Interfacial Dirac‐Modulated TiN/MXene Heterostructure Enables Decoupled Ion‐Electron Transport for Ultrafast Ammonium‐Ion Storage

Abstract Aqueous ammonium‐ion hybrid pseudocapacitors (AAI‐HPCs) demand anodes that unify metallic conductivity, ultrafast NH 4 + kinetics, and robust cycling, a feat unattainable with conventional 2D materials due to irreversible restacking, necessitating atomic‐precision heterostructure design. Herein, in situ nitrogen‐engineered TiN/MXene cascades are developed through hexamine‐derived NH 3 nitridation, inducing spontaneous N‐vacancy formation and epitaxial TiN nucleation, simultaneously preventing MXene restacking while creating expanded ion diffusion highways. Polyvinylpyrrolidone (PVP)‐directed interfacial confinement precisely integrates ultrathin Ag‐Bi 2 Te 3 nanoplates into the TiN/MXene matrix, where topological Dirac states ensure metallic conductivity while enhancing mechanical robustness. The resulting Ag‐Bi 2 Te 3 @TiN/MXene heterostructure establishes dual hydrogen‐bonded NH 4 + coordination sites, combining stable Ti─N─H─N anchoring with Ag‐enhanced Te─H─N interactions, collectively reducing diffusion barriers by 33.3% (from 36 to 24 eV). Ex‐situ/operando analysis confirms reversible Bi 3+ /Bi 0 and Ag + /Ag 0 redox couples operating in concert with strain‐adaptive MXene frameworks, achieving exceptional 98.1% capacity retention over 5,000 cycles. Full‐cell Ag‐Bi 2 Te 3 @TiN/MXene//AC (AAI‐HPCs) deliver record energy density 79.2 Wh kg −1 (at 800 W kg −1 ) capable of powering commercial electronics for >100 s, with flexible pouch cells reaching 96.5 Wh kg −1 under mechanical stress—surpassing reported MXene‐based NH 4 + systems. This work establishes interfacial electron modulation as a universal design paradigm for decoupled ion‐electron transport in next‐generation AAI‐HPCs.