  AB5 compounds (A = rare earth, B = transition metal) have been widely studied
as anodes for Ni-MH applications. However, they have reached their technical
limitations and the search for new promising materials with high capacity is
foreseen. ABy compounds (2 < y < 5) are good candidates. They are made by
stacking [AB5] and [A2B4] units along the c crystallographic axis. The latter
unit allows a large increase in capacity, while the [AB5] unit provides good
cycling stability. Consequently, the AB3.8 composition (i.e. A5B19 with three
[AB5] for one [A2B4]) is expected to exhibit better cycling stability than the
AB3.5 (i.e. A2B7 with two [AB5] for one [A2B4]). Furthermore, substitution of
rare earth by light magnesium improves both the capacity and cycling stability.
In this paper, we compare the hydrogenation and corrosion properties of two
binary compounds SmNi$_{3.5}$ and SmNi$_{3.8}$ and two pseudo-binary ones
(Sm,Mg)Ni$_{3.5}$ and (Sm,Mg)Ni$_{3.8}$. A better solid-gas cycling stability
is highlighted for the binary SmNi$_{3.8}$. The pseudo-binary compounds also
exhibit higher cycling stability than the binary ones. Furthermore, their
resistance to corrosion was investigated.
