Built‐In Interfacial Electric Field in Hydroxyl‐Terminated MXene/COF Heterostructures for Enhanced Solid‐State Supercapacitors

ABSTRACT Engineering heterointerfaces that enable fast and coordinated ion‐electron transport is a central challenge for high‐performance solid‐state supercapacitors. Herein, a termination‐engineered strategy is reported to construct MXene/COF heterostructures with a built‐in interfacial electric‐field effect by regulating MXene surface chemistry. Fluorine‐terminated Ti 3 C 2 F 2 MXene is converted into hydroxyl‐rich Ti 3 C 2 (OH) 2 via tetrabutylammonium hydroxide (TBAOH) treatment, enhancing surface reactivity and interlayer accessibility. The hydroxyl‐terminated MXene is subsequently integrated with a redox‐active diaminoanthraquinone‐based covalent organic framework (DAAQ‐COF) through electrostatic self‐assembly followed by hydrothermal treatment, yielding conformally anchored COF nanoneedles on MXene sheets. The resulting heterointerface promotes interfacial charge redistribution, accelerated charge‐transfer kinetics, and improved ion accessibility. The optimized Ti 3 C 2 (OH) 2 /DAAQ‐COF (1:1) hybrid delivers a high specific capacitance of 390.97 F g −1 at 0.5 A g −1 with 99% retention over 20000 cycles. An all‐solid‐state symmetric supercapacitor achieves 17.75 Wh kg −1 at 230.8 W kg −1 and retains 86.8% capacity after prolonged cycling. Combined experimental analyses and density functional theory calculations indicate that hydroxyl termination induces favorable interfacial charge redistribution and band alignment, giving rise to an interfacial electric‐field effect that facilitates fast electron transport and efficient ion diffusion. This work reveals MXene surface termination as a key factor regulating interfacial electric fields and ion‐electron transport in MXene/COF heterostructures.