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Thermally regenerative electrochemical cycle for low-grade heat harnessing

Low-grade heat (<100 °C) from natural sources, electronics, and industrial plants is abundant and ubiquitous and has great potential to be converted to electricity. Thermally regenerative electrochemical cycle is a promising method for effectively converting low-grade heat into electricity. In this review, the operating mechanism of thermally regenerative electrochemical cycle systems and the ways of evaluating their thermoelectric performance, based on apparent and absolute thermoelectric efficiency, are first introduced. The recent progress of electrically assisted thermally regenerative electrochemical cycle systems including the static, flow, redox targeting-based flow, and charging-free thermally regenerative electrochemical cycle systems is then critically reviewed. Although substantial progress has been made, challenges such as unsatisfactory thermoelectric efficiency, low power density, poor stability at high temperatures, and high cost remain, which hinders the practical use of thermally regenerative electrochemical cycle for low-grade heat harnessing. A perspective is thus provided with suggestions from the material aspects to system optimizations, which could potentially lead to a boost of the thermoelectric performance of thermally regenerative electrochemical cycle systems for practical applications.