Water‐Thermal Self‐Cycling Thermoelectric Hydrogel for Continuous Energy Harvesting from Body Heat

Abstract The ability to continuously harvest energy from the human body has immense potential for powering wearable devices and biomedical systems, yet current thermoelectric hydrogels are constrained by rapid dehydration, limiting operational lifespans to less than 120 m and achieving temperature gradients of only ≈5 °C. Here, a self‐cycling thermoelectric hydrogel is presented that addresses these challenges by autonomously regulating water‐thermal cycling. This strategy achieves a maximum temperature gradient of 13 °C—more than 2.6 times the state‐of‐the‐art—and maintains stable thermoelectric output for over 1500 min, the longest lifespan reported for such materials. Additionally, the hydrogel fully recovers hydration within 5 h, enabling robust reusability. Mechanistic studies reveal that optimized ionic interactions enhance thermal diffusion and elevate the Seebeck coefficient to 4.1 mV K −1 . This study introduces a scalable design for wearable thermoelectric materials, paving the way for advancements in health monitoring, environmental sensing, and wearable electronics.