Mechanically Robust Thermoelectric Hydrogel with Superior Thermoelectricity for Low-Grade Thermal Energy Harvesting and Overheating Warning

Ionic thermoelectric (i-TE) hydrogel, combined with intrinsic softness, conductivity, and thermoelectricity, is a highly promising candidate for flexible thermoelectric materials to directly harvest low-grade thermal energy from the environment and the human body. However, efficiently converting heat into electricity without compromising structural robustness under extreme mechanical conditions is of great significance but still challenging. Herein, we prepared a poly(vinyl alcohol) (PVA)/sodium alginate (SA)/NaCl/Fe(CN)63-/4- (PSNF) hydrogel with superior mechanical robustness and thermoelectricity, utilizing the combination of a dual thermoelectric effect by the freeze/thaw method and the Hofmeister effect. Leveraging the advantages of abundant ion transport channels for ion transport at two poles and the efficient energy dissipation of a toughening structure, the PSNF hydrogel delivers a collection of merits, including superior mechanical integrity (toughness up to 1750 kJ·m-3) and exceptional conductivity (12.11 mS·cm-1), an impressive high Seebeck coefficient (Se) (1.71 mV·K-1) and a power factor (PF) (3.54 μW·K-2·m-1). As a proof of concept, the assembled thermoelectric integrated device achieves the conversion of heat into electrical energy to drive a bulb array, which can harness stable thermosensation for overheating warnings even under continuous cyclic temperature changes. It is believed that this work may provide insights into the development of robust thermoelectric hydrogels for thermal energy harvesting and overheating warning devices.