Thermopower regulation of thermocells via electrolyte engineering: progress and prospects

Abstract

Thermocells (TECs) represent a promising technology for sustainable low-grade waste heat (<100 °C) harvesting, offering distinct advantages such as scalability, structural versatility, and high thermopower. However, their practical applications are still hindered by low energy conversion efficiency and stability issues. In recent studies, electrolyte engineering has been highlighted as a critical strategy to enhance their thermopower by regulating the solvation structure and redox ion concentration gradient, thereby improving conversion efficiency. This review comprehensively summarizes progress in optimizing electrolytes for TECs, focusing on tailored strategies for four representative redox couples, namely, Fe(CN)₆^4−/3−, Fe^2+/3+, I⁻/I₃⁻, and Cu/Cu²⁺. Key approaches, including modulating solvation structures via additives or co-solvents to amplify solvation entropy, and leveraging thermosensitive crystallization or phase separation to establish a redox ion concentration gradient, are thoroughly discussed. These discussions cover both liquid- and gel-type TECs, emphasizing performance enhancements in thermoelectrochemical Seebeck coefficients and normalized power densities, as well as advancements in device integration and applications. In the last section, challenges in efficiency, mass transfer, and long-term stability are critically proposed, highlighting potential directions for the future development of high-performance TECs.