Electrochemical Peltier Cooling: Device Design, Measurement Techniques, and Molecular Optimization.

The electrochemical Peltier (ECP) effect utilizes the entropy change of a redox reaction to cool the electrolyte. This perspective aims to provide an overview of the ECP effect, from its fundamental principles and historical studies to recent developments in ECP-based refrigeration, emphasizing strategies to enhance performance through both device engineering and molecular design. A standard measurement protocol is proposed for the quantitative analysis of the intrinsic ECP effect that is separated from the temperature fluctuation of the experimental environment and irreversible thermal processes such as Joule heating. Recent device engineering, including the circulation of the liquid electrolyte and the combination of two different redox pairs to form the p-n junction, shows a drastic improvement in the refrigeration. Moreover, recent molecular approaches, including supramolecular host-guest interactions, proton-coupled electron transfer (PCET) reaction, and redox-induced coil-globule transitions, have demonstrated significant enhancement in the redox entropy and cooling performance. These studies reveal that interdisciplinary collaboration among thermal engineering, electrochemistry, and supramolecular chemistry has led the today's successful development of the ECP refrigeration technology.