Evaluation of thermally regenerative electrochemical cycle for thermal-to-electrical energy conversion

A significant amount of low-grade heat (< 100 ?) can be found in various sources, such as geothermal/solar sources, industrial plants, vehicles, and biological entities, but it is often wasted due to the absence of cost-effective and efficient recovery technologies. Thermally regenerative electrochemical cycle (TREC) represents a promising solution for effectively harnessing low-grade heat. Rapid advancements in TREC chemistry, materials, and design have established the crucial foundations for high-power, efficient, and long-lasting TREC systems. However, evaluating the potential of reported TREC systems of different types is challenging due to the inconsistency in evaluation metrics and methods. In this Perspective, we examine the working principle of various TREC systems, including the electrically powered TREC systems, charging-free TREC systems that solely convert thermal energy to electrical energy, and TREC systems that simultaneously provide high-power energy storage and thermal energy conversion. The critical performance metrics for each of these three types of TREC systems, such as absolute/apparent thermoelectric efficiency, power density, net electricity generation, various forms of energy loss, and thermal energy input, are presented to compare the thermoelectric performance across different types of TREC systems at various scales. In addition, some practical methods for measuring the critical parameters, current challenges, and future directions for practical applications are also highlighted.