Website of Takashi Itoh Lab., Dept of Chemical Systems Engineering, Graduate School of Engineering, Nagoya University

Main Research and Features

　 Drastical improvement of the conversion efficiency of heat energy to electric energy by combustion of fossil fuels such as coal, petroleum, natural gas, etc. will be a global urgent task, which greatly contribute to energy conservation and solve the global warming problem by carbon dioxide etc. In order to solve this problem, it is necessary to build systems for improving the efficiency of combustion itself and for converting directly unused low energy of waste heat discharged by combustion into electrical energy and to develop their elemental technologies. In this research group, we focus on thermoelectric materials, which are semiconductors that can convert directly waste heat discharged from various systems into electric energy, and we research on high performance materials and highly efficient thermoelectric power generation system. We are also developing materials that can be used in high temperature environments for energy conversion systems.
　In waste heat generated in various systems, high temperature waste heat (800 ^oC or higher) can be utilized for steam turbines and fuel reforming for fuel cells besides thermoelectric power generation. On the other hand, since the medium-temperature waste heat (from 300 to 600 ^oC) is the waste heat of the main combustion system, and its utilization is almost restricted to thermoelectric generation, developments of high performance thermoelectric materials and of thermoelectric power generation system that has improved conversion efficiency to the utmost is expected. Thus, our research group conducts research by setting research themes as follows.

　Development of various high-performance thermoelectric materials (non-oxide type) suitable for thermoelectric power generation from medium temperature waste heat (from 300 to 600 ^oC) will be carried out and the characteristics that affect performance will be evaluated. Specifically, the materials of Co-Sb type, Zn-Sb type, Ag-Sb-Te type, Mn-Si type and Mg-Si type are synthesized using combination method of mechanical alloying, pulse discharge sintering, and liquid-solid phase reaction, etc. In particular, synthesis is carried out focusing on environmentally symbiotic thermoelectric materials such as Mg₂Si and MnSi_1.73 made of environmentally friendly and abundant raw materials. Furthermore, we try to improve the performance of thermoelectric materials by reducing thermal conductivity based on phonon scattering caused with uniformly dispersing nano-sized substances such as fullerenes and carbon nanotubes in thermoelectric materials.

　In order to achieve high efficiency in thermoelectric power generation, construction of functional gradient thermoelectric materials is one promising method. Because a variety of thermoelectric materials have temperature ranges that exhibit the best thermoelectric performance, improvement of power generation efficiency is expected by the combination of the best thermoelectric materials according to the temperature distribution inside the material and by the large temperature difference between the high temperature end and the low temperature end. In this research, we study the optimization of combinations of dissimilar thermoelectric materials, and observe the interface state between dissimilar thermoelectric materials and evaluate the performance of modularized composite thermoelectric materials.

　We reviewed complicated conventional module manufacturing processes such as cutting out of thermoelectric element, arrenging of p and n elements, and junction with electrodes, packaging, and proposed a novel module manufacturing method suitable for mass production and reduced module manufacturing cost. Based on the manufacturing method, we develop thermoelectric modules.

　We develop thermoelectric power generation systems using existing thermoelectric modules and developed modules. We consider optimization of thermoelectric power generation system by improving efficiency of heat reception from heat medium of medium-temperature waste heat (from 300 to 600 ^oC) and low-temperature waste heat (from 100 to 200 ^oC) , minimizing heat loss.