Functionalization-driven modulation of electronic structure and quantum capacitance in o-MXene Y₂VC₂T_x (T_x = O₂, F₂,...

In this study, first-principles calculations based on density functional theory (DFT) combined with the pseudopotential method are employed to investigate and compare the electronic properties, structural stability, and energy-storage potential of novel two-dimensional binary transition metal systems, Y₂VC₂T_x (T_x = O₂, F₂, and OF) o-MXenes. Structural, mechanical, and dynamical analyses confirm the potential stability of all Y₂VC₂T_x o-MXenes. Among them, the oxygen-terminated Y₂VC₂O₂ layer exhibits superior energetic and mechanical stability compared to the pristine Y₂VC₂, fluorinated Y₂VC₂F₂, and mixed-functionalized Y₂VC₂OF structures. The calculated B/G ratios for Y₂VC₂, Y₂VC₂F₂, Y₂VC₂O₂, and Y₂VC₂OF are above 1.75, indicating ductile mechanical characteristics in these systems. Electronic structure analyses conducted using different exchange-correlation schemes (GGA and GGA+HSE06) reveal that the studied o-MXenes behave metallically within the GGA approximation, while under the GGA+HSE06 functional, the materials Y₂VC₂, Y₂VC₂F₂, Y₂VC₂OF, and Y₂VC₂O₂ exhibit energy gaps of 1.62, 2.94, 2.27, and 2.48 eV, respectively, confirming their semiconducting nature. The pseudogap positioned closer to the Fermi level in Y₂VC₂O₂ implies higher electronic robustness compared to other variants. In aqueous media, oxygen-terminated surfaces exhibit the strongest electrochemical activity, while pristine Y₂VC₂ shows the weakest response. Y₂VC₂O₂ and Y₂VC₂OF consistently function as anodic electrodes, whereas Y₂VC₂ and Y₂VC₂F₂ act as cathodic electrodes under aqueous conditions. In ionic/organic environments, Y₂VC₂, Y₂VC₂O₂, and Y₂VC₂OF maintain anodic behavior, while Y₂VC₂F₂ remains cathodic. Moreover, Y₂VC₂O₂ demonstrates remarkable quantum capacitance and highly tunable electrochemical performance, largely driven by surface functionalization. These enhancements significantly improve the energy-storage capabilities of the materials, positioning o-MXenes as strong candidates for next-generation supercapacitors and battery electrodes.