Hydrogen absorption in Ti–Zr–Ni quasicrystals and 1/1 approximants

Abstract

Ti/Zr-based quasicrystals and their approximants draw attention as new candidate materials for hydrogen storage applications based on recent discoveries that they absorb a large amount of hydrogen, reversibly, at low temperatures and pressures. In fact, Ti 45Zr 38Ni 17 quasicrystals take hydrogen to a maximum value of hydrogen to host metal atom ratio (H/M) of nearly 2. To evaluate their technical usefulness and to probe the local structure of the quasicrystals, pressure–composition isotherms ( p – c – T) were measured above 250 ° C using a computer-controlled apparatus. In the Ti–Zr–Ni quasicrystal, the p – c – T curves do not exhibit a clear pressure plateau. Instead, the equilibrium vapor pressure remains low ( < 5 Torr) below H / M ≈ 1 and increases sharply for increasing H/M. In the Ti–Zr–Ni 1/1 approximant phase, which is a large unit cell bcc structure ( a = 13.13 Å), the p – c – T measurements show similar curves with a hint of pressure plateau consistent with a structural similarity between the phases. The quasicrystals desorb most of the absorbed hydrogen above 600 ° C for 2 h in dynamical vacuum without phase transformation, and they do not become powder, even after a few absorption–desorption cycles. Interestingly, a small amount of Pd inhibits the growth of the (Ti,Zr)H x hydride phase during hydrogenation.