First-principles study of hydrogen incorporation into the MAX phase Ti3AlC2

Abstract

First-principles calculations have been performed to study hydrogen incorporation into the MAX phase Ti3AlC2. It is found that H atoms are thermally favorable to be incorporated into the interstitial sites of Ti-Al layers in stoichiometric Ti3AlC2. Only when C vacancies exist, H atoms can be incorporated into Ti-C layers. In Ti-Al layers, the hexagonal interstitial site (Ihexa) consisting of three Al atoms and two Ti atoms, the tetrahedral interstitial site (Itetr-2) consisting of one Al atom and three Ti atoms, and the octahedral interstitial site (Ioct-3) consisting of three Ti atoms and three Al atoms are all possible sites for H incorporation. Among them, Itetr-2 is the most stable one, followed by Ioct-3, and the last one is Ihexa sites. The linear synchronous transit optimization study shows that the diffusion of H in the Ti-Al layers is feasible which could be helpful for the continuous insertion and the following extraction of H in Ti3AlC2.