K. Kawata, T. Oya
Graduate School of Engineering, Yokohama National University,
Keywords: carbon-nanotube(CNT), CNT-composite paper, thermoelectric power generating paper, Seebeck effect
Summary:We propose an unique thermoelectric material based on a carbon-nanotube(CNT)-composite paper that a composite material of the CNT and a paper, i.e., a “thermoelectric power generating paper.” In recent years, about two thirds of the consumed energy is wasted as heat. As a candidate of solutions for this problem, heat recovery and power regeneration technologies have been focused. For instance, various thermoelectric materials that enable heat recovery and power regeneration efficiently have been developed by the technologies. Recently, it has been found that the CNTs show a giant Seebeck effect, i.e., the CNT can also be the thermoelectric material. However, it is difficult to use the CNT as the thermoelectric material generally because its size is nanoscale. Here, we propose the use of our CNT-composite paper for new thermoelectric material using the CNTs. The composite paper can be fabricated easily by the papermaking method based on the traditional Japanese washi paper making process. In concrete, the CNT dispersion and a pulp (paper material) dispersion are prepared firstly. Then, they are mixed and poured into a tray. After that, the pulp fibers with the CNTs are scooped up by using a fine net. Finally, the scooped materials are dried to finalize the papermaking process. Our CNT-composite paper shows almost all functions of the CNT despite of the paper. To generate power by using the thermoelectric material, there are some important points. As the first point, the material has temperature difference in it. In addition, the difference should be kept. Therefore, thermal conductivity of the material should be low. In contrast, electrical conductivity of the power generating materials should be high, i.e., the thermoelectric materials should manage both low thermal and high electrical conductivities. Our CNT-composite paper is expected to realize the above request. Originally, the CNTs have the high thermal- and high electrical-conductivities. However, our composite paper has also pulp fibers that have a thermal insulation property. As the next point, a metallic or a semiconducting material should be chosen to obtain the Seebeck effect. Our composite paper can show the metallic and the semiconducting properties because the contained CNT has them. Therefore, our paper is expected to be suitable materials. Here, we tested the thermoelectric power generating ability of our CNT-composite paper. First we provide the temperature difference for both metallic and semiconducting CNT-composite papers, respectively. As results, the Seebeck effect was observed from both papers. Especially, a giant Seebeck effect was observed from the semiconducting paper. Therefore, our CNT-composite paper can be used as the thermoelectric power generating material. Now, we are testing the power generating ability of the p-type and n-type semiconducting CNT-composite papers, respectively. Moreover, we are also testing the ability of the combined sample that connects the p-type and the n-type papers. References  T. Oya and T. Ogino, Carbon 46, 169, 2008.  Y. Nakai, et al., Appl. Phys. Expr. 7, no2, 1, 2014.