Simultaneously Modulating Solvation and Water Structurefor High-Performance Antifreezing <i>n</i>‑Type LiquidThermocells

Emerging ionic thermoelectric (i-TE) modules consisting of <i>p</i>–<i>n</i> liquid thermocell arrays provide compact and cost-effective ways to achieve low-grade heat harvesting. Despite exciting progress in <i>p</i>-type thermocells, high-performance <i>n</i>-type thermocells remain underdeveloped. Here we present an <i>n</i>-type liquid thermocell with a cosolvent antifreezing electrolyte showing enhanced thermopower, record-high efficiency and power density, and the capability to harness both low-grade heat and subfreezing coldness. Acetonitrile is used as the cosolvent molecule with water that can selectively pair with the reduced metal ion only and simultaneously disrupts the water structure. By tailoring these molecular interactions, we achieved a record-high Carnot-relative efficiency of 1.9% among reported <i>n</i>-type thermocells, and a power density of 5.5 W/m² at the hot/cold temperatures of 69.8 °C and −19.5 °C, respectively. Our work marks an important advancement in i-TE technology in terms of both molecular insights and the preparation of high-performance <i>n</i>-type liquid thermocells for low-grade heat harvesting.