High reversible capacity hydrogen storage through Nano-LiBH4 + Nano-MgH2 system

A nano-LiBH4 ​+ ​nano-MgH2 mixture which can reversibly release and absorb ∼5.0 wt% H2 at 265 °C is synthesized via a new processing method, termed as Ball Milling with Aerosol Spraying (BMAS) established in this study. The reversible storage capacity of ∼5.0 wt% H2 is the highest one ever reported for the LiBH4 + MgH2 system at temperature ≤265 °C. It is found that the unusually high reversible hydrogen storage is accomplished through two parallel reaction pathways. One is nano-LiBH4 decomposes to form Li2B12H12 and H2 first and then Li2B12H12 reacts with MgH2 to form MgB2, LiH and H2. The other is nano-MgH2 decomposes to form Mg and H2 first and then Mg reacts with LiBH4 to form MgB2, LiH and H2. These reaction pathways become possible because of the presence of nano-LiBH4 and nano-MgH2 and their intimate mixing, enabled by the BMAS process. This study unambiguously shows that nano-engineering can overcome kinetics barriers for thermodynamically favorable systems like the LiBH4 ​+ ​MgH2 mixture and even provides thermodynamic driving force to enhance hydrogen release at low temperature. The principle established in this study also opens up a new direction for investigating and improving the hydrogenation and dehydrogenation properties of many other systems containing multiple hydride components that have favorable thermodynamic properties for reversible hydrogen storage, but with limited kinetics.