Electronic Delocalization-Confinement Coupling in Edge-Coordinated CQDs@MXene Enables Hydrogen-Bond Modulation for Ultrafast Proton Transport.

Abstract

Efficient proton transport in 2D confined electrodes critically depends on the flexibility of interfacial hydrogen-bond networks. However, the interfacial issue becomes more pronounced in the 2D confined space. The strong hydrogen bonds between confined water molecules and surface ─O terminations of MXenes immobilize protons and hinder charge storage kinetics. Here, we introduce an edge-coordination strategy to achieve precise electronic delocalization modulation in Ti₃C₂T_x MXene by anchoring carboxyl-functionalized carbon quantum dots (CQDs) at positively charged edges. The CQDs induce substantial electron delocalization on surface ─O sites, which simultaneously weakens rigid hydrogen bonds and facilitates interfacial charge transfer. This regulation establishes a dynamic hydrogen-bond network that supports continuous Grotthuss-type proton migration within the confined channels. Consequently, the optimized CQDs@MXene electrode delivers a volumetric capacitance of 2507.2 F cm^-3, retains 65.8% at 1000 mV s^-1, and maintains nearly 100% stability over 10 000 cycles. In situ vibrational spectroscopy and density functional theory reveal that the electron delocalization drives the weak hydrogen-bond interface and charge transfer coupling governs proton transport kinetics. This work establishes electronic delocalization as an effective paradigm for manipulating hydrogen-bond dynamics and interfacial charge transport for ultrafast ion transport in confined electrochemical systems.