Unraveling Reaction Kinetics and Thermodynamics in Thermogalvanic Hydrogels: A Pathway to Efficient Thermal Energy Harvesting

Abstract

Thermogalvanic (TG) systems generate electricity by exploiting the temperature-dependent electrochemical potential established across a temperature gradient. While previous studies have attributed performance enhancements to increased reaction entropy driven by changes in solvation structure, the interplay between entropy variations and reaction kinetics has not been systematically explored through electrochemical analysis. This study presents a comprehensive investigation of formamide (FA)/water-based TG hydrogels. Electrochemical analyses reveal that FA/water systems exhibit significantly higher reaction entropy compared to pure water systems, thus leading to enhanced thermopower. More importantly, the reaction kinetics of the TG hydrogels are examined using a stationary electrode for the first time. The results indicate that low FA concentrations promote the desolvation of redox ions, thereby accelerating the reaction kinetics and increasing the short-circuit current density. In addition, FA acts as a stabilizer for water, thereby lowering the activation energy of the redox reaction and resulting in a remarkable 60% improvement in overall thermoelectric power. This work provides insights into the fundamental mechanisms governing FA/water TG hydrogels and emphasizes the critical role of reaction kinetics in optimizing the thermoelectric performance for thermal energy harvesting applications.