text: Single-cell AMTECs with open voltages as high as 1.55 V and maximum power density as high as 0.50 W/cm of solid electrolyte area at a temperature of 1173 K (900 °C) have been obtained with long-term stable refractory metal electrodes.
  Efficiency of AMTEC cells has reached 16% in the laboratory. High-voltage multi-tube modules are predicted to have 20–25% efficiency, and power densities up to 0.2 kW/L appear to be achievable in the near future. Calculations show that replacing sodium with a potassium working fluid increases the peak efficiency from 28% to 31% at 1100 K with a 1 mm thick BASE tube.
  Most work on AMTECs has concerned sodium working fluid devices. Potassium AMTECs have been run with potassium beta″-alumina solid electrolyte ceramics and show improved power at lower operating temperatures compared to sodium AMTECs.
  A detailed quantitative model of the mass transport and interfacial kinetics behavior of AMTEC electrodes has been developed and used to fit and analyze the performance of a wide variety of electrodes, and to make predictions of the performance of optimized electrodes.  The interfacial electrochemical kinetics can be further described quantitatively with a tunneling, diffusion, and desorption model. A reversible thermodynamic cycle for AMTEC shows that it is, at best, slightly less efficient than a Carnot cycle.
  A related technology, the Johnson thermoelectric energy converter, uses a similar concept of pumping positive ions through an ion-selective membrane, using hydrogen rather than an alkali metal as the working fluid.