By first-principles calculation and experimental measurements, we investigated the lithiation process in the Ti4C3 and Ti2Ta2C3 MXenes. Our results show the successful synthesis of the Ti2Ta2C3 MXene with an interlayer distance of 0.4 nm, which supposes the correct delamination of the material. Our measurements also demonstrate that the double-ordered alloy Ti2Ta2C3 can store 4 times the amount of lithium than the pristine Ti4C3 MXene. By DFT calculation, we investigated the stability of the Ti x Ta4–x C3 MXenes. According to the calculations, five MXenes are stable, where the most stable 50% Ta/Ti ratio structure (Ti2Ta2C3) presents a chemically ordered composition. The Li intercalation processfor Ti4C3 and Ti2Ta2C3 MXenesis carried out as adatoms on the surface, with the T4 site being the most favorable. The chemically ordered MXenes provide better OCV values and can store more Li atoms than the Ti4C3 MXene. Also, the Li diffusion process demonstrates that Ti2Ta2C3 is a more efficient material to be employed as an anode in batteries since it provides the lowest energy barriers. Our results demonstrate the capability of the Ti2Ta2C3 alloy to be employed in energy storage applications thanks to the high stability and capacity to store Li ions in comparison with pristine Ti4C3 MXene.

Using DFT calculations, we investigated the structural, electronic, and magnetic properties of the Cr2N MXene functionalized with different oxygen concentrations. Our calculations show that pristine Cr2N shows an antiferromagnetic (AFM) behavior; also, according to the density of states, the MXene is metallic, in agreement with previous reports. We study the changes in the magnetic and electronic properties of the functionalized Cr2NO x MXene with 1 < x ≤ 2; in all cases, O occupies the H3 site; in the range 0.25 < x ≤ 0.75, the system acquires half-metallic properties with ferrimagnetic alignments. In the range 1 < x ≤ 1.75, the MXene returns to be metallic; also, the FiM characteristic remains. Finally, for full oxygen coverage, the functionalized MXene switches to the ferromagnetic state with half-metallic properties, which match with the results previously reported by Wang and Kumar et al. Pristine CrN exhibits an energy difference of ∼1.5 eV between AFM and FM, and this energy difference starts to decrease as the oxygen concentration increases. For the Cr2NO MXene, the difference is ∼0.75 eV, and for a fully oxidized MXene, the most stable configuration is FM. Our results suggest that the AFM to FM transition is a gradual process, where the oxygen concentration plays an essential role in the magnetic properties of the MXene. Our calculations demonstrate that the Cr2NO x MXene at different oxygen coverages is suitable for spintronic applications as by varying the oxygen coverages, we can modulate the spin polarization around the Fermi level.

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