Johnson Thermo-Electrochemical System for Ultra-High Efficiency Heat to Electrical Energy Conversion

Abstract:

The energy needs of NASA space missions are broad and require a scalable device capable of generating large and small amounts of power for applications as large as aircraft propulsion or as small as a smallsat/cubesat. NASA has a long history of using solid state thermoelectric couples in Radioisotope Thermoelectric Generators (RTGs) to convert heat into electricity. Unfortunately, over the past five decades, existing thermoelectric converters have only achieved a net efficiency of less than 6%.

The Johnson Thermo-Electrochemical Converter (JTEC) is a high efficiency, solid state, direct heat to electric converter that is projected to achieve over 40% conversion efficiency operating at equivalent heat source temperatures. JTEC has no moving mechanical parts. The technology can provide NASA an attractive replacement for its existing low efficiency thermoelectric converters. In addition, the JTEC offers the versatility of operating on a wide range of heat sources, from low grade waste heat sources to high temperature primary heat sources including solar, thermal and nuclear applications.

A proof-of-concept JTEC with polybenzimidazole (PBI) as the proton exchange membrane (PEM) comprising of a 200 °C heat source and 25°C heat sink recently reached 17% efficiency. Much higher conversion efficiency and much higher generated power densities are theoretically feasible in the JTEC by replacing the polymer PEM with a ceramic PEM. We are on track to design a perovskite-based complex oxide JTEC, more than doubling the original conversion efficiency.