Super strong gelatin/cellulose nanofiber hybrid hydrogels without covalent cross-linking for strain sensor and supercapacitor

Natural polymer hydrogels are considered to be excellent candidates for eco-friendly flexible devices. However, the defects of low strength and poor toughness result in their being easily damaged. Here, strong gelatin-based hydrogels enhanced by hydrophobic aggregation were prepared using salting-out treatment. Moreover, the cellulose nanofiber (CNF) with large aspect ratio further improved the mechanical strength relying on the intertwining effect. The optimized strong hybrid gelatin/CNF hydrogel achieved 0.73 MPa of breaking strength and 250% of elongation at break, 405 and 8.3 times that of the original hydrogel, respectively. Notably, the gelatin/CNF hydrogel exhibited satisfactory conductivity and excellent linear sensing behavior, allowing it to monitor human motions accurately. Besides, this robust gelatin-based hydrogel could be used as supercapacitor electrolyte and showed desirable rate capability and good cycling stability. This work implies a bright future for the application of gelatin-based hydrogel in the field of environmentally friendly energy storage devices and sensors.