  Finding a suitable material for hydrogen storage at ambient atmospheric
conditions is challenging for material scientists and chemists. In this work,
using a first principles based cluster expansion approach, the hydrogen storage
capacity of Ti2AC (A = Al,Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn) MAX phase and its
alloys were studied. We found that hydrogen is energetically stable in Ti-A
layers in which the tetrahedral site consisting of one A atom and three Ti
atoms is energetically more favorable for hydrogen adsorption than other sites
in the Ti-A layer. Ti2CuC has the highest hydrogen adsorption energy than other
Ti2AC phases. We find that 83.33% Cu doped Ti2AlxCu1-xC alloy structure is both
energetically and dynamically stable and can store 3.66 wt% hydrogen at ambient
atmospheric conditions, which is higher than both Ti2AlC and Ti2CuC phase.
These findings indicate that the hydrogen capacity of the MAX phase can be
significantly improved by doping an appropriate atom species.
