Boosting sodium hybrid-ion capacitor performance via exfoliated Ti3C2TX (O/OH/F) anode and bio-derived activated hard carbon cathode

The exfoliated MXene (eTCT) was synthesized from its parent MAX phase using a hydrofluoric acid-free etching system (HCl/LiF). The resulting eTCT sample exhibits a specific surface area of 51 m 2 g −1 The fabricated eTCT electrode demonstrates remarkable electrochemical performance, delivering a high gravimetric specific discharge capacity of ∼280 mAh g −1 and an impressive specific capacitance of ∼385 F g −1 , along with excellent rate capability. Cyclic voltammetry measurements reveal maximum specific capacitances of ∼730 F g −1 and ∼ 418 F g −1 at scan rates of 0.1 mV/s and 0.5 mV/s, respectively. After 150 cycles, the eTCT cell retains approximately 70 % of its initial discharge capacity, corresponding to a capacity fade rate of only 0.2 % per cycle. For energy storage applications. Further MXene's potential is explored by fabricating a sodium hybrid-ion capacitor (SHIC). Based on the total active mass of both electrodes, the SHIC achieves a gravimetric specific capacitance of 79 Fg −1 . The eTCT//AMHC system demonstrates outstanding power and energy densities reaching ∼4.1 kW k g −1 and 156 Wh k g −1 , respectively. These values surpass many lithium-based capacitors, highlighting the superior performance of MXene-based devices. The Wien2k calculations reveal that LiF-etched MXene exhibits enhanced electronic conductivity. Notably, MXene ( F, -OH, O) show higher density of states (DOS) near the Fermi level compared to MAX phase, suggesting the enhancement in metallic character of MXene. Furthermore, the strong Na O interaction in Ti 3 C 2 O 2 makes it particularly promising for sodium-ion storage applications. • HF-free etching of MXene (Ti 3 C 2 T x ) using HCl/LiF ensures safer synthesis compared to traditional HF methods. • The BET surface area of the exfoliated MXene was found to be approximately 51 m 2 g −1 . • Exfoliated MXene (eTCT) delivers 280 mAh g −1 capacity and 385 F g −1 capacitance in NaClO 4 electrolyte. • Sodium hybrid-ion capacitor (SHIC) achieves 156 Wh kg −1 energy density and 4.1 kW kg −1 power density . • Wien2k simulations confirm enhanced conductivity in -O/-OH terminated MXene over F termination.