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

Abstract

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 Tc 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 Tc 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 Tc for Ti2CHx, 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.