Redox Targeting-Based Thermally Regenerative Electrochemical Cycle Flow Cell for Enhanced Low-Grade Heat Harnessing

Abstract

A large amount of low-grade heat (<100 °C) is produced in electrical devices and mostly wasted. This type of heat without effective dissipation also causes compromised device performance, reliability, and lifespan. To tackle these issues, a redox targeting (RT)-based flow cell with judiciously designed thermoelectrically active redox materials is demonstrated for the first time for efficient heat-to-electricity conversion through a thermally regenerative electrochemical cycle (TREC). Compared with the conventional TREC systems, the RT-based flow cell not only reveals considerably enhanced thermoelectric efficiency, but the flow of redox fluids also provides a cooling function to the system. In this work, solid material Ni_0.2 Co_0.8 (OH)₂ and redox mediator [Fe(CN)₆ ]^4-/3- , both of which have negative temperature coefficient and share identical redox potential, are paired via RT-reactions to boost the capacity and meanwhile thermoelectric efficiency of a [Fe(CN)₆ ]^4-/3- /Zn^0/2+ -based flow cell. Upon operating over the TREC cycle, the RT-based flow cell converts heat to electricity at an unprecedented absolute thermoelectric efficiency of 3.61% in the temperature range of 25-55 °C.

Keywords: low-grade heat harnessing; redox flow batteries; redox targeting; thermally regenerative electrochemical cycles.