Thermodynamic engines have inherent difficulties in achieving high compression ratios and in achieving the near constant temperature compression and expansion processes needed to approximate Carnot equivalent cycles. Solid-state thermoelectric converters that utilize semiconductor materials have only been able to achieve single digit conversion efficiency. Alkali Metal Thermoelectric Converters (AMTEC), which operate on a modified Rankine cycle and the Stirling engine, have inherent limitations and these systems have not achieved performance levels as envisioned.
The Johnson Thermo-Electrochemical Convertor (JTEC) is an all solid-state device that operates on the Ericsson cycle. Equivalent to Carnot, the Ericsson Cycle offers the maximum theoretical efficiency available from a converter operating between two temperatures. The JTEC system utilizes the electro-chemical potential of fluid pressure applied across a proton conductive membrane (PCM). The membrane and a pair of electrodes form a Membrane Electrode Assembly (MEA) similar to those used in fuel cells. However, in the JTEC the hydrogen circulates continually inside the device, which is different from a fuel cell in which hydrogen is consumed and must be continually replenished.