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The hydrogenation at different temperatures and hydrogen pressures of the binary intermetallic compound CeNi was studied. A hydride with the composition CeNiH 2.9(1) was obtained by hydriding the host alloy at 293 K and P H2 Z1 MPa. With increasing temperature of hydriding a reaction of hydrogenolysis of CeNi occurred with formation of a stable two-phase product composed of CeH 2.51 and CeNi 5 . The newly prepared hydride CeNiH 2.9(1) was found to be isostructural with CeNi (orthorhombic, CrB-type, S.G. Cmcm). On the basis of refinement of the XRD patterns of both the intermetallic compound and its hydride, the atomic positions of Ce and Ni and the interatomic distances were determined. The probable sites of hydrogen intersection in the host structure were proposed. Moreover, a valence transition of cerium from intermediate valence (CeNi) to the trivalent state (CeNiH 2.9 ) was evidenced by magnetization measurements. q

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The hydrogen sorption properties of the composites 85 wt.% Mg-15 wt.% Mg Ni Fe (x50, 0.1 and 0.3) prepared by high-energy 2 12x x ball milling were studied. It was shown that the presence of a Mg Ni Fe additive significantly improved the kinetics of hydrogen 2 12x x absorption and desorption of magnesium, the absorption capacity remaining sufficiently high even at temperatures between 423 and 573 K. The catalytic effect of the Mg Ni Fe intermetallics was explained as due to the formation of a second hydride, Mg NiH , to the 2 12x x 2 4appearance during the mechanical alloying of defects facilitating the formation of hydride nuclei and to the presence of Ni and Fe clusters on the surface of nanocomposite particles.

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