Defect Engineering and Effect of Vacancy Concentration on the Electrochemical Performance of V‐Based MXenes

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Vacancies play a pivotal role in determining the physical and chemical properties of materials. Introducing vacancies into two‐dimensional (2D) materials offers a promising strategy for developing high‐performance electrode materials for electrochemical energy storage. Herein, a facile top‐down strategy is employed to create V‐based MXenes with tunable vacancy concentrations, achieved by designing the precursor (V 1−x Cr x ) 2 AlC (x = 0.05, 0.1, 0.3) MAX phase and precisely controlling the etching process. Systematic investigations reveal that introducing a moderate concentration of Cr‐induced vacancies significantly enhances both the capacitance and rate performance of V‐based MXenes. Specifically, V 1.9 CT z achieves a capacitance of 760 F g −1 , far exceeding the 420 F g −1 of vacancy‐free V 2 CT z MXene. In contrast, an excessively high vacancy concentration leads to deteriorated electrochemical performance and compromised structural stability. This work illustrates that defect engineering is a powerful approach to tailor the electrochemical properties of MXenes, offering a framework for designing next‐generation MXene‐based energy storage systems.