低热导率复合材料结构设计与热电性能研究

发布时间：2018-08-17 17:05

【摘要】：近年来,随着能源危机和环境污染两大问题的日益严重,绿色能源的开发与利用越来越受到人们的重视。热电材料是一种利用热电技术实现电能与热能相互转换的环境友好型能源材料,广泛应用于温差发电和热电制冷领域。通常用ZT值(ZT=S2σT/k)来评价材料的热电性能,由公式可知除温度T外,热电性能还与Seebeck系数S、电导率σ和热导率k三个热电参数有关,其中,降低材料的热导率k是优化热电性能的有效途径之一。因此,如何构筑低热导率热电材料,改善热电性能的研究具有非常重要的意义。本文从选用特殊材料、构筑特殊结构、掺杂纳米粒子等方法出发,设计制备低热导率热电复合材料。具体研究内容和结论如下:(1)选用导电高分子聚(3,4-二氧乙撑噻吩):聚对苯乙烯磺酸(PEDOT:PSS)为原料,引入多壁碳纳米管(MWCNTs)和Ag纳米片,通过设计特殊结构来制备低热导率热电材料。研究发现该材料具有三维网络结构,其中MWCNTs构筑孔洞结构,比表面积可达228m2/g。在Ag掺杂PEDOT:PSS/MWCNT(PCA)复合气凝胶中,引入Ag纳米片对热导率影响较小,PCA气凝胶热导率变化范围在0.06 W/mK~0.11 W/mK之间,与纯的PEDOT:PSS(0.348±0.01 W/mK)相比,热导率几乎降低了一个数量级。此外,Ag纳米片的添加有利于同时提高复合材料电导率和Seebeck系数。综合三个因素的影响,制备的热电材料室温下PCA气凝胶ZT值最高为7.56×10-3。(2)选用高Seebeck系数、高电导率的无机纳米材料Bi_2Te_3与PEDOT:PSS复合制备PEDOT:PSS/Bi_2Te_3(PB)复合气凝胶,并对热电性能进行了测试和分析。通过SEM表征发现纯PEDOT:PSS气凝胶内部孔洞结构清晰且完整,在PB复合气凝胶中Bi_2Te_3粉体均匀的分散在高分子基体中,而且孔洞结构没有被破坏。室温下,PB复合气凝胶热导率在0.15 W/mK~0.24 W/mK之间并随着Bi_2Te_3含量的增加而增大。引入Bi_2Te_3导致复合气凝胶电导率提高,Seebeck系数最大高达92.61μV/K。(3)以低导热材料滤纸为基底,采用物理旋涂方法制PEDOT:PSS/MWCNTs(PMF)纳米复合薄膜热电材料。实验研究了原料比例、涂层数目及测试温度对复合材料热电性能的影响。研究发现MWCNTs在PEDOT:PSS中分散均匀且有良好的界面作用;室温条件下,PMF复合材料热导率较低,热导率最高约为0.2 W/mK左右;原料配比为1:1时,PMF薄膜整体导电性能最佳;随着涂布层数的增加,电导率先增加后降低,当原料配比1:1的PMF样品在涂层数目为3层时,电导率可高达3530.47 S/m,Seebeck系数为15μV/K到19μV/K。(4)采用水热法合成碲化铋粉体,将炭黑(CB)与其掺杂制备不同比例的碲化铋-炭黑(Bi_2Te_3/CB)复合材料,研究了复合材料的热电性能。同时采用TGA、SEM、XRD等分析方法表征复合材料的结构,探究了微观结构与热电性能的关系。研究发现:室温下,CB的引入使复合材料的热导率大大降低(从0.59 W/mK降到0.09 W/mK);随着Bi_2Te_3含量的增加,复合材料的电导率、热导率均增大,Seebeck系数先增加后降低;当Bi_2Te_3含量为88.9 wt%时,在558℃下烧结10 min复合材料室温下的ZT值最大(ZT=0.21)。
[Abstract]:In recent years, with the energy crisis and environmental pollution becoming more and more serious, people pay more and more attention to the development and utilization of green energy. ZT=S2T/k) is used to evaluate the thermoelectric properties of materials. The formula shows that besides temperature T, the thermoelectric properties are also related to Seebeck coefficient S, conductivity_and thermal conductivity K. Reducing the thermal conductivity K of materials is one of the effective ways to optimize the thermoelectric properties. Therefore, how to construct low thermal conductivity thermoelectric materials and improve the thermoelectric properties are studied. In this paper, low thermal conductivity thermoelectric composites are designed and fabricated by selecting special materials, constructing special structures and doping nanoparticles. The specific research contents and conclusions are as follows: (1) Poly (3,4-dioxoethylene thiophene): poly (p-styrene sulfonic acid) (PEDOT: PSS) is selected as raw material to introduce multi-walled carbon nanoparticles. Low thermal conductivity thermoelectric materials were prepared by designing special structures of nanotubes (MWCNTs) and Ag nanosheets. It was found that the materials had three-dimensional network structure, in which MWCNTs had a pore structure with a specific surface area of 228 m2/g. In Ag-doped PEDOT: PSS / MWCNT (PCA) composite aerogels, the introduction of Ag nanosheets had little effect on the thermal conductivity, and the thermal conductivity of PCA aerogels was less affected. The thermal conductivity of PCA aerogels was almost one order of magnitude lower than that of pure PEDOT:PSS (0.348.01 W/mK). In addition, the addition of Ag nanosheets was beneficial to simultaneously improve the conductivity and Seebeck coefficient of the composites. PEDOT:PSS/Bi_2Te_3(PB) composite aerogel was prepared by using high Seebeck coefficient and high conductivity inorganic nano-material Bi_2Te_3 and PEDOT:PSS. The thermoelectric properties of the composite aerogel were tested and analyzed. The pore structure of pure PEDOT:PSS aerogel was clear and complete by SEM. At room temperature, the thermal conductivity of PB composite aerogel increases with the increase of Bi_2Te_3 content. The introduction of Bi_2Te_3 results in the increase of the conductivity of the composite aerogel, and the Seebeck coefficient is up to 92.61 mu V/K. PEDOT: PSS / MWCNTs (PMF) nanocomposites were prepared by physical spin-coating method. The effects of the ratio of raw materials, the number of coatings and the testing temperature on the thermoelectric properties of the composites were investigated experimentally. The highest conductivity is about 0.2 W/mK; when the ratio of raw materials is 1:1, the overall conductivity of PMF film is the best; with the increase of coating layers, the conductivity increases first and then decreases; when the ratio of raw materials is 1:1, the conductivity of PMF sample is as high as 3530.47 S/m, Seebeck coefficient is 15 to 19 uV/K. (4) Bismuth telluride is synthesized by hydrothermal method. Bi_2Te_3/CB composites were prepared by doping carbon black (CB) with CB. The thermoelectric properties of the composites were studied. The structure of the composites was characterized by TGA, SEM, XRD, and the relationship between microstructure and thermoelectric properties was investigated. The conductivity decreases greatly (from 0.59 W/mK to 0.09 W/mK); with the increase of Bi_2Te_3 content, the conductivity and thermal conductivity of the composites increase, and the Seebeck coefficient increases first and then decreases; when the content of Bi_2Te_3 is 88.9 wt%, the ZT value of the composites sintered at 558 for 10 minutes is the highest (ZT = 0.21).
【学位授予单位】：四川师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33

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