Physically\nCross-Linked Silk Fibroin-Based Tough Hydrogel\nElectrolyte with Exceptional Water Retention and Freezing Tolerance

Abstract

Flexible\nionic conductive hydrogel is attracting significant interest\nas it could be one of the crucial components for multifunctional ionotronic\ndevices. However, their features of inevitably drying out without\npackage and freezing at subzero temperatures may greatly limit the\napplications of conventional hydrogels in specific situations. Here,\nwe present an ionic conductive hydrogel with water retention and freezing\ntolerance that consists of silk fibroin, ionic liquid, water, and\ninorganic salt. It is discovered that the ionic liquid serves multiple\npurposes to prevent water evaporation, decrease the freezing point,\nprovide the essential conductivity of the hydrogel, etc. As a binary\nmixed solvent, the ionic liquid/water mixture enhances both water\nretention and freezing tolerance of the hydrogel electrolyte. Based\non the silk fibroin (SF)/1-ethyl-3-methylimidazolium acetate (EMImAc)/H₂O/KCl hydrogel electrolyte, the flexible fiberlike supercapacitor\ncould still function well at a temperature as low as −50 °C\nand after being stored in the open air for a long time. It is anticipated\nthat this hydrogel will prove useful in developing new applications\noperating under harsh environments.