Advanced designs on thermally regenerative electrochemical cycle for low-grade heat harvesting

Abstract

With the increasingly severe energy crisis and the growing demand of carbon neutralization, clean energy has become an imperative global priority. Among the clean energy, heat source is ubiquitous, and various technologies have been developed to harvest the waste heat. By utilizing the thermogalvanic effect of electrode materials, thermally regenerative electrochemical cycle (TREC) could effectively convert the low-grade periodic temperature difference into electricity. In this thesis, I propose advanced designs on TREC to overcome the obstacles limiting the application of TREC. To address the challenge of harvesting ultralow-grade heat, thermally responsive ionic liquid is introduced to the TREC system. By involving both electrode and electrolyte in temperature change processes, the energy conversion efficiency is significantly increased, particularly when the temperature difference is minimal. Besides, I explore the thermogalvanic effect of the overlooked pseudocapacitor electrode material. Ti3C2 and Ag/AgCl are proved to be ideal electrodes for operating charge-free TREC owing to their approaching open circuit voltages and moderate equilibrium temperature, suggesting new candidates of pseudocapacitive materials being utilized as the electrode of TREC system. Furthermore, the operating conditions of the charge-free TREC system are systematically studied to obtain the optimal energy harvesting performance. With the optimized electrolyte system, a practical application of powering a calculator has been successfully demonstrated for the first time, verifying the feasibility of the system. The thesis provides new prospectives for optimizing the energy conversion efficiency, effectively harnessing ultralow-grade thermal energy, extending the range of electrode choices, and expanding the potential applications of TREC technology.