A figure of merit for AMTEC electrodes

As a method to compare the results of alkali metal thermoelectric converter (AMTEC) electrode performance measured under different conditions, an AMTEC figure of merit called ZA is proposed. This figure of merit is the ratio of the experimental maximum power for an electrode to a calculated maximum power density as determined from a recently published electrode performance model. The calculation of a maximum power density assumes that certain loss terms in the electrode can be reduced to essentially zero by improved cell design and construction, and that the electrochemical exchange current is determined from a standard value. Other losses in the electrode are considered inherent to the electrode performance. Thus, these terms remain in the determination of the calculated maximum power. A value of ZA near one, then, indicates an electrode performance near the maximum possible performance. The primary limitation of this calculation is that the small electrode effect cannot be included. This effect leads to anomalously high values of ZA. Thus, the electrode area should be reported along with the figure of merit.