First-principles study of hydrogen adsorption behavior in C15 Laves phase compound ZrV2

Abstract

The hydrogen absorption behavior of C15 Laves phase compounds ZrV2 has been systematically investigated by the first-principles calculations. In the C15 Laves phase, hydrogen atoms can occupy three possible tetrahedral interstitial positions - 2A2B, 1A3B, and 4B - in which the 2A2B site, being the largest interstitial space among the three possible positions, is the most favorable interstitial site. In addition, 2A2B and 1A3B sites can form some ordered clathrate-type structures to provide diffusion paths for hydrogen atoms to move inside the ZrV2 compounds. According to the calculated barrier energies of H atoms in different diffusion paths in ZrV2, it is found that hydrogen atoms prefer intra-ring diffusion to inter-ring diffusion, although inter-ring diffusion provides a non-negligible contribution to the overall H diffusion process. However, the existence of 1A3B sites can facilitate the diffusion of hydrogen atoms in adjacent six-membered rings. Finally, the absorption energies and electronic structures of ZrV2Hx (x = 0.5, 1, 2, 3, 4, 6, 7, and 12) were computed, and the results show that the hydrogen content reaches its maximum on the condition of 6 < x < 7. Moreover, hydrogen atoms make a stronger covalent bond with V atoms than with Zr atoms.