Efficient low-grade heat conversion and storage with an activity-regulated redox flow cell via thermally regenerative electrochemical cycle.

Abstract

Efficient and cost-effective technologies are highly desired to convert the tremendous amount of low-grade waste heat to electricity. Although thermally regenerative electrochemical cycle (TREC) has attracted increasing attention recently, the unsatisfactory thermal-to-electrical conversion efficiency and low power density limit its practical applications. In this work, we demonstrate a thermosensitive Nernstian-potential-driven strategy in TREC system to boost its temperature coefficient, power density and thermoelectric conversion efficiency by rationally regulating the activities of redox couples at different temperatures. With Zn anode and [Fe(CN)6 ]4-/3- -guanidinium as catholyte, the TREC flow cell presents an unprecedented average temperature coefficient of -3.28 mV/K, and has achieved an absolute thermoelectric efficiency of 25.1% and apparent thermoelectric efficiency of 14.9% relative to Carnot efficiency at the temperature range of 25-50 °C at 1 mA/cm2 . In addition, a thermoelectric power density of 1.98 mW/(m2 K2 ) has been demonstrated, which is more than 7 times the highest power density of reported TREC systems. This activity regulation strategy could inspire research into high-efficiency and high-power TREC devices for practical low-grade heat harnessing. This article is protected by copyright. All rights reserved.