Hydrogen sorption properties of MgH2–LiBH4 composites

A detailed analysis of the reaction mechanism of the reactive hydride composite (RHC) MgH2 + 2LiBH4 ↔ MgB2 + 2LiH + 4H2 was performed using high-pressure differential scanning calorimetry (HP-DSC) measurements and in situ synchrotron powder X-ray diffraction (XRD) measurements along with kinetic investigations using a Sievert-type apparatus. For the desorption the following two-step reaction has been observed: MgH2 + 2LiBH4 ↔ Mg + 2LiBH4 + H2 ↔ MgB2 + 2LiH + 4H2. However, this reaction is kinetically restricted and proceeds only at elevated temperatures. In contrast to the desorption reaction, LiBH4 and MgH2 are found to form simultaneously under fairly moderate conditions of 50 bar hydrogen pressure in the temperature range of 250–300°C. As found in pure light metal hydrides, significant improvement of sorption kinetics is possible if suitable additives are used.