In Situ Nitrogen Functionalization of 2D-Ti₃C₂T-MXenes for High-Performance Zn-Ion Supercapacitor

Zinc (Zn) ion supercapacitors (ZISCs) have attracted considerable attention as a viable energy storage technology because they are cost-effective, safe, and environmentally friendly. However, cathode materials with suitable properties are rare and need to be explored. In this regard, metal carbides (MXenes) are a good choice for capacitive energy storage, but they exhibit low capacitance. The energy storage performance of MXenes can be bossed using functionalization with heteroatom doping, e.g., nitrogen (N), to simultaneously modify ZISCs' fundamental characteristics and electrochemical properties. Herein, we present an in-situ N-functionalization of Ti₃C₂T-MXene via a hydrothermal reaction with urea (denoted as N-Ti₃C₂T-MXene). N-functionalization into Ti₃C₂T-MXene raised Ti₃C₂T-MXene's interlayer spacing and boosted the Zn-ion storage in 1 M ZnSO₄ electrolyte. The N-Ti₃C₂T-MXene electrode delivered an excellent specific capacitance of 582.96 F/g at 1 A/g and retained an outstanding cycle stability of 94.62% after 5000 cycles at 10 A/g, which is 1.8 times higher than pristine Ti₃C₂T-MXene at identical conditions. Moreover, the N-Ti₃C₂T-MXene//Zn device demonstrated a maximum capacitance of 153.55 F/g at 1 A/g, retained 92% of its initial value after 5000 cycles, and its Coulombic efficiency was ~100%. This strategy considerably reduced Ti₃C₂T-MXene nanosheet restacking and aggregation and enhanced electrochemical performance. Further, this research elucidated N-Ti₃C₂T-MXene's charge-storage process and offered a fresh approach to the rational design of novel electrode materials for ZISCs.