Solvation entropy engineering of thermogalvanic electrolytes for efficient electrochemical refrigeration

Abstract

Emerging thermogalvanic systems can not only convert heat into electricity but also enable electrochemical refrigeration. However, their fundamental electrolytes meet challenges toward high cooling performance due to the absence of rational design principles. Developing thermogalvanic electrolytes with high-temperature coefficients and low heat capacity is the key to efficient electrochemical refrigeration. Here, we report an iron-based electrolyte design strategy by synergistic binary solvent and anion engineering, which rearranges the solvation shell of Fe^2+/3+ ions to achieve a high-temperature coefficient of 3.73 mV K⁻¹ with decreased heat capacity. The comprehensive analyses reveal that the weak Fe^2+/3+-ClO₄⁻ interactions, accompanied by selective association between Fe²⁺ and nitrile solvents, fully enlarge the entropy change available for electrochemical refrigeration. As a result, the optimized electrolyte could potentially reach ∼70% improvement of cooling power, and a direct cooling of electrolyte ∼1.42 K was demonstrated with only 0.11 W cm⁻² input, showing promise for practical electrochemical refrigeration.