石墨烯基高密度碳材料的制备及其超级电容性能研究
发布时间：2019-02-18 08:16
【摘要】：石墨烯是一种独特的具有单层碳原子结构的二维碳材料,它的理论比表面积高达2630 m2 g-1,因此被认为是一种理想的超级电容器电极材料。然而在实际制备的过程中,由于宏观的石墨烯材料中片层状结构间的无序搭接,使其表现出较低的表观密度值,这严重限制了石墨烯基超级电容电极的体积能量密度,同时石墨烯片层间再堆叠现象的发生也降低了材料的可利用比表面积。因此,对石墨烯材料的结构设计、界面组装以及孔结构调控是获得高密度多孔碳电极材料的关键因素。本文利用氧化石墨烯表面含氧官能团与电解质离子的相互作用制备出几种具有高体积能量密度的石墨烯基碳材料,并对材料的物理性质、电化学性能进行了详细的表征。对人造石墨和天然石墨两种不同原料制备的氧化石墨烯进行了KOH活化造孔处理,通过分析发现石墨原料的结晶度对石墨烯片层的活化效果有非常重要的影响,采用人造石墨和天然石墨两种原料在碱碳比5:1的条件下获得的活化石墨烯材料的比表面积分别可达2193 m2 g-1和1265 m2 g-1,然而由于石墨烯材料活化过程需要较高的碱碳比,因此活化石墨烯具有非常低的收率。本文通过钠离子的静电搭接作用,将氧化石墨烯片层与海藻酸钠分子进行微观结构层面的搭接,所形成的前驱物经过后续碳化和活化过程后可获得活性炭颗粒均匀、紧密附着在石墨烯片层上的三维多孔石墨烯基复合材料,该材料的比表面积高达2979 m2 g-1。三维多孔石墨烯基复合材料在离子液体1-乙基-3-甲基咪唑啉双(三氟甲基磺酰基)亚胺(EMIM TFSI)中的比电容值为175 F g-1,对应的能量密度可达74.4 Wh kg-1,同时该复合材料的压实密度优于活化石墨烯材料,其在离子液体中的体积能量密度可以达到30.5 Wh L-1,该数值明显高于文献中报道的活化石墨烯材料(23 Wh L-1)。为了进一步提高石墨烯基材料的密度值,采用KOH溶液作为还原媒介还原氧化石墨烯,通过钾离子与氧化石墨烯片层上的含氧官能团的相互作用,可以使还原氧化石墨烯的片层间发生定向的面-面排布,形成高度有序的致密层状微观结构。在还原的过程中钾离子可以抑制石墨烯片层间发生不可逆复合,从而使得石墨烯层间形成大量的孔径在0.4 nm以下的超微孔结构,这种致密层状的微孔结构既实现了高达1.58 g cm-3的压实密度,还通过丰富的微孔表面提供了高的双电层电容和法拉第赝电容。电化学测试表明,这种高密度石墨烯在水系电解液中的体积比电容值高达508 F cm-3,在水系电解液中其体积能量密度高达30 Wh L-1。此外,采用简单的硫酸钠溶液预处理氧化石墨烯,通过钠离子对氧化石墨烯片层间的预插层作用,降低了热还原过程中氧化石墨烯片层间之间的气体膨胀压力,这种热膨胀石墨烯材料相对未经过预处理的材料具有更高的微孔比例,因而具有更高的密度,体积能量密度可以达到26 Wh L-1。自支撑石墨烯膜可以避免导电剂和粘结剂的使用,从而进一步提高器件的整体体积能量密度,本文将氧化石墨烯悬浮液进行浓缩后,进行刮涂处理,干燥后可以获得力学强度良好的氧化石墨烯薄膜,该薄膜在蒸馏水中进行水热还原时很难保持薄膜的完整性,通过向蒸馏水中引入电解质KOH、Na2SO4或H2SO4时,可以获得具有完整性和柔韧性的自支撑石墨烯薄膜,这一现象的内在机制可能是石墨烯片层间π-π引力与静电作用相互平衡的结果。使用双氧水对氧化石墨烯进行造孔处理后获得了面内多孔氧化石墨烯薄膜,这种薄膜在硫酸溶液中进行水热还原处理后,获得了密度值为1.14 g cm-3的自支撑多孔石墨烯薄膜材料,该材料在0.1 A g-1电流密度下的质量比电容值和体积比电容值分别为179 F g-1和204 F cm-3,同时还表现出优异的倍率性能。
[Abstract]:Graphene is a unique two-dimensional carbon material with a single-layer carbon atom structure, which has a theoretical specific surface area of 2630 m2 g-1, and is therefore considered to be an ideal super-capacitor electrode material. in the actual preparation process, however, due to the disorder overlap between the sheet-like structures in the macroscopic graphene material, it shows a lower apparent density value, which severely limits the volumetric energy density of the graphene-based super-capacitor electrode, At the same time, the occurrence of the re-stacking of the graphene sheets also reduces the available specific surface area of the material. Therefore, the structural design, interface assembly and pore structure regulation of the graphene material are the key factors to obtain the high-density porous carbon electrode material. In this paper, several graphene-based carbon materials with high volume energy density are prepared by the interaction of the oxygen-containing functional groups and the electrolyte ions on the surface of the graphene oxide, and the physical properties and the electrochemical properties of the materials are characterized in detail. The oxidation graphene prepared from the two different raw materials of the artificial graphite and the natural graphite is subjected to the KOH-activated pore-forming treatment, and the influence of the crystallinity of the graphite raw material on the activation effect of the graphene sheet is found through the analysis, The specific surface area of the activated graphene material obtained under the condition of alkali-to-carbon ratio of 5: 1 by adopting the artificial graphite and the natural graphite can reach the specific surface area of 2193 m2 g-1 and 1265 m2 g-1, respectively, but the activated graphene has a very low yield due to the high alkali-to-carbon ratio during the activation process of the graphene material. In the method, the graphene sheet layer and the sodium alginate molecule are overlapped at the micro-structure level through the electrostatic bonding of the sodium ions, and the formed precursor can obtain the uniform of the active carbon particles after the subsequent carbonization and activation process, The three-dimensional porous graphene-based composite material which is closely attached to the graphene sheet layer has a specific surface area of 2979m2 g-1. The specific capacitance of the three-dimensional porous graphene-based composite material in the ionic liquid 1-ethyl-3-medetomidine bis (trifluoromethylsulfonyl) imine (EMIM TFSI) is 175 F g-1, and the corresponding energy density can reach 74.4Wh kg-1, At the same time, the compaction density of the composite material is superior to that of the activated graphene material, and the volume energy density in the ionic liquid can reach 30. 