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

Abstract

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 m2 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 ([sbnd]F, -OH, [sbnd]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[sbnd]O interaction in Ti<inf>3</inf>C<inf>2</inf>O<inf>2</inf> makes it particularly promising for sodium-ion storage applications. © 2025