Local bonding and atomic environments in Ni-catalyzed complex hydrides.
The local bonding and atomic 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 qualitative 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 approximately 3 boron atoms with an interatomic distance of approximately 2.1 A and approximately 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 amount Mg2NiHx was also present. Surface calculations performed using density functional theory suggest that the lowest kinetic barrier for H2 chemisorption occurs on the Ni3B(100) surface.
Department of Energy Sciences and Technology, Brookhaven National Laboratory, Upton, NY 11973, USA.
J
J
Graetz
S
S
Chaudhuri
T T
TT
Salguero
J J
JJ
Vajo
M S
MS
Meyer
F E
FE
Pinkerton
D001881:Borates / Q000737:chemistry*; D002384:Catalysis; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D006859:Hydrogen / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008956:Models, Chemical; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D009532:Nickel / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties
D001881:Borates; D018020:Lithium Compounds; D046911:Macromolecular Substances; D009532:Nickel; D006859:Hydrogen; C021051:lithium borate