Development of new composite material for hydrogen storage using mg as a binder

In most applications of metal hydrides, breaking into a very fine powder upon hydriding is one of the important problems to be solved. In this paper, we have developed new composite materials for hydrogen storage which contain LaNi₅, Zr(Fe_0.7Cr_0.3)₂ or TiMn_1.5 as the storage material and magnesium as a binder. The influence of composition, compacting pressure and heat treatment on the storage capacity and the stability behaviour of the pellets was investigated by repeating absorption-desorption cycles. The pellets obtained by sintering the mixture of Zr(Fe_0.7Cr_0.3)₂ and Mg powder at 773 K for 20 h absorb hydrogen easily and very fast under hydrogen pressures less than 1 MPa without any special activation treatment, and exhibits no significant decrease in hydrogen storage capacity without any disintegration after 1000 hydrogen absorption-desorption cycles. In order to clarify the origin of the improvement, we observed the microstructure and the distribution of the metals and oxygen atoms in the composite by SEM, EPMA and ESCA. The results indicate that the heat treatment at 773 K for 20 h not only promotes the so-called Mg reduction and makes the surface of the hydrides clean, but also it helps form a new thin composite phase on the boundary between the hydride and Mg metal, which acts as a binder, remaining the pellet intact upon hydriding.