Surface-engineered Ti₃C₂T _xMXene enabling rapid sodium/potassium ion storage

MXene with expanding interlayer and tunable terminations emerge as promising candidates for metal ion storage. Herein, we develop a facile urea decomposition strategy to obtain ultrathin nitrogen-modified Ti3C2T x (N-UT-Ti3C2T x ) with optimized terminations as anode for sodium/potassium ion storage. Experimental results have shown that NH3 molecules produced by urea pyrolysis could introduce two types of nitrogen modifications in Ti3C2, function substitution for -OH (FS) and surface absorption on -O (SA). During subsequent hydrothermal and heating processes, the nitrogen atoms in situ substitute the lattice carbon in Ti3C2 (LS). Further, the effects of these nitrogen modifications in Ti3C2 on diffusion kinetics of Na+ and K+ are investigated by first-principles calculations. The superior Na+ storage performances of the N-UT-Ti3C2T x anode are the main attribute of the nitrogen modification of LS in Ti3C2, while the excellent K+ storage performances come from the synergistic effects of the nitrogen modifications of FS and LS in Ti3C2. This work emphasizes the effectiveness of surface engineering of nitrogen modifications and optimized terminations for improving the electrochemical performances of Ti3C2T x and inspires the design of heteroatom modified MXenes for energy storage.