Self-Healable, High-Strength Hydrogel Electrode for Flexible Sensors and Supercapacitors

Flexible energy storage materials and sensors have become the key equipment of human-machine interface technology. For the preparation of these devices, hydrogel electrodes are relevant because of their unique porous structure, high capacitance, flexibility, small size, and lightweight. In this paper, regular polypyrrole (PPy) is synthesized on a heat-induced phase-separated gel (H-Gel/AS) by the template degradation method, and a gelatin-based PPy hydrogel with high strength, high strain rate, and high conductivity is prepared. Moreover, by adding multiwalled carbon nanotubes (MWCNTs) into a gelatin solution according to the H-Gel/AS method, the electrochemical performance of the resulting H-Gel/AS-MWCNTs-PPy electrode is greatly improved. When the H-Gel/AS-MWCNTs-PPy gel is immersed in an ammonium sulfate solution, wrinkles appear on the surface, resulting in further enhancement of the capacitance. On this basis, a flexible sensor and a solid-state supercapacitor are assembled, and their performance is tested. The sensor can detect tensile, bending, and twisting strains with high sensitivity. Meanwhile, as a flexible solid-state supercapacitor, the specific capacitance is 75 F g^-1, and the capacitance retention rate after 5000 cycles is 98.1% under bending conditions. More importantly, the gelatin-based hydrogel shows great potential for application in wearable devices.