Improved hydrogen storage performances of LiAlH 4 + Mg( BH 4 ) 2 composite with TiF 3 addition

This paper studies on the preparation of the alanate-borohydride combined system, LiAlH4 + Mg(BH4)2 with diverse molar ratios (1:1, 1:2, and 2:1) using the ball milling technique. The findings show that there is a mutual destabilization between the hydrides where the newly combined system has superior hydrogen storage performances as opposed to the unary components (LiAlH4 and Mg[BH4]2). Analysis on the initial decomposition temperature and isothermal de/hydrogenation kinetics has proven that the 2LiAlH4 + Mg(BH4)2 system possesses better performance. In an endeavor to ameliorate the performances of the hydrogen storage of 2LiAlH4 + Mg(BH4)2, the destabilized system was doped with TiF3. Three major steps of desorption were detected during the heating process in the 2LiAlH4 + Mg(BH4)2 system with and without the addition of TiF3, which are correlated to the decomposition of Mg(AlH4)2, MgH2 and LiBH4. It is found that 2LiAlH4 + Mg(BH4)2 + 5 wt.% TiF3 has decreased the initial decomposition temperature at about 60°C, which is 55°C lower than the non-catalyzed 2LiAlH4 + Mg(BH4)2 system. The isothermal absorption/desorption kinetics of the 2LiAlH4 + Mg(BH4)2 system have also been enhanced by the addition of TiF3. The activation energy for Mg(AlH4)2-, MgH2-, and LiBH4-relevant decomposition after doped 2LiAlH4 + Mg(BH4)2 with TiF3 are reduced to 36.5, 23.3, and 17.6 kJ mol−1. Studies on the structural characteristics analysis of the 2LiAlH4 + Mg(BH4)2 + TiF3 sample hint to the fact that the formation of the MgF2, LiF, TiH2 and Ti-Al species, during desorption, is the main responsible factor for the observed thermodynamics change of the reactions by modifying the dehydrogenation and hydrogenation pathway. The catalytic role played by TiF3 may have encouraged the interaction between Mg(AlH4)2, MgH2, and LiBH4, further ameliorate the de/hydrogenation of the 2LiAlH4 + Mg(BH4)2 + TiF3 destabilized system.