Potassium AMTEC Cell Performance

AMTEC systems have historically been operated with sodium as the working fluid, in large part because fabrication of beta”-alumina solid electrolyte (BASE) membranes has been substantially easier with sodium than with potassium or other alkali metals¹. It has been anticipated that because potassium has a substantially higher vapor pressure for a given temperature, and because the best K-BASE conductivity falls only marginally below that for Na-BASE, potassium AMTEC cells could produce higher power at a given temperature or comparable power at a lower temperature than similar sodium cells. Operation at lower temperatures can reduce materials lifetime or compatibility problems, and for severely heat input constrained systems it could enhance efficiency by reducing parasitic thermal conduction losses. Recently K-BASE tubes have become available as a commercial product² and conventional experiments to evaluate the performance of complete KAMTEC cells have become much more feasible. Previous experiments on K-BASE have focused primarily on measurements in non-power producing cell environments. One AMTEC cell experiment was carried out at low temperature.³ We report here initial experiments on the power output performance of KBASE with a conventional TiN cathode in a standardized single-pass AMTEC test cell. The performance data are compared to tests of Na-BASE cells under similar conditions and with similar electrodes. Peak power for a 6 cm² TiN electrode on a K-BASE cell was substantially higher than has been observed for the best, comparable Na-BASE cells. The power improvement corresponded to that for a temperature increase of ~ 60 K for the Na- BASE cell.