Highly stretchable ionic hydrogels with enhanced thermoelectric performance and flame retardancy for intelligent fire protection†

Fire disasters pose a significant threat to life and property worldwide, underscoring the urgent necessity for advanced fire prevention technologies. In the field of intelligent fire protection materials, thermoelectric fire-resistant materials have garnered considerable attention due to their high sensitivity and the distinct advantage of not requiring an external power supply. This feature endows them with high responsiveness and energy efficiency in detecting and responding to fire incidents, thereby enhancing overall safety measures. In this study, we develop a series of highly stretchable ionic hydrogels with exceptional thermoelectric properties and flame retardancy for intelligent fire protection applications. Through a simple one-pot photopolymerization process, polyacrylic acid (PAA) and polyethylene glycol (PEO) were combined with sodium dihydrogen phosphate (SDP) to form a robust hydrogen-bonded ionic hydrogel network. The resulting PAA-PEO-SDP ionic hydrogels demonstrated an impressive elongation at break up to 4270% and a very high ionic Seebeck coefficient of 24.7 mV K⁻¹. The incorporation of the phosphorus salt enhanced flame retardancy to reach the UL-94 V-0 rating and significantly increased the oxygen index of encapsulated wood from 27% to 54%. Moreover, as a fire-warning device, it could rapidly generate an output voltage of ca. 50 mV within 1.5 s upon exposure to fire, showcasing potential for autonomous fire prevention systems. This work highlights the synergistic integration of mechanical flexibility, thermoelectric performance, and fire safety in the development of next-generation intelligent materials for fire protection.