竹纳米纤维素及其功能材料的制备与电化学性能研究

发布时间：2018-06-23 22:00

本文选题：竹纤维素 + 碳纳米纤维　；参考：《青岛大学》2017年硕士论文

【摘要】：碳纳米纤维(carbon nanofiber,CNF)是指尺寸为纳米尺度的碳纤维,具有低密度、低缺陷、高孔隙率、高比表面积以及良好的力学性能和优异的导电性能等特点。因此,CNF在电气设备,可充电电池和超级电容器的电极材料以及化学传感器等许多领域都展现出巨大的潜力。然而,CNF的合成主要依靠合成聚合物,如:聚丙烯腈,聚酰亚胺和聚乙烯醇的热解来获得。随着化石能源日渐耗尽和全球气候变暖,这种合成方式越来越难以满足人们对高性能、环境友好型材料的需求。以细菌纤维素为代表的可控生物质材料是替代合成聚合物的备选方案,但是利用生物法制备细菌纤维素的工艺复杂,耗时长且成本高,限制了其工业化生产和应用。本论文以漂白的竹浆为原料,通过简易可控的机械法处理得到不同尺寸分布的纤维素纳米纤丝,然后通过高温热解处理得到高比表面积的多孔纳米碳材料。以锌空气电池、锂离子电池为研究对象研究了碳纳米纤维的电化学性能。围绕这个目标,本文开展了以下几个方面的研宄工作。(1)利用机械法和TEMPO氧化的方法得到形貌均一且超细的竹浆纤维纳米带(ultrathin nanometer cellulose nanoribbons,Cel-NRs),通过氨气(NH3)氛围下高温热解制备氮掺杂的碳纳米带(N-doped carbon nanoribbons,CNRs)。在此结构中,TEMPO的选择性氧化使竹纤维容易进行后续的加工处理且不会改变竹纤维原有的晶型,氮原子的引入提高了CNRs表面的活性位点,克服了CNRs单独作为催化剂催化氧还原反应(oxygen reduction reaction,ORR)和锌空气电池氧电极催化剂材料时的缺点。N-CNRs高密度氮掺杂的活性位点(10.6 at%)和超薄纳米结构使其具有良好的ORR催化活性,其起始电位、半波电位和电子转移数都可以与商业化Pt/C催化剂相媲美,其抗甲醇性和稳定性都优于商业化Pt/C催化剂。N-CNRs作为锌空气电池氧电极催化剂材料具有高比容量(在电流密度为20 mA/g时比容量为590 mAhgZn-1)和优异的循环稳定性。(2)利用机械法制备了结构可控的竹浆纳米纤维,冷冻干燥制备出具有3D结构的纳米纤维素气凝胶,通过NH3氛围下的高温热解和氢氧化钾(KOH)活化制备了N-ACNF。其拥有高比表面积、高导电性、部分石墨化和分层级多孔结构等特点。这种优异的结构使其作为储能材料时具有快的电子传输速率和有效的电解液扩散等优势,可作为高效多能的能源材料应用于锂离子电池中。竹纤维的直径控制在~50 nm时制备的样品(N-ACNF-50)拥有最好的电化学性能。作为锂离子电池负极材料时,N-ACNFs-50具有高比容量、优秀的循环稳定性和倍率性能。其在电流密度1 A/g下连续充放电100次以后比容量达到630.7 mAh/g,在电流密度高达20 A/g下,比容量还能维持在289 mAh/g。
[Abstract]:Carbon nanofiber (carbon nanofiber) is a kind of carbon fiber with low density, low defect, high porosity, high specific surface area, good mechanical properties and excellent electrical conductivity. So CNF has great potential in many fields, such as electrical equipment, rechargeable battery and supercapacitor electrode materials, chemical sensors and so on. However, the synthesis of CNF mainly depends on the pyrolysis of polyacrylonitrile, polyimide and polyvinyl alcohol. With the depletion of fossil energy and global warming, it is becoming increasingly difficult to meet the demand for high-performance, environmentally friendly materials. The controllable biomass material, represented by bacterial cellulose, is an alternative to synthetic polymer. However, the process of preparing bacterial cellulose by biological method is complex, time-consuming and costly, which limits its industrial production and application. In this paper, bleached bamboo pulp was used as raw material, cellulose nanofilament with different size distribution was obtained by simple and controllable mechanical treatment, and porous nano-carbon material with high specific surface area was obtained by pyrolysis at high temperature. The electrochemical properties of carbon nanofibers were studied by zinc air battery and lithium ion battery. Around this goal, In this paper, the following studies have been carried out. (1) homogeneous and ultrafine bamboo fiber nanowires (ultrathin nanometer cellulose nanoribbonsCel-NRs) were prepared by mechanical method and tempo oxidation. N-doped carbon nanoribbonsNRs were prepared by pyrolysis at high temperature in ammonia gas (NH3). In this structure, the selective oxidation of TEMPO makes the bamboo fiber easy to be processed after processing and does not change the original crystal form of bamboo fiber. The introduction of nitrogen atom enhances the active site of CNRs surface. It overcomes the shortcomings of CNRs as catalyst for oxygen reduction reaction (oxygen reduction reactionorr) and zinc air battery oxygen electrode catalyst materials. The high density nitrogen-doped active sites (10.6 at%) and ultrathin nanostructures of CNRs make them have good ORR catalytic activity. Its initial potential, half-wave potential and electron transfer number are comparable to commercial Pt / C catalysts. The methanol resistance and stability of the catalyst are better than that of commercial PTR / C catalyst. N-CNRs have high specific capacity (590mAhgZn-1 at 20 mA/g current density) and excellent cycling stability. (2) the catalyst material for zinc air battery has high specific capacity (590mAhgZn-1 at current density of 20 mA/g) and excellent cycling stability. Bamboo pulp nanofibers with controllable structure were prepared by mechanical method. Nano-cellulose aerogels with 3D structure were prepared by freeze-drying. N-ACNF was prepared by pyrolysis at high temperature and activation of potassium hydroxide (Koh) in NH _ 3 atmosphere. It has high specific surface area, high conductivity, partial graphitization and hierarchical porous structure. Because of its excellent structure, it has the advantages of fast electron transfer rate and effective electrolyte diffusion when it is used as energy storage material. It can be used in lithium ion batteries as a high efficiency and multi-energy material. The sample (N-ACNF-50) prepared by controlling the diameter of bamboo fiber at 50 nm has the best electrochemical performance. As a cathode material for lithium ion batteries, N-ACNFs-50 has high specific capacity, excellent cycling stability and rate performance. At current density of 1 / g, the specific capacity is 630.7 mAh/ g, and at the current density of 20 A / g, the specific capacity can be maintained at 289mAh/ g.
【学位授予单位】：青岛大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ352.79;TB34

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