A nitrogenous pre-intercalation strategy for the synthesis of nitrogen-doped Ti3C2Tx MXene with enhanced electrochemical capacitance

Abstract

Tremendous efforts have been dedicated towards high-performance energy storage devices though material innovation, nanoscale structural design and hybrid fabrication approaches. A crucial technique to tune the properties of nanomaterials, such as MXene, is through introducing defects or heteroatom dopants. To improve the level of nitrogen dopant, a two-step pre-intercalation–annealing strategy is developed herein, using ammonium citrate (AC) as an all-in-one intercalant, antioxidant and nitrogen source, followed by annealing in an ammonia atmosphere. It is shown that the doping efficiency of nitrogen-doped Ti₃C₂T_x MXene (N-MXene) increased from 3.5% to 6.3%, compared with MXene annealed in ammonia without pre-intercalation. This high doping level induces significantly enhanced electrochemical capacitance (475 F g⁻¹ at 5 mV s⁻¹) compared with pristine MXene (321 F g⁻¹), and greatly improved performance at high current density (248 F g⁻¹ at 1 V s⁻¹). Modelling was performed to elucidate the N-doping process of MXene and to understand the mechanism enhancing the electrochemical capacitance, which indicates that the pre-intercalation strategy promotes N-doping as surface functionalization, as well as in the MXene lattice. The pre-intercalation strategy demonstrates a new and facile pathway for functionalizing Ti₃C₂T_x MXene which will facilitate use in applications such as in high performance supercapacitors.