  Intermetallic compounds are key materials for energy transition as they form
reversible hydrides that can be used for solid state hydrogen storage or as
anodes in batteries. ABy compounds (A = Rare Earth (RE); B = transition metal;
2 < y < 5) are good candidates to fulfill the required properties for practical
applications. They can be described as stacking of AB5 and AB2 sub-units along
the c crystallographic axis. The latter sub-unit brings a larger capacity,
while the former one provides a better cycling stability. However, ABy binaries
do not show good enough properties for applications. Upon hydrogenation, they
exhibit multiplateau behavior and poor reversibility, attributed to H induced
amorphization. These drawbacks can be overcome by chemical substitutions on the
A and/or the B sites leading to stabilized reversible hydrides. The present
work focuses on the pseudo-binary Sm2MnxNi7-x system (0 <= x < 0.5). The
structural, thermodynamic and corrosion properties are analyzed and interpreted
by means of X-ray diffraction, chemical analysis, scanning electron microscopy,
thermogravimetric analysis and magnetic measurements. Unexpected cell parameter
variations are reported and interpreted regarding possible formation of
structural defects and uneven Mn distribution within the Ni sublattice.
Reversible capacity is improved for x > 0.3 leading to larger and flatter
isotherm curves, allowing for reversible capacity >1.4 wt %. Regarding
corrosion, the binary compound corrodes in alkaline medium to form rare earth
hydroxide and nanoporous nickel. As for the Mn-substituted compounds, a new
corrosion product is formed in addition to those above mentioned, as manganese
initiates a sacrificial anode mechanism taking place at the early corrosion
stage.
