Role of Oxygen and Halogen Functionalization in Tuning the Surface Properties of ZrCT MXene for Lithium Storage: A Density Functional Theory Study.

We constructed computational models of bare ZrC and surface-functionalized ZrCT (T = O, S, F, Cl), and utilized first-principles calculations to systematically explore the effects of these surface-functionalized groups on the structural stability, electronic properties, and lithium storage performance of ZrCT. Compared to halogen functional groups (e.g., F, Cl), the structure and electronic properties of ZrC are more profoundly influenced by oxygen group functional elements (O, S). The formation energy of ZrCT (T = O, S) functionalized by the same periodic oxygen group elements is lower than that of ZrCT (T = F, Cl) functionalized by the same periodic halogens. Regarding electronic properties, the oxygen and sulfur functional groups have strong hybridization with ZrC in the valence band and generate a new band structure, which makes the DOS move toward the conduction band. The adsorption energy calculations reveal that lithium ions exhibit stable adsorption on bare ZrC and O/S-functionalized ZrCT surfaces, whereas no stable adsorption occurs on ZrCF or ZrCCl. In terms of adsorbing lithium atoms, bare ZrC tends to adsorb at the HCP position, while ZrCO and ZrCS tend to adsorb at the CCP position. First-principles calculations indicate distinct theoretical lithium storage capacities for ZrC-based materials: monolayer adsorption yields capacities of 180.13 mAh/g (bare ZrC), 162.64 mAh/g (ZrCO), and 148.20 mAh/g (ZrCS); bilayer adsorption significantly increases these values to 360.25, 325.29, and 296.41 mAh/g, respectively.