Design of hydrogen storage alloys in view of chemical bond between atoms

The chemical interactions operating in hydrogen storage alloys are simulated by the DV-Xα molecular orbital method, using tetrahedral or octahedral model clusters. It is found that hydrogen interacts more strongly with hydride non-forming elements, B (e.g., Ni, Fe) than hydride forming elements, A (e.g., La, Ti, Mg), in agreement with our previous calculations of hydrogen storage alloys (e.g., LaNi5, TiFe, Mg2Ni). However, it is noted that such a B–H interaction is not dominant unless A elements exist in the neighborhood, so that both A and B are indeed essential elements for hydrogen storage alloys. Also, it is shown that the A/B compositional ratio of hydrogen storage alloys can be understood in terms of a simple parameter, 2 Bo(A–B)/[Bo(A–A)+Bo(B–B)], where the Bo(A–B), Bo(A–A) and the Bo(B–B) are the bond strengths between atoms given in the parentheses.