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

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, Ti45Zr38Ni17 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)Hx hydride phase during hydrogenation.