Lewis acid-etched MXene self-assembled with reduced graphene oxide for symmetrical supercapacitors with liquid/ solid electrolytes

Two-dimensional graphene and metal carbide/nitride/carbonitride compounds (MXene) are widely recognized as promising electrode materials for electrochemical energy storage systems. Herein, MXene was hydrothermally self-assembled with graphene oxide to form three-dimensional porous aerogels, which were applied as electrode materials in symmetrical supercapacitors with both liquid and solid electrolytes. The fabricated supercapacitors exhibited excellent supercapacitive performances including superior capability, coulombic efficiency, and cycle stability. The specific capacitance of the aerogel-based supercapacitor assembled with liquid KOH electrolyte reached as high as 158.6 F g−1, while the fabricated all-solid-state supercapacitor displayed a power density of 1398.8 W kg−1 and an energy density of 33.3 Wh kg−1 at a current density of 1 A g−1. Notably, MXene was prepared via a more enviromentally friendly route by using molten Lewis acid instead of the traditional fluorine-involved agent as the etchant, thus efficiently limiting the hazardous chemicals to pollute the environment. This work provides a strong motivation for applying graphene and MXene composite materials in sustainable energy storage systems.