M. Pasturel

Various ways including substitution and protection used to improve the cyclability of ‘MgNi’ electrodes

Three different treatments have been investigated to improve the cyclability in KOH electrolyte of ‘MgNi’ used as hydrogen storage electrode material for Ni–MH batteries. Whereas hydrophobic molecule grafting does not give significant improvement, replacement of Mg by Ti or coating the ‘MgNi’ powder with copper in a supercritical CO2–EtOH mixture increase strongly the resistance of the electrode against hydroxylation: the capacity after 12 cycles is 98% higher for ‘Mg0.5Ti0.5Ni’ and 45% higher after coating by a thin copper film in comparison with the raw ‘MgNi’ material.

Structure and magnetic properties of the ternary gallides CeMGa (M=Mn, Co and Cu) and their hydrides

The ternary gallides CeMGa present various structural properties since CeMnGa, CeCoGa and CeCuGa crystallize, respectively, in the cubic MgCu2-, monoclinic CeCoAl-, and orthorhombic CeCu2-type structure. These compounds absorb hydrogen at room temperature but hydrogenation induces a change of the crystalline structure: (i) CeCoGaH3.0 and CeCuGaH0.8 adopt the hexagonal AlB2-type; (ii) on the contrary, the cubic MgCu2 structure is preserved for CeMnGaH1.6. Moreover, in some cases hydrogenation leads to a valence change for Ce. For instance, CeCoGa is considered as intermediate valence compound, whereas CeCoGaH3.0 contains Ce3+. This paper demonstrates that hydrogenation strongly influences the Kondo effect in these intermetallics.