Agarose/polyvinyl alcohol double-network hydrogel with excellent anti-freezing properties for moisture-electric generators and self-powered respiratory monitoring sensors.

Moisture-electric generators (MEGs) can utilize water vapor in the air to provide energy. In recent years, hydrogel-based MEGs have gradually become a research direction of great importance due to the excellent electrical conductivity and mechanical properties of hydrogels. However, most hydrogels have poor anti-freezing properties, which greatly limits the application of MEGs. In this work, PVA/AG/AMPS/PA-LiCl (PAAP-L) hydrogels were successfully synthesized via one-pot and immersion methods using polyvinyl alcohol (PVA), agarose (AG), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), phytic acid (PA), and LiCl. The hydrogel exhibits excellent anti-freezing and moisture-retaining properties, with a freezing point as low as -66.58 °C and a high conductivity of 7.61 S/m, enabling it to serve as a strain sensor for detecting human movement. More importantly, a MEG was successfully developed based on this hydrogel, which quickly generated an open-circuit voltage of up to 622 mV within 6 s of exposure to humid air. In addition, the hydrogel successfully addressed the limitation of its inability to function as a self-powered respiratory monitor under low-temperature conditions, enabling it to sensitively monitor human respiratory patterns. The PAAP-L hydrogel in this study broadens the application scope in the fields of green energy and self-powered respiratory monitor sensors.