Local bonding and atomic environments in Ni-catalyzed complex hydrides.
Abstract
The local bonding and at. environments in the Ni-catalyzed destabilized system LiBH4/MgH2 and the quaternary borohydride-amide phase Li3BN2H8, were studied by x-ray absorption spectroscopy. In both cases the Ni catalyst was introduced as NiCl2 and a qual. comparison of the Ni K-edge near-edge structure suggests the Ni2+ is reduced to primarily Ni0 after ball milling. The extended fine structure of the Ni K edge indicates that the Ni is coordinated by ∼3 boron atoms with an interat. distance of approx. 2.1 A and ∼11 Ni atoms in a split shell at around 2.5 and 2.8 A. 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 Ni3B. In the fully hydrogenated phase of LiBH4/MgH2 a small amt. Mg2NiHx was also present. Surface calcns. performed using d. functional theory suggest that the lowest kinetic barrier for H2 chemisorption occurs on the Ni3B(100) surface. [on SciFinder(R)]