Enhanced Dehydrogenation Properties of Modified Mg(NH2)2−LiBH4 Composites

Abstract

Promotion of dehydrogenation based on a combination of [BH] and [NH] sources has been demonstrated to be an effective approach in developing an advanced borohydride/amide multicompound hydrogen storage system. In this article, the hydrogen storage properties of Mg(NH2)2−LiBH4 composite are studied systematically. It has been shown that the Mg(NH2)2−LiBH4 binary system exhibits an onset dehydrogenation temperature of 250 °C, accompanied by an emission of 5.5 mol % ammonia. Further investigation has revealed that addition of metal chlorides results in significant improvement of the dehydrogenation of Mg(NH2)2−LiBH4. In particular, with NiCl2 addition up to 20 wt %, the modified composite exhibits more favorable thermodynamics, as demonstrated by an onset dehydrogenation temperature as low as 60 °C, accompanied by the suppressed evolution of byproduct NH3 (2 mol %), which enables this modified system to release 7.3 wt % hydrogen in the temperature range of 60−400 °C, which is vastly superior compared with the dehydrogenation of Mg(NH2)2−LiBH4 alone. X-ray diffraction results indicate that the presence of Mg(NH2)2 results in an accelerated exchange reaction between LiBH4 and NiCl2, which may be the dominant reason for the improved thermodynamics and kinetics in the NiCl2-added Mg(NH2)2−LiBH4 system.