Relevance of hydrogen storage properties of ANi3 intermetallics (A = La, Ce, Y) to the ANi2 subunits in their crystal structures

To understand the fundamental reason for the poor stability in hydrogen storage, the cycling behavior of ANi3 intermetallics (A = La, Ce, Y) under hydrogen was systematically investigated and compared with the stability of the corresponding ANi2 intermetallics. All cycled ANi3 intermetallics are subject to amorphization to some extent, similar to corresponding ANi2 intermetallics. Since the crystal structure of ANi3 intermetallics consists of an alternating stacking between the ANi5 subunit and the ANi2 subunit, the hydrogen-induced amorphization as observed in ANi3 intermetallics is assumed to associate with the ANi2 subunits in their crystal structures. This assumption is supported by the experimental results obtained in the present work.