Rapid Gelation of Antihydrolyzing Imine Hydrogels with a Stable Cross-Linked Structure for Flexible Sensors and In Situ Assembled Flexible Supercapacitors

Hydrogels based on Schiff base chemistry are widely used for in situ applications due to their rapid gelation property. However, the inherent hydrolytic instability and dynamic nature of imine bonds limit their use in scenarios requiring long-term structural stability and stress relaxation resistance, especially in non-neutral pH environments. Herein, we report an imine hydrogel with a stable cross-linked network that exhibits enhanced resistance to hydrolysis. The hydrogel forms rapidly (<3 min) through condensation between aldehyde groups from glutaraldehyde (GA) and primary amines (-NH₂) generated by the deprotonation of -NH₃⁺ groups on poly(allylamine hydrochloride) (PAH). Multipoint cross-linking between PAH and GA not only facilitates the rapid gelation process at low pH value but also imparts a robust and resilient network, enabling exceptional hydrolytic stability even under strongly acidic conditions. Based on these properties, the hydrogel can be employed as a stable acidic polyelectrolyte in the domains of signal sensing and energy storage. With moderate incorporation of LiBF₄, the hydrogel can be used to fabricate antifreezing sensors for real-time monitoring of laryngeal activity or finger movements. Furthermore, the rapid gelation kinetics facilitate in situ assembly of flexible supercapacitors within 15 min, which maintain practical and stable energy storage properties after 1 h of gelation. The resulting supercapacitors demonstrate high specific capacitance (124.1 F g^-1), an energy density (<i>E</i>) of 17.1 Wh kg^-1, and stable interfacial contact during deformation, with ideal cycling stability of over 5000 charge-discharge cycles without packaging. This work provides a strategy for rapid preparation of stable hydrated imine polymers, particularly suitable for field-based in situ fabrication of polyelectrolytes for electronic and energy storage devices.