A Flexible Supercapacitor Based on Niobium Carbide MXene and Sodium Anthraquinone-2-Sulfonate Composite Electrode

MXene-based composites have been widely used in electric energy storage device. As a member of MXene, niobium carbide (Nb₂C) is a good electrode candidate for energy storage because of its high specific surface area and electronic conductivity. However, a pure Nb₂C MXene electrode exhibits limited supercapacitive performance due to its easy stacking. Herein, sodium anthraquinone-2-sulfonate (AQS) with high redox reactivity was employed as a tailor to enhance the accessibility of ions and electrolyte and enhance the capacitance performance of Nb₂C MXene. The resulting Nb₂C-AQS composite had three-dimensional porous layered structures. The supercapacitors (SCs) based on the Nb₂C-AQS composite exhibited a considerably higher electrochemical capacitance (36.3 mF cm^-2) than the pure Nb₂C electrode (16.8 mF cm^-2) at a scan rate of 20 mV s^-1. The SCs also exhibited excellent flexibility as deduced from the almost unchanged capacitance values after being subjected to bending. A capacitance retention of 99.5% after 600 cycles was observed for the resulting SCs, indicating their good cycling stability. This work proposes a surface modification method for Nb₂C MXene and facilitates the development of high-performance SCs.