Hydrogen storage properties in (LiNH2)2-LiBH4-(MgH2)X mixtures (X=0.0-1.0)

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 (< 0.1 wt % NH3 for X = 1). Kinetic hydrogen desorption data reveal a low-temperature reaction step (centered at similar to 160 degrees C) for all MgH2-containing samples which grows in intensity for larger values of X (up to similar to 4.0 wt % H-2 for X =1). Finally, we characterize desorbed samples to investigate the dependence of X (MgH2 amount) on the resulting distribution of observed product phases. These data are used to understand how MgH2 contributes to and impacts the low- and high-temperature hydrogen release events through comparing theoretical (based on the previously proposed reaction set) and observed desorption data for these reactions.