Self-assembled S,N co-doped reduced graphene oxide/MXene aerogel for both symmetric liquid- and all-solid-state supercapacitors

Two-dimensional (2D) transition metal carbon/nitrogen compound (MXene) and graphene are popular energy storage materials. Still, the electrochemical performance and application of those 2D materials are severely limited due to their easy self-stacking. In this article, three-dimensional (3D) hybrid porous aerogel made of sulfur and nitrogen doped reduced graphene oxide and MXene (S,N-rGO@MXene) is successfully self-assembled via a simple hydrothermal method. The reductive nature of MXene positively tune the hydrophilicity of rGO, thus leading to a controllable formation of 3D mutual cross-linking rGO/MXene. The involvement of elemental S and N additionally promotes electrochemical performance. The specific capacitances of 85.4 and 88.9 F g-1 in symmetric liquid- and all-solid-state supercapacitors assembled with S,N-rGO@MXene are achieved at the current density of 1 A g-1, respectively. Notably, the capacitance retention and Coulombic efficiency remain almost unchanged after 20,000 and 10,000 charge/discharge cycles in the respective systems. In particular, the all-solidstate supercapacitor achieves a high energy density of 24.2 Wh kg- 1 at the power density of 1400.6 W kg- 1, outperforming most of the MXene-based all-solid-state supercapacitors reported so far. Practically, the