4384
J. Phys. Chem. C 2008, 112, 4384-4390
Hydrogen Storage Properties in (LiNH2)2-LiBH4-(MgH2)X Mixtures (X ) 0.0-1.0) Andrea Sudik,*,† Jun Yang,† Devin Halliday,† and Christopher Wolverton‡ Ford Motor Company, Research and AdVanced Engineering, MD 1170/RIC, P.O. Box 2053, Dearborn, Michigan 48121, and Department of Materials Science and Engineering, Northwestern UniVersity, 2220 Campus DriVe, EVanston, Illinois 60208 ReceiVed: October 11, 2007
We have recently reported the synthesis and properties of a novel hydrogen storage composition comprised of a 2:1:1 molar ratio of three hydride compounds: lithium amide (LiNH2), lithium borohydride (LiBH4), and magnesium hydride (MgH2). This new ternary mixture possesses improved hydrogen (de)sorption attributes (relative to the individual compounds and their binary mixtures), including facile low-temperature kinetics, ammonia attenuation, and partial reversibility. Comprehensive characterization studies of its reaction pathway revealed that these favorable hydrogen storage properties are accomplished through a complex multistep hydrogen release process. Here, we expound on our previous findings and determine the impact of MgH2 content on the resulting hydrogen storage properties by examining a series of (LiNH2)2-LiBH4-(MgH2)X reactant mixtures (i.e., 2:1:X molar ratio) where X ) 0, 0.15, 0.25, 0.40, 0.50, 0.75, and 1.0. Specifically, we characterize each starting composition (after ball-milling) using powder X-ray diffraction (PXRD) and infrared spectroscopy (IR) and find that addition of MgH2 facilitates a spontaneous milling-induced reaction, introducing new species (Mg(NH2)2 and LiH) into the hydride composition. We additionally measure the relative hydrogen and ammonia release amounts for each mixture using temperature-programmed desorption mass spectrometry (TPD-MS) and find that ammonia liberation is suppressed for increasing values of X (
