Study on the electrode characteristics of alkali metal thermoelectric converter

The alkali metal thermoelectric converter utilizing the sodium ion conducting β''-alumina is a device to convert directly heat energy to electric energy. It is characterized by high conversion efficiencies, high power densities, no moving parts and low maintenance requirements. Because of these merits, AMTEC is one of the most promising candidate for aerospace power systems, remote power station and dispersed small scale power station. In this paper, the experimental results of the disk type cell and the theoretical considerations about internal resistances have been reported. The film electrode was made with a magnetron sputtering system. The open voltage of 0.98 V and the maximum power density of 0.38 W/cm2 at the sodium temperature of 1,073 K have been obtained. It became clear after the theoretical investigation on the internal resistance that the most largest internal resistance was the resistance of β''-alumina. And so, it is necessary to reduce the thickness of β''-alumina to improve the generating power densities. It was also clarified that the sodium gas flow in the small holes of molybdenum thin film electrode was a free molecular flow and the experimental results became agree well with the theoretical results considering the pressure rise due to this sodium free molecular flow. It was also necessary to develop the more porous and lower resistivity thin film electrodes because this pressure rise were fairly large. (author)