Thermally modulated dual-heteroatom (S,P) doping of Ti₃C₂Tₓ MXene toward advanced symmetric supercapacitors

Abstract

Supercapacitors (SCs) have attracted considerable interest owing to their high-power density, rapid charge/discharge capability, exceptional cycle stability, and resilience under challenging conditions. Ti 3 C 2 T x MXene, a two-dimensional material, has demonstrated significant promise as an electrode material for electrochemical energy storage; However, its low specific capacitance, imposed by self-restacking of the interlayers, nevertheless restricts its potential applications. Herein, a simple heteroatom approach is proposed for generating Ti 3 C 2 T x MXene with a substantial active site content through single and double doping with sulfur (S) and phosphorus (P) over different temperature ranges. Ti 3 C 2 T x MXene was accordingly produced by a (LiF+HCl) etching technique, whereas a simple annealing method was employed to synthesize S-doped Ti 3 C 2 T x MXene, P-doped Ti 3 C 2 T x MXene, and SP-doped Ti 3 C 2 T x MXene at three different temperatures (250 °C, 500 °C, and 750 °C). Physical investigation of the materials was conducted using XRD, SEM, EDX, TEM, FTIR, BET, Raman, TG/DTA, and XPS protocols. Capacitance efficiency was assessed in a three-electrode setup using 1 M H 2 SO 4 electrolyte, with emphasis placed on electrochemical investigation by CV, GCD, and EIS. The electrochemical analysis by GCD revealed that the SP-doped Ti 3 C 2 T x MXene sample prepared at 750 °C delivered the ultimate specific capacitance of 177.66 F g⁻¹ at a current density of 0.5 A g⁻¹ relative to the other five electrodes, namely bare Ti 3 C 2 T x MXene, S-doped Ti 3 C 2 T x MXene, P-doped Ti 3 C 2 T x MXene, and SP-doped Ti 3 C 2 T x MXene obtained at 250 °C and 500 °C. The formulated SP-doped Ti 3 C 2 T x MXene at 750 °C was therefore utilized as an SC electrode material. The electrode further demonstrated a remarkable energy density of 9.18 Wh.kg⁻¹ at a power density of 150 W. kg⁻¹. The SP-doped Ti 3 C 2 T x MXene at 750 °C exhibited an exceptional capacitance retention of ≈100% at 10 A g⁻¹, along with significant cycling stability over 5000 continuous cycles.