5Wh L-1, which is obviously higher than that of the activated graphene material reported in the literature (23 Wh L-1). in order to further improve the density value of the graphene-based material, the KOH solution is used as a reduction medium to reduce the graphene oxide, a highly ordered dense layered microstructure is formed. in the reduction process, the potassium ion can inhibit the irreversible recombination between the graphene sheets, so that a large number of super-micro-pore structures with a pore size below 0.4 nm are formed between the graphene layers, a high double electrical layer capacitance and a faraday pseudo-capacitance are also provided by a rich micro-porous surface. The electrochemical tests show that the volume of the high-density graphene in the water-based electrolyte reaches 508 F-3, and the volume energy density of the high-density graphene is up to 30Wh L-1 in the water-based electrolyte. in addition, the graphene is pretreated by adopting a simple sodium sulfate solution, the pre-insertion layer between the graphene oxide sheets is influenced by the sodium ion, and the gas expansion pressure between the graphene oxide sheets in the thermal reduction process is reduced, This thermal expansion graphene material has a higher micropore ratio with respect to the material that is not pretreated, and thus has a higher density, and the bulk energy density can reach 26 Wh L-1. The self-supporting graphene film can avoid the use of the conductive agent and the adhesive, thereby further improving the overall volume energy density of the device, The film is difficult to maintain the integrity of the film when the film is subjected to hydrothermal reduction in distilled water, and a self-supporting graphene film with integrity and flexibility can be obtained by introducing the electrolyte KOH, Na2SO4 or H2SO4 into distilled water, The intrinsic mechanism of this phenomenon may be the result of the mutual balance between the gravitational and electrostatic interactions between the graphene sheets. after performing water thermal reduction treatment on the graphene oxide by using the hydrogen peroxide, the self-supporting porous graphene film material with the density value of 1. 14 g cm-3 is obtained after the water thermal reduction treatment is carried out in the sulfuric acid solution, The mass ratio of the material at the current density of 0.1 A g-1 is 179 F g-1 and 204 F cm-3, respectively, than the capacitance value and the volume specific capacitance value, and also exhibits excellent rate performance.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ127.11;TM53
，
本文编号：2425660
[Abstract]:Graphene is a unique two-dimensional carbon material with a single-layer carbon atom structure, which has a theoretical specific surface area of 2630 m2 g-1, and is therefore considered to be an ideal super-capacitor electrode material. in the actual preparation process, however, due to the disorder overlap between the sheet-like structures in the macroscopic graphene material, it shows a lower apparent density value, which severely limits the volumetric energy density of the graphene-based super-capacitor electrode, At the same time, the occurrence of the re-stacking of the graphene sheets also reduces the available specific surface area of the material. Therefore, the structural design, interface assembly and pore structure regulation of the graphene material are the key factors to obtain the high-density porous carbon electrode material. In this paper, several graphene-based carbon materials with high volume energy density are prepared by the interaction of the oxygen-containing functional groups and the electrolyte ions on the surface of the graphene oxide, and the physical properties and the electrochemical properties of the materials are characterized in detail. The oxidation graphene prepared from the two different raw materials of the artificial graphite and the natural graphite is subjected to the