Effect of LiBH4 on hydrogen storage properties of magnesium hydride-carbon composite

In this paper, a magnesium hydride-carbon composite (MgH2@CS) was successfully synthesized by hydrogenation, employing magnesium powder and carbonized-starch (CS) as the raw material. The as-prepared MgH2@CS was ball-milled with LiBH4 to constitute a novel Li-Mg-B-H system (2LiBH4-MgH2@CS). Compared with the primary 2LiBH4-MgH2, the 2LiBH4-MgH2@CS composite showed a significant improvement in hydrogen storage performance. Temperature programmed desorption (TPD) analyses show that the 2LiBH4-MgH2@CS composite starts to slowly release hydrogen at about 150 °C, which is 245 °C lower than that of the pure 2LiBH4-MgH2; the final hydrogen desorption capacity reaches 9.3 wt% (LiBH4 with a weight loss of 7.0 wt%). In particular, the capacity retention rate of 2LiBH4-MgH2@CS reaches 80.5% after five reversible de/hydrogenation cycles at 400 °C. Microstructure analyses reveal that the CS with lamellar structure could not only serve as a support for anchoring well-dispersed MgH2 nanoparticles, but could also effectively prevent the aggregation and growth of Mg and magnesium hydrides during de/hydrogenation. Furthermore, the homogeneous nanosized Mg that is generated from decomposition of MgH2@CS has high reactivity, which could accelerate the decomposition of LiBH4 and meanwhile shorten the incubation period of MgB2, thereby greatly enhancing the kinetics of dehydrogenation. These studies provide us with fundamental insights into the design of the Li-Mg-B-H system.