Hydrothermal direct synthesis of polyaniline, graphene/polyaniline and N-doped graphene/polyaniline hydrogels for high performance flexible supercapacitors

Abstract

Electroactive hydrogels have been considered as flexible solid-state supercapacitor electrode materials. Herein, a novel strategy has been proposed to directly prepare polyaniline (PANI) hydrogels from soluble PANI dispersion by self-crosslinking of molecules during the hydrothermal process. The PANI hydrogel single-electrode shows high specific capacitance (325 F g⁻¹) and superior rate capability. To achieve more excellent electrochemical performance, the graphene/PANI hydrogel (GPH7) is prepared using graphene oxide (GO) and soluble PANI dispersion. However, a slightly enhanced specific capacitance (375 F g⁻¹) is achieved for the GPH7 single-electrode, due to the strong interactions between GO and PANI molecules. It is of particular interest that the incorporation of m-phenylenediamine (mPD) into the GO and PANI system could protect the inherent conjugated structure of PANI, and thereby the as-prepared N-doped graphene/PANI hydrogels (GMPH7) show significantly improved specific capacitance (514.3 F g⁻¹). Moreover, the assembled flexible solid-state supercapacitors based on the PANI hydrogel, GPH7 and GMPH7 exhibit excellent areal specific capacitance (484, 519.2 and 584.7 mF cm⁻², respectively), approximately 100% capacitance retention after 2000 mechanical bending cycles and favorable energy density (42.96, 60.9 and 81.28 μW h cm⁻², respectively). Such hydrogel assembled supercapacitors with robust capacitive behavior and outstanding flexibility are promising for applications in flexible and wearable electronics.