This paper describes the design of high-efficiency reversible thermoelectric conversion devices for thermoelectric power generation through liquid potassium-ammonia (K-NH 3 ) solutions. The validity and effectiveness of the proposed design is verified by thermoelectric experiments using two kinds of "U"-shaped vacuum cells with a NH 3 -gas passageway connecting both legs of "U", one of which has a waist in the middle of a liquid flow passage. The experimental results show that the gas passageway provides a stable and reliable reaction by preventing an internal pressure imbalance due to NH 3 gasification during solution decomposition; hence, long-term, reversible thermoelectric power can be effectively derived by stably inducing two separate phase transitions in the cell. In addition, the effect of the narrow waist in the cell's middle is verified to cause an increase in thermoelectric conversion efficiency due to improved electric conductivity of liquid in the vacuum cell. Consequently, using these technologies in thermoelectric cell potentially leads to long-time, high-efficiency thermoelectric power generation through liquid K-NH 3 solutions.

− Lithium-ammonia (Li-NH 3 ) solutions are possible to be successfully made under the vacuum condition but there still remains a problem of undergoing stable and reliable decomposition in vacuum for high-efficiency thermoelectric power generation. This paper describes a new method for improving the thermoelectric conversion efficiency of Li-NH 3 solutions in vacuum. The proposed method uses a 'U'-shaped Pyrex vacuum tube for the preparation and decomposition of pure fluid Li-NH 3 solutions. The tube is shaped so that a gas passageway ('U') connecting both legs of the 'U' helps to balance pressure inside both ends of the tube (due to NH 3 gasification) during decomposition on the hot side. Thermoelectric experimental results show that solution reaction in the 'U'-shaped tube proceeds more stably and efficiently than in the 'U'-shaped tube, and consequently, thermoelectric conversion efficiency is improved. It is also proved that the proposed method can provide a reversible reaction, which can rotate between synthesis and decomposition in the tube, for deriving the long-time, high-efficiency thermoelectric power.