Hydrogen-induced phase stability and phonon mediated-superconductivity in two-dimensional van der Waals Ti2C MXene monolayer

Herein, we report the phase stability of the hydrogenated Ti₂C MXene monolayer using an evolutionary algorithm based on density functional theory. We predict the existence of hexagonal Ti₂CH, Ti₂CH₂, and Ti₂CH₄. The dynamic and energetic stabilities of the predicted structures are verified through phonon dispersion and formation energy, respectively. The electron-phonon coupling is carefully investigated by employing isotropic Eliashberg theory. The T_c values are 0.2 K, 2.3 K, and 9.0 K for Ti₂CH, Ti₂CH₂, and Ti₂CH₄, respectively. The translation and libration adopted by stretch and bent vibrations contribute to the increasing T_c of Ti₂CH₄. The high-frequency hydrogen modes contribute to the critical temperature increase. Briefly, this work not only highlights the effect of H-content on the increments of T_c for Ti₂CH_x, but also demonstrates the first theoretical evidence of the existence of H-rich MXene in the example of Ti₂CH₄. Therefore, it potentially provides a guideline for developing hydrogenated 2D superconductive applications.