Stretchable and Freeze‐Tolerant Organohydrogel Thermocells with Enhanced Thermoelectric Performance Continually Working at Subzero Temperatures

Abstract Aqueous thermocells that are eco‐friendly and capable of converting low‐grade heat into electricity continuously are promising candidates to power flexible and wearable devices in various application scenarios. However, challenges remain in their limited working temperatures, mechanical fragility, and poor thermoelectric performance, mainly due to the reduced entropy of both polymer chains and thermogalvanic ions at low temperatures. In this work, the challenges are addressed by introducing a synergistic chaotropic effect to destruct strong hydrogen bonds, increase polymers’ entropic elasticity, and enlarge the entropy difference of thermogalvanic ions. An organohydrogel thermocell is designed with a chaotropic comonomer and a chaotropic cosolvent. The maximum normalized power density of the thermocell achieves 0.1 mW m −2 K −2 , which is in the same order of magnitude as the highest record in current quasi‐solid thermocells. Even at −30 °C, the thermocell maintains the elongation at a break of more than 100% and a relatively high power density of 0.012 mW m −2 K −2 . Furthermore, the thermocell shows the potential to light up a light‐emitting diode and stably works when compressed, bent, and stretched in a wide temperature range. This work provides insights on developing reliable power sources to drive flexible electronics continually in extremely cold environments.