Nanoscale structural characterization of Mg(NH3)6Cl2 during NH3 desorption: An in situ small angle X-ray scattering study

Complex metal hydrides progressively display improved hydrogen storage capacity, but they are still far from fulfilling the requirements of the transport sector. Recently, indirect storage of hydrogen as ammonia in Mg(NH3)6Cl2 has shown impressive capacity and reversibility. Here, we present an in situ nanoscale structural characterization of the thermal decomposition of Mg(NH3)6Cl2 using small angle X-ray scattering (SAXS). We observe the growth of polydisperse spherical Mg(NH3)2Cl2 crystallites forming a skeletal structure, the subsequent agglomeration of MgCl2 and formation of a nanoscale porosity consisting of 25–30 nm wide channels, which may account for the exceptional fast reloading of the material.