Intrinsically Freezing-Tolerant, Conductive, and Adhesive Proton Donor-Acceptor Hydrogel for Multifunctional Applications

Hydrogels have unique liquid-like conductivity and solid-like mechanical properties and are promising materials for a wide range of applications, including tactile sensors and electrolytes for the energy storage device. However, combining suitable mechanical and functional properties in a single hydrogel system remains a central challenge from an application point of view. Besides, freezing of water at subzero temperature severely limits the functional potential of hydrogels. Herein, we have developed a soft yet tough proton donor-acceptor (PDA) hydrogel, combining intrinsic freezing tolerability, conductivity, and adhesiveness with ultrafast complete self-recovery (within 30 s). This unique combination of properties helps us prepare a highly durable tactile sensor (strain, pressure, and temperature) for human motion monitoring at ambient and subzero temperatures. The hydrogels were also used as a matrix to fabricate intrinsically compressible electrolytes for supercapacitor devices. The PDA-based supercapacitors show superior electrochemical performance at ambient temperature and substantially retain it at zero and subzero temperatures. This work also provides a detailed insight into the molecular interactions present in the system and correlates with the bulk mechanical and functional properties, which could guide the development of hydrogels.