Efficient electrochemical performance of asymmetric supercapacitor based on nitrogen-doped Nb₂CT_x MXene in an alkaline electrolyte

The versatile, and tunable surface chemistry of two-dimensional (2D) MXenes coupled with their distinct properties including hydrophilic nature, favorable ion transport and metallic conductivity make them an ideal candidate for energy storage devices. Modifying surface terminations by doping heteroatom is an efficient approach to improve layer spacing and electrochemical active sites of the MXenes. However, nitrogen doping in 2D materials has been an effective way to enhance their electrochemical characteristics. In this study, N-Nb₂CT_x MXene was synthesized by utilizing the hydrothermal method in which nitrogen doping in MXene was confirmed through several characterization techniques. Tuning of MXene surface by a cost-effective strategy has shown improved performance for energy storage. After doping nitrogen in Nb₂CT_x MXene, it has shown enhanced pseudocapacitance performance in 1 M potassium hydroxide (KOH), elevating the electrochemical properties. N-Nb₂CT_x MXene has displayed a better specific capacitance of up to 640 F·g^–1 while pristine Nb₂CT_x MXene has shown 276 F·g^–1 from the cyclic voltammogram (CV) at a scan rate of 5 mV·s^–1. In addition, an asymmetric device of activated carbon/N-Nb₂CT_x was assembled for real-world applications, it has exhibited refined results. The asymmetric device has shown remarkable cyclic stability of 90% capacity retention at a current density of 5 A·g^–1 for 5000 cycles. Additionally, the detailed density functional theory (DFT) calculations support the stability of nitrogen replacing the fluorine functional group, complementing the experiment.