Unveiling Local\nAtomic Ordering of Nb<sub>α</sub>V<sub>2‑α</sub>CT<sub><i>x</i></sub> MXenes\nfor Lithium-Ion Storage

The\ndemand for innovative materials in energy storage\nand generation\nnecessitates precise atomic-scale chemical control in nanomaterials.\nDouble-transition metal (DTM) MXenes have expanded the chemical diversity\nof layered 2D materials, exhibiting unique physicochemical properties.\nHowever, the atomic ordering of DTMs and its impact on lithium storage\nperformance require further investigation. Here, we report the synthesis\nof two-dimensional niobium–vanadium carbides (Nb<sub>α</sub>V<sub>2‑α</sub>CT<sub><i>x</i></sub>) by Lewis\nacid etching strategy, a previously unexplored class of DTM MXenes.\nBy utilizing X-ray absorption fine structure (XAFS) spectra, we demonstrate\nthat adjusting the Nb/V ratio enables tuning of the coordination number\nof Nb/V in Nb<sub>α</sub>V<sub>2‑α</sub>CT<sub><i>x</i></sub>. As a result, the resulting Nb<sub>1.4</sub>V<sub>0.6</sub>CT<sub><i>x</i></sub> with enhanced local\natomic ordering exhibited excellent rate performance and remarkable\ncycling stability. This study highlights the atomic-scale characterization\nof local structures using advanced X-ray spectroscopic techniques,\nexpanding the diversity of the MXenes family.