Boosting Ion Transport in MXene Films via In-Plane Nanopores and Embedded TiO₂ Nanoparticles: Toward Ultrafast...

Two-dimensional MXene (Ti₃C₂T_x) is a promising electrode material for ultrafast supercapacitors (SCs) owing to its high specific surface area and metallic conductivity. However, the performance is fundamentally limited by sluggish ion transport kinetics, which originates from two intertwined structural issues: the inherently high tortuosity (τ) of ion pathways within restacked nanosheets and the limited accessibility of internal active sites. Herein, we design and fabricate a TiO₂-embedded holey Ti₃C₂T_x (TiO₂/H-Ti₃C₂T_x) film electrode via a simple hydrothermal H₂O₂ treatment followed by vacuum filtration. This design implements a dual-mechanism strategy: the creation of in-plane nanopores provides vertical shortcuts for rapid ion diffusion, while the in-situ grown TiO₂ nanoparticles act as structural pillars to widen interlayer spacing and prevent restacking, thereby synergistically reducing ion transport tortuosity and exposing abundant ion-accessible active sites. As a direct consequence of this structural engineering, the assembled SC achieves exceptional frequency performance, delivering high areal and volumetric capacitances of 1164 µF cm^-2 and 14.9 F cm^-3 at 120 Hz with a phase angle of -80°. This performance surpasses most reported pseudocapacitive filter SCs and commercial aluminum electrolytic capacitors. Its practicality is demonstrated by effective high-frequency AC-line ripple smoothing, highlighting the material's promise for powering next-generation miniaturized electronics.