Physically Crosslinked Silk Fibroin Based Tough Hydrogel Electrolyte with Exceptional Water-Retention and Freezing-Tolerance.

Flexible ionic conductive hydrogel is attracting massive interests as it could be one of the crucial components for multifunctional ionotronic devices. However, their features of inevitably drying out without package and freezing at subzero temperature may greatly limit the applications of conventional hydrogels in specific situations. Here, we present an ionic conductive hydrogel with water-retention and freezing-tolerance which consists of silk fibroin, ionic liquid, water and inorganic salt. It is discovered that the ionic liquid serves multiple roles to prevent water evaporation, decrease the freezing point and provide the essential conductivity of the hydrogel, etc. As a binary mixed solvent, the ionic liquid/water mixture enhances both water-retention and freezing-tolerance of the hydrogel electrolyte. Based on SF/EMImAc/H2O/KCl hydrogel electrolyte, the flexible fiber-like supercapacitor could still function well at a temperature as low as -50 masculineC and after being stored in the open air for a long time. It is anticipated that this hydrogel will prove useful in developing new applications operating under harsh environments.