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 a high thermopower of 3.76 mV·K⁻¹ and a 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, and 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.