Supramolecular Self-Assembled, Conductive, Mechanically Flexible MXene Cross-Linked Polypyrrole Hydrogel for Wearable Energy Storage Applications.

Abstract

Wearable supercapacitors, an emerging integrable power source for conformable bioelectronics, offer high-power density, flexibility, and longevity. Conducting polymer hydrogels (CPHs) combine electronic conductivity and mechanical flexibility, making them promising electrode materials for seamless interfacing with biological tissues. Nevertheless, most pristine CPHs are brittle and crack under deformation, sacrificing device performance. Herein, a fully conductive, biocompatible, and mechanically robust 3D polypyrrole (PPy)-Ti₃C₂T_x hydrogel (PMCH) is reported to overcome these challenges in wearable supercapacitors. A multi-step gelation mechanism wherein Ti₃C₂T_x nanosheets (NSs) are fine-tuned as conductive cross-linkers for PPy chains is utilized, endowing structural elasticity to the PMCH. The hierarchical, water-saturated mesopores guaranteed an ion-rich hydrophilic environment, boosting access to redox-active sites. Consequently, the PMCH-3 (only 33.33 wt.% Ti₃C₂T_x NSs) delivered a striking specific capacitance of 368.3 F g^-1 in an expanded potential window of 1 V. As a proof-of-concept, the all-gel solid-state supercapacitor with commercially-relevant mass loading successfully powered a red LED under bending and retained 92.1% of its capacitance across 1000 bending cycles, showcasing excellent wearability. The lightweight, affordable device delivered a state-of-the-art energy density of 49.8 µWh cm^-2 and a peak power density of 8000 µW cm^-2, meeting the rigorous demands of next-generation wearable electronics.