Thermosensitive crystallization-boosted thermoelectric hydrogels for self-powered sensing and intelligent perception applications

Wearable sensing technology has seen widespread use in health monitoring, environmental perception and human-machine interaction. Among them, sensors that can actively harvest energy from their application scenarios to achieve self‑powering are especially favored. In this study, we developed a polyacrylic acid (PAA)-based ionic thermoelectric hydrogel of PAA-K₃Fe(CN)₆/K₄Fe(CN)₆-guanidinium chloride (GdmCl) hydrogel (PFGH). Under temperature difference driving, redox reactions within the hydrogel directly convert thermal energy into electrical signals. The introduction of GdmCl induces K₄Fe(CN)₆ to form thermosensitive crystals, significantly enhancing entropy differences between redox couples. This design enables PFGH to achieve high thermopower of 3.76 mV/K and normalized power output density of 37.77 mW·m^-2·K^-2. Additionally, hydrogen bonding between PAA and [Fe(CN)₆]^3-/4- ions enable PFGH with excellent mechanical properties (tensile strength of 90 kPa, elongation at break of 920%). With excellent thermoelectric and mechanical properties, PFGH demonstrates outstanding application potential in wearable sensing fields, achieving diversified functions including self-powered motion monitoring, real-time respiratory status perception, intelligent fire warning, and machine learning-assisted material identification. This study paves the way for next-generation self-powered wearable devices and unlock new possibilities for body heat utilization in smart sensing applications.