石墨烯基高密度碳材料的制備及其超級電容性能研究
發(fā)布時間：2019-02-18 08:16
【摘要】：石墨烯是一種獨特的具有單層碳原子結(jié)構(gòu)的二維碳材料,它的理論比表面積高達2630 m2 g-1,因此被認(rèn)為是一種理想的超級電容器電極材料。然而在實際制備的過程中,由于宏觀的石墨烯材料中片層狀結(jié)構(gòu)間的無序搭接,使其表現(xiàn)出較低的表觀密度值,這嚴(yán)重限制了石墨烯基超級電容電極的體積能量密度,同時石墨烯片層間再堆疊現(xiàn)象的發(fā)生也降低了材料的可利用比表面積。因此,對石墨烯材料的結(jié)構(gòu)設(shè)計、界面組裝以及孔結(jié)構(gòu)調(diào)控是獲得高密度多孔碳電極材料的關(guān)鍵因素。本文利用氧化石墨烯表面含氧官能團與電解質(zhì)離子的相互作用制備出幾種具有高體積能量密度的石墨烯基碳材料,并對材料的物理性質(zhì)、電化學(xué)性能進行了詳細(xì)的表征。對人造石墨和天然石墨兩種不同原料制備的氧化石墨烯進行了KOH活化造孔處理,通過分析發(fā)現(xiàn)石墨原料的結(jié)晶度對石墨烯片層的活化效果有非常重要的影響,采用人造石墨和天然石墨兩種原料在堿碳比5:1的條件下獲得的活化石墨烯材料的比表面積分別可達2193 m2 g-1和1265 m2 g-1,然而由于石墨烯材料活化過程需要較高的堿碳比,因此活化石墨烯具有非常低的收率。本文通過鈉離子的靜電搭接作用,將氧化石墨烯片層與海藻酸鈉分子進行微觀結(jié)構(gòu)層面的搭接,所形成的前驅(qū)物經(jīng)過后續(xù)碳化和活化過程后可獲得活性炭顆粒均勻、緊密附著在石墨烯片層上的三維多孔石墨烯基復(fù)合材料,該材料的比表面積高達2979 m2 g-1。三維多孔石墨烯基復(fù)合材料在離子液體1-乙基-3-甲基咪唑啉雙(三氟甲基磺�；�)亞胺(EMIM TFSI)中的比電容值為175 F g-1,對應(yīng)的能量密度可達74.4 Wh kg-1,同時該復(fù)合材料的壓實密度優(yōu)于活化石墨烯材料,其在離子液體中的體積能量密度可以達到30.5 Wh L-1,該數(shù)值明顯高于文獻中報道的活化石墨烯材料(23 Wh L-1)。為了進一步提高石墨烯基材料的密度值,采用KOH溶液作為還原媒介還原氧化石墨烯,通過鉀離子與氧化石墨烯片層上的含氧官能團的相互作用,可以使還原氧化石墨烯的片層間發(fā)生定向的面-面排布,形成高度有序的致密層狀微觀結(jié)構(gòu)。在還原的過程中鉀離子可以抑制石墨烯片層間發(fā)生不可逆復(fù)合,從而使得石墨烯層間形成大量的孔徑在0.4 nm以下的超微孔結(jié)構(gòu),這種致密層狀的微孔結(jié)構(gòu)既實現(xiàn)了高達1.58 g cm-3的壓實密度,還通過豐富的微孔表面提供了高的雙電層電容和法拉第贗電容。電化學(xué)測試表明,這種高密度石墨烯在水系電解液中的體積比電容值高達508 F cm-3,在水系電解液中其體積能量密度高達30 Wh L-1。此外,采用簡單的硫酸鈉溶液預(yù)處理氧化石墨烯,通過鈉離子對氧化石墨烯片層間的預(yù)插層作用,降低了熱還原過程中氧化石墨烯片層間之間的氣體膨脹壓力,這種熱膨脹石墨烯材料相對未經(jīng)過預(yù)處理的材料具有更高的微孔比例,因而具有更高的密度,體積能量密度可以達到26 Wh L-1。自支撐石墨烯膜可以避免導(dǎo)電劑和粘結(jié)劑的使用,從而進一步提高器件的整體體積能量密度,本文將氧化石墨烯懸浮液進行濃縮后,進行刮涂處理,干燥后可以獲得力學(xué)強度良好的氧化石墨烯薄膜,該薄膜在蒸餾水中進行水熱還原時很難保持薄膜的完整性,通過向蒸餾水中引入電解質(zhì)KOH、Na2SO4或H2SO4時,可以獲得具有完整性和柔韌性的自支撐石墨烯薄膜,這一現(xiàn)象的內(nèi)在機制可能是石墨烯片層間π-π引力與靜電作用相互平衡的結(jié)果。使用雙氧水對氧化石墨烯進行造孔處理后獲得了面內(nèi)多孔氧化石墨烯薄膜,這種薄膜在硫酸溶液中進行水熱還原處理后,獲得了密度值為1.14 g cm-3的自支撐多孔石墨烯薄膜材料,該材料在0.1 A g-1電流密度下的質(zhì)量比電容值和體積比電容值分別為179 F g-1和204 F cm-3,同時還表現(xiàn)出優(yōu)異的倍率性能。
[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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ127.11;TM53
，
本文編號：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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ127.11;TM53
，
本文編號：2425660
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