Multifunctional enhanced energy density of flexible wide-temperature supercapacitors based on MXene/PANI conductive hydrogel

Conducting polymer-based conductive hydrogels can offer adjustable electronic characteristics and superior mechanical performance, thus holding significant promise for flexible supercapacitors. However, some of such hydrogel electrodes still suffer from inferior stability, unsatisfactory energy density, and narrow temperature tolerance, which limit their widespread use in flexible supercapacitors. Herein, polyaniline was coated on the surface of Ti3C2Tx MXene flakes by in-situ chemical oxidative polymerization of aniline monomer pre-assembled on the MXene surface. The resulting MXene/PANI conductive nanofillers, Fe3+ ions, and phytic acid were introduced into the gelatin/polyacrylamide hydrogel scaffold to form highly stretchable MPGP-Fey hydrogel electrodes. Benefiting from the highly electrochemical activity of MXene/PANI conductive nanocomposite, efficient redox transition of Fe3+/Fe2+, and high open structure, the assembled all-gel symmetrical MPGP-Fey supercapacitors can achieve a maximum specific capacitance of 847 mF/cm2, an impressive energy density of 71.8 μWh/cm2, and an exceptional cyclic stability, retaining 95 % capacitance retention after 5000 cycles. The phytic acid is advantageous in lowering the freezing points of both the hydrogel electrode and electrolyte layer. The developed supercapacitors demonstrate promising temperature-adaptive properties over a wide range of −30 ∼ 90 °C. When operated at −30 °C, an impressive stable output with long-term stability of 93 % retention are achieved. With the merits of good processability, high flexibility and stretchability, the present device can serve as an optimal energy source for powering diverse electronic components in practical applications.