In this study the hydrogen storage characteristics of several new destabilized borohydride systems were compared to the hydrogen storage behavior of MgH_2. The mixtures included: Mg(BH_4)_2/Ca(BH_4)_2; Mg(BH_4)_2/CaH_2/3NaH; and Mg(BH_4)_2/CaH_2; systems. Temperature programmed desorption, TPD, analyses showed that the desorption temperature of Mg(BH_4)_2 can be lowered by ball milling it with these additives. The PCT isotherm of the resulting mixtures displayed well-defined plateau regions. The desorption kinetics of Mg(BH_4)_2, Ca(BH_4)_2 and their 5:1 mixture were also compared in the two-phase region at the same temperature and thermodynamic driving force. The rate of hydrogen desorption from the Mg(BH_4)_2/Ca(BH_4)_2 mixture was faster than that from either of the constituents. Modeling studies showed hydrogen release from Mg(BH_4)_2, during the first 80% of the reaction, is diffusion controlled while in Ca(BH_4)_2 it is phase boundary controlled. In the mixture the rate appears to be under the mixed control of both processes. Lithium amide / magnesium hydride mixtures with an initial molar composition of 2LiNH_2 + MgH_2 were also studied with and without the presence of 3.3 mol% potassium hydride dopant. TPD analyses showed that the KH doped samples had lower onset temperatures than their corresponding pristine samples. The de-hydriding kinetics of the doped and pristine mixtures was compared at a constant pressure driving force. The addition of KH dopant was found to significantly increase hydrogen desorption rate from the (2LiNH_2 + MgH_2) mixture.
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