Reactivity with water vapor and hydrogen storage capacity of Be2Ti compound

Abstract

Beryllium intermetallic compounds show a variety of excellent properties such as neutron multiplication, refractory function, hydrogen storage, and superconductivity. Be12M compounds (M = Ti, V, and Zr) have been investigated as neutron multipliers for fusion reactors, while Be17M2 compounds have been explored as refractory materials. Furthermore, Be2Ms are known to have Laves phases, which are characterized by an A2B type compound having high H2 gas storage potential. Because of its low density, the hydrogen properties of Be2Ms have attracted great interest from viewpoints of reactivity with H2O, trap site of hydrogen, and amount of H2 gas in this compound. However, few studies have dealt with Be2M, and its database remains unsatisfactory.Preliminary synthesis of a beryllium intermetallic compound (=Be2Ti) as a hydrogen storage material was conducted to clarify its reactivity with water vapor at high temperatures and high hydrogen storage capacity. X-ray diffraction profiles and electron-probe microanalysis results confirmed that the preliminary synthesis of single-phase Be2Ti by homogenization treatment and plasma sintering was successful. The hydrogen generation rate of Be2Ti by reaction with 1% H2O increased as the test temperature increased. High temperature exposure to H2O led to the formation of TiO2 on the surface. Furthermore, the hydrogen gas storage concentration of Be2Ti, evaluated using the pressure–concentration–temperature curve, was 0.56 wt.% (=0.125 H/M) at 298 K, which is relatively low considering that H2 pressure was increased up to 13 MPa. Based on additional pressure–composition–temperature measurements, it does not appear to have particle size dependence with regard to hydrogen capacity.A simulation based on first-principles calculation indicated the presence of two hydrogen trap sites, tetrahedral and center of triangle with solution energies of −0.52 and −0.05 eV, respectively, implying that the maximum trap site of hydrogen with 5.4 wt.%. This dissimilarity might be attributed to the fact that the Be2Ti sample contained a large fraction of surface oxide layer, which disturbed the surface penetration of hydrogen.