Enhanced Thermoelectrochemical Performance via Propylene Glycol-Induced Temperature-Sensitive Crystallization in Redox Flow Batteries

Efficient and cost-effective technologies are highly desired to convert a tremendous amount of low-grade waste heat to electricity. Although the thermally regenerative electrochemical cycle (TREC) has attracted increasing attention, its unsatisfactory thermal-to-electrical conversion efficiency often limits its practical applications. In this work, a strategy based on temperature-sensitive crystallization is demonstrated in a TREC system to boost its thermoelectric performance by rationally regulating the activities of the redox couple at different temperatures. With a Zn anode and a [Fe(CN)6]4–/3– catholyte modified with propylene glycol, the TREC flow cell presents a high temperature coefficient of −2.0 mV K–1 and achieves an apparent thermoelectric efficiency of 6.72% relative to the Carnot efficiency in the temperature range of 25–50 °C. This strategy of using a common industrial solvent to induce a reversible phase transition can inspire research into high-efficiency and cost-effective TREC devices for practical low-grade heat harnessing.