Gelatin-Based Freeze-Resistant Hydrogel Supercapacitors with Oriented Porous Structure

Capacity, mechanical flexibility, and anti-freezing properties are crucial for all-in-one hydrogel-based supercapacitors. Herein, a mechanically flexible, freeze-resistant, all-in-one gelatin-based supercapacitor is presented with significantly improved areal capacity, achieved through an oriented porous structure in the hydrogel electrolyte. The gelatin-based hydrogel electrolyte is prepared via a facile gelation-directional-freezing process, generating an oriented porous structure that is well preserved in the α-methyl group-stabilized, hydrogen-bond-reinforced gelatin/poly(methyl acrylic acid) network. The all-in-one supercapacitor is fabricated through in situ polymerization of polypyrrole (PPy) on the hydrogel electrolyte. The highly oriented porous structure not only enhances ionic conductivity but also promotes PPy growth into its framework, thereby improving electrode-electrolyte interaction and charge transfer efficiency for superior areal capacitance. The capacity of the supercapacitor with an oriented porous structure is 3.5 times higher than that of its non-oriented counterpart. The anti-freezing hydrogel supercapacitor is fabricated by incorporating a glycerol/water binary solvent. Due to excellent ion-transport properties and PPy growth into the hydrogel, the device achieved a high capacitance retention of 77.2% at -23 °C. It also endured 100 cycles of stretching, compression, and bending without significant performance degradation, demonstrating excellent anti-freezing properties, flexibility, and structural stability.