Local bonding and atomic environments in Ni-catalyzed complex hydrides

The local bonding and atomic environments in the Ni-catalyzed destabilized system LiBH(4)/MgH(2) and the quaternary borohydride-amide phase Li(3)BN(2)H(8), were studied by x-ray absorption spectroscopy. In both cases the Ni catalyst was introduced as NiCl(2) and a qualitative comparison of the Ni K-edge near-edge structure suggests the Ni(2+) is reduced to primarily Ni(0) after ball milling. The extended fine structure of the Ni K edge indicates that the Ni is coordinated by similar to 3 boron atoms with an interatomic distance of approximately 2.1 angstrom and similar to 11 Ni atoms in a split shell at around 2.5 and 2.8 angstrom. These results, and the lack of long-range order, suggest that the Ni is present as a disordered nanocluster with a local structure similar to that of Ni(3)B. In the fully hydrogenated phase of LiBH(4)/MgH(2) a small amount Mg(2)NiH(x) was also present. Surface calculations performed using density functional theory suggest that the lowest kinetic barrier for H(2) chemisorption occurs on the Ni(3)B(100) surface.