Highly Stable Quasi-Solid Thermocells for Continuous Power Generation Across a Broad Humidity Range

Ionic hydrogel-based quasi-solid (IH-QS) thermocells are promising for low-grade heat harvesting, but suffer from humidity-induced instability (i.e., severe dehydration at low humidity and excessive swelling at high humidity), degrading their mechanical and thermoelectric performances. Herein, we develop humidity-stable IH-QS thermocells via the incorporation of amphiphilic networks and hygroscopic electrolytes. This design ensures operational stability across a wide relative humidity (RH) by synergistically combining hydrophilic ─SO₃ ^- groups and hygroscopic electrolytes for high water retention at low humidity and hydrophobic phenyl moieties that form physical crosslinks to suppress swelling at high humidity. Furthermore, the ─SO₃ ^- and phenyl moieties of amphiphilic networks enhance the entropy difference of the [Fe(CN)₆ ^4-/Fe(CN)₆ ^3-] redox couple via electrostatic and ion-π interactions, boosting thermopower. The resulting IH-QS thermocell achieves high thermopower and normalized power density across 30%-99% RH (e.g., 2.17 mV K^-1 and 0.19 mW m^-2 K^-2 at 30% RH; 1.63 mV K^-1 and 0.55 mW m^-2 K^-2 at 99% RH), overcoming a critical barrier to their practical deployment.