An electric double-layer capacitor-based heat flow switching device working with a bias voltage was developed as a key technology of thermal management. This device allows us to rapidly control the magnitude of heat flow passing through the device using variations in electronic thermal conductivity of component material induced by the bias voltage. We employed a thin film of Ag₂S_0.8Se_0.2 as the most important component material, because it possesses an exceptionally low lattice thermal conductivity and a semiconducting electronic structure. The thermal conductivity of the fabricated device was measured by means of a periodic heating method under various applied bias voltages. The thermal conductivity of Ag₂S_0.8Se_0.2 was found to increase linearly with increasing bias voltage V_B up to a factor of 1.9 at V_B = 2.4 V. The transient current response during the charging and discharging processes revealed that the response time for switching was fast enough to be less than 0.2 sec. By measuring the stored charge and comparing it with the electronic thermal conductivity, we confirmed that the observed variation in thermal conductivity of the component material is attributed to the accumulated charge in the material.

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A thermoelectric power generation unit that efficiently utilizes exhaust steam has been developed. A prototype 1 kW-class power generation system was evaluated at a hot spring resort using self-heated steam. The final power output was 373 W, limited by insufficient cooling water. For practical application of thermoelectric power generation, it is essential to reduce system costs, select an appropriate waste heat source and installation site, and optimize the entire system, including power conversion and utilization．

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Thermal management technologies have attracted considerable interest from demands on energy saving, carbon neutral, the temperature control of nano-scale devices, etc. In this study, we developed a thin-film heat-flow switching-device working with small variation of device temperature by making full use of the unique temperature dependence of the thermal conductivity of Ag₂+_αS_xSe_1－x. Their thermal conductivity was carefully investigated using the time-domain thermoreflectance (TDTR) method, and a large variation of thermal conductivity exceeding κ_{_large} /κ_{_small} = 2.5 was observed. We found that this large variation in hear flux was caused by a thermal pumping phenomenon attributed to the latent heat at the phase transition of Ag₂+_αS_xSe_1－x. To gain a deeper insight into the thermal pumping phenomenon, we investigated the composition and thickness dependence of heat flux change for the devices consisting mainly of Ag₂+_αS_x Se_1－x. Larger changes both in entropy and phase transition volumes resulted in a significant increase in heat absorption. An improved devices was developed with the optimized composition and the optimized film thickness, and the heat flux of the optimized device showed an extraordinary value of J_{Q_large} / J_{Q _small} approximately equal to 30 - 40 induced by 5 K change in device temperature.

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