Efficient Low‐Grade Heat Harvesting Enabled by Tuning the Hydration Entropy in an Electrochemical System
Caitian Gao, Yezhou Liu, Bingbing Chen, Jeonghun Yun, Erxi Feng, Yeongae Kim, Moobum Kim, Ahreum Choi, Hyun‐Wook Lee, Seok Woo Lee
Abstract
Abstract Harvesting of low‐grade heat (<100 °C) is promising, but its application is hampered by a lack of efficient and low‐cost systems. The thermally regenerative electrochemical cycle (TREC) is a potential alternative system with high energy‐conversion efficiency. Here, the temperature coefficient (α), which is a key factor in a TREC, is studied by tuning the hydration entropy of the electrochemical reaction. The change of α in copper hexacyanoferrate (CuHCFe) with intercalation of different monovalent cations (Na + , K + , Rb + , and Cs + ) and a larger α value of −1.004 mV K −1 being found in the Rb + system are observed. With a view to practical application, a full cell is constructed for low‐grade heat harvesting. The resultant η e is 4.34% when TREC operates between 10 and 50 °C, which further reaches 6.21% when 50% heat recuperation is considered. This efficiency equals to 50% of the Carnot efficiency, which is thought to be the highest η e reported for low‐grade heat harvesting systems. This study provides a fundamental understanding of the mechanisms governing the TREC, and the demonstrated efficient system paves the way for low‐grade heat harvesting.