KOH-activated pore-forming treatment, and the influence of the crystallinity of the graphite raw material on the activation effect of the graphene sheet is found through the analysis, The specific surface area of the activated graphene material obtained under the condition of alkali-to-carbon ratio of 5: 1 by adopting the artificial graphite and the natural graphite can reach the specific surface area of 2193 m2 g-1 and 1265 m2 g-1, respectively, but the activated graphene has a very low yield due to the high alkali-to-carbon ratio during the activation process of the graphene material. In the method, the graphene sheet layer and the sodium alginate molecule are overlapped at the micro-structure level through the electrostatic bonding of the sodium ions, and the formed precursor can obtain the uniform of the active carbon particles after the subsequent carbonization and activation process, The three-dimensional porous graphene-based composite material which is closely attached to the graphene sheet layer has a specific surface area of 2979m2 g-1. The specific capacitance of the three-dimensional porous graphene-based composite material in the ionic liquid 1-ethyl-3-medetomidine bis (trifluoromethylsulfonyl) imine (EMIM TFSI) is 175 F g-1, and the corresponding energy density can reach 74.4Wh kg-1, At the same time, the compaction density of the composite material is superior to that of the activated graphene material, and the volume energy density in the ionic liquid can reach 30. 5Wh L-1, which is obviously higher than that of the activated graphene material reported in the literature (23 Wh L-1). in order to further improve the density value of the graphene-based material, the KOH solution is used as a reduction medium to reduce the graphene oxide, a highly ordered dense layered microstructure is formed. in the reduction process, the potassium ion can inhibit the irreversible recombination between the graphene sheets, so that a large number of super-micro-pore structures with a pore size below 0.4 nm are formed between the graphene layers, a high double electrical layer capacitance and a faraday pseudo-capacitance are also provided by a rich micro-porous surface. The electrochemical tests show that the volume of the high-density graphene in the water-based electrolyte reaches 508 F-3, and the volume energy density of the high-density graphene is up to 30Wh L-1 in the water-based electrolyte. in addition, the graphene is pretreated by adopting a simple sodium sulfate solution, the pre-insertion layer between the graphene oxide sheets is influenced by the sodium ion, and the gas expansion pressure between the graphene oxide sheets in the thermal reduction process is reduced, This thermal expansion graphene material has a higher micropore ratio with respect to the material that is not pretreated, and thus has a higher density, and the bulk energy density can reach 26 Wh L-1. The self-supporting graphene film can avoid the use of the conductive agent and the adhesive, thereby further improving the overall volume energy density of the device, The film is difficult to maintain the integrity of the film when the film is subjected to hydrothermal reduction in distilled water, and a self-supporting graphene film with integrity and flexibility can be obtained by introducing the electrolyte KOH, Na2SO4 or H2SO4 into distilled water, The intrinsic mechanism of this phenomenon may be the result of the mutual balance between the gravitational and electrostatic interactions between the graphene sheets. after performing water thermal reduction treatment on the graphene oxide by using the hydrogen peroxide, the self-supporting porous graphene film material with the density value of 1. 14 g cm-3 is obtained after the water thermal reduction treatment is carried out in the sulfuric acid solution, The mass ratio of the material at the current density of 0.1 A g-1 is 179 F g-1 and 204 F cm-3, respectively, than the capacitance value and the volume specific capacitance value, and also exhibits excellent rate performance.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ127.11;TM53
，
本文编号：2425660
本文链接：https://www.wllwen.com/kejilunwen/huaxuehuagong/2425660.html
