Hydrogen Desorption Behavior of Nickel-Chloride-Catalyzed Stoichiometric Li4BN3H10

Quaternary Li-B-N-H hydrides with the alpha -phase crystal structure form over a range of compositions between Li3BN2H8 and Li4BN3H10 and have up to 11.9 wt % hydrogen capacity. Previous work has focused on the nonequilibrium Li3BN2H8 composition created by high energy ball milling because this composition shows maximum hydrogen release and minimum NH3 cogeneration. Here we report the hydrogen and NH3 release characteristics of alpha-phase material having the equilibrium Li4BN3H10 composition. In the absence of a dehydrogenation catalyst, this composition simultaneously releases H-2 and NH3 in roughly equal quantities by weight (or about 10% NH3 by volume) at temperatures above 240 degrees C. When Ni in the form of NiCl2 is added as a dehydrogenation catalyst, the H-2 release temperature is reduced by 122 degrees C. NH3 release, in contrast, still occurs only at the higher temperature. As a result, decomposition occurs in two steps separated in temperature, dominated by H-2 gas at low temperature and NH3 release at high temperature. This result clearly demonstrates that the two gases are evolved in two distinct decomposition reactions that are coincident in uncatalyzed Li4BN3H10, but can be separated by a dehydrogenation catalyst. We expect that NH3 cogeneration could be completely eliminated at sufficiently low dehydrogenation temperatures.