New insights into the thermal desorption of the 2LiNH2 + KBH4 + LiH mixture

In situ two-dimensional synchrotron X-ray powder diffraction investigation combined with Rietveld method data analysis were performed in order to yield a complete and quantitative phases structure evolution of the polycrystalline mixture 2LiNH2 + KBH4 + LiH during H2 desorption. While a first-principles, purely thermodynamics approach of the system predicted a single dehydrogenation step reaction at relatively low temperatures, it is assessed experimentally that the reaction occurs in two steps with first the formation of Li2NH at ca. 230 C due to the reaction between LiNH2 and LiH plus hydrogen and ammonia evolution, followed by an additional reaction of the resulting phases with KBH4 at 360 C,which releases hydrogen and leads to the formation of the monoclinic and tetragonal Li3BN2 polymorphs. Besides pointing out possible limits of a purely thermodynamics approach inevitably relying exact knowledge of experimental quantities, it is concluded that before assuming it viable for on-board vehicle use, additional stoichiometries may be worth of investigation in order to assess any existence of lower hydrogen desorption temperature of such system.

VALENTONI Antonio;  GARRONI Sebastiano;  PISTIDDA Claudio;  MASOLO Elisabetta;  NAPOLITANO Emilio;  MORETTO Pietro;  DORNHEIM Martin;  MULAS Gabriele;  ENZO Stefano; 

2015-12-10

PERGAMON-ELSEVIER SCIENCE LTD

JRC98280

0360-3199,   

http://www.sciencedirect.com/science/article/pii/S0360319914022150,    https://publications.jrc.ec.europa.eu/repository/handle/JRC98280,   

10.1016/j.ijhydene.2014.07.169,