diffusion of electrolyte were divided, the electrochemical properties of graphene or graphene based composite materials did not reach the expected effect. Enhance the build three-dimensional structure of graphene or graphene based nano materials will effectively improve the utilization rate of the graphene surface, increased electrical activity sites accelerate the electron transfer, easy electrolyte permeation and ion transport, which is expected to improve the electrochemical performance of graphene nano materials. Therefore, this paper presents the design and synthesis of several kinds of graphene based three-dimensional structure of nano materials, research in the application of super capacitors, fuel cell cathode and lithium sulfur battery two times in the relationship to explore the structure and properties. The main research contents and innovations are as follows: (1) by hydrothermal reduction of graphene oxide / carbon nanotubes / nickel hydroxide (RGO/CNTs/Ni (OH) 2) three yuan composite material Material. The characterization results show that 5-10 nm alpha -Ni (OH) RGO/CNTs complex 2 particles embedded within the three-dimensional structure of the formation of the corresponding composites (GC2N2). The study shows that the electrode material GC2N2 exhibited high specific capacitance, excellent rate capability and cycle stability. In addition, GC2N2 and RGO/ CNTs (P GC) porous materials assembled the asymmetric capacitor, the capacitance of 75 F g-1 (20 A g-1 current density discharge), energy density and power density were 30.1 Wh kg-1 and 17 K W kg-1. capacitor performance and cycle stability increase is mainly attributed to the carbon nanotube into three-dimensional conductive network structure formed between the graphene sheets, is conducive to the electrolyte penetration and diffusion, but also conducive to the charge transfer and electron transfer, and effectively prevent the agglomeration of active substances and relieve the volume expansion and contraction. (2) using the template method to prepare three-dimensional structure of graphene hollow ball Kong Shi framework, And the electrochemical deposition of Ni in the framework of the material (OH) 2 nanoparticles, preparation of composite materials. The corresponding characterization showed a diameter of about 4 nm alpha -Ni (OH) 2 nanoparticles embedded graphene hollow sphere frame. The research on the capacitance performance shows that the three-dimensional structure of porous hollow graphene ball / nickel hydroxide composite (PHGSN12 5 m V s-1) at the scan rate, can obtain 2815 F g-1 specific capacitance (based on Ni (OH) 2) or 1319 F g-1 (based on the total mass, even the electrode) increasing scan rate to 200 m V s-1, the specific capacitance still reached 1950 F g-1 (based on Ni (OH) 2 the amount of the retention rate was 70%), respectively. The composite material with high specific capacitance and excellent rate performance was attributed to the small particle size of Ni (OH) 2 nanoparticles, three-dimensional porous hollow structure for ion diffusion and migration as well as conducive to the rapid transfer of RGO substrate material. (3) to Si electronic O2 spheres as template, amino after physical or covalent The adsorption of graphene oxide (Si O2@GO), the Si O2@GO two and two benzyl sulfide (BDS) with direct calcination, followed by hydrofluoric acid etching of Si O2, preparation of sulfur doped porous graphene hollow spheres (S-PGHS) and.X ray photoelectron spectroscopy and Raman spectra of sulfur by covalent bond atoms the way is introduced into three-dimensional porous graphene hollow spheres. The results show that S-PGHS as the cathode oxygen reduction reaction (ORR) of the non metal catalyst has excellent catalytic activity and the catalytic process of ORR electron transfer number is 4, and the methanol resistance and stability than the current commercial electric catalytic materials Pt/C (40 wt%). At the same time, a comparative study of the sulfur doped and three-dimensional porous RGO hollow spheres and sulfur doped RGO electrochemical capacitance performance. The results show that the three-dimensional structure of sulfur doped RGO hollow spheres (S-PGHS-900) exhibit a high specific capacitance (scan rate of 2 m s-1 to 2 V The current density of 36 F g-1 and 0.2 A g-1 343 F g-1) discharge, excellent rate capability (500 m V S-1 capacitor sweep speed remains increased to 120 F g-1) and good cycling stability (1000 cycles, the capacitance loss of only 4%) performance is far better than the undoped sulfur or sulfur doping the ordinary RGO. these results show that the three-dimensional structure of sulfur doped increased electrical activity and to facilitate the ion diffusion and electron transfer can enhance catalytic ORR and capacitance performance. (4) respectively by GO and Si O2 nano morphology and mesoporous template in situ polymerization of polypyrrole as a carbon source, the activation of KOH pore forming agent sandwich construction hierarchical porous structure of hybrid carbon nanosheets. The characterization results show that the hybrid carbon film with high surface area (1588 M2 g-1), large pore volume (1.1 cm3 g-1) and rich micro mesoporous (0.8-6.0 nm), the thickness of 10-25 nm. to the carbon nano sheet loading up to 74 wt% Nano sulfur, and applied to the cathode of lithium sulfur batteries and exhibit excellent electrochemical properties, including high reversible capacity (0.5C rate discharge capacity of 1370 m Ah g-1), excellent rate performance (10C rate discharge capacity of 510 m Ah g-1) and good cycling stability (100 times the capacity is still up 860 m Ah g-1 circulating 1C rate). This result shows that the rich micro mesoporous thin carbon nanosheets effectively fixed polysulfide large pore volume and high surface area of graphene based sandwich type, facilitate electron transfer, so as to improve the performance of lithium sulfur battery two times.

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1

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