Low temperature thermolysis and hydrolysis of MgH2 generated from a titanium-mediated hydrogenation of Mg2Si

The magnesium-silicon hydrogen storage system (Mg 2 Si+H 2 ↔MgH 2 +Si) has attracted considerable attention with the potential of achieving near-room temperature hydrogen sorption since the reaction enthalpy is only ∼36.8 kJ/mol H 2 , offering much better thermodynamic properties over MgH 2 . However, the rehydrogenation of Mg 2 Si faces significant kinetic barriers, restricting its practical utilization. In this work, hydrogen-assisted high-energy ball milling (HHBM) was employed to hydrogenate Mg 2 Si. XRD and HRTEM results confirmed that Mg 2 Si was successfully converted into MgH 2 under the influence of titanium (Ti), achieving a conversion rate up to 76%. Aberration-corrected TEM (AC-TEM) revealed that in situ formed MgH 2 and titanium silicide (TiSi 2 ) were homogenously mixed with robust interfaces. Such a growth mode reduces the migration path of Si atoms and the stability of Mg 2 Si, thus promoting the formation of MgH 2 . Furthermore, the as-synthesized MgH 2 particles with ultrafine particle size and adjacent catalysts show superior thermolysis and hydrolysis performances. Consequently, the composite exhibits excellent hydrogen storage properties, absorbing 50% of its total hydrogen capacity at room temperature and initiating dehydrogenation at 114.3 °C. In situ synchrotron X-ray diffraction (ISXRD) confirms the dehydrogenation of in situ generated ultrafine MgH 2 and part of TiSi 2 is converted to Mg 2 Si at 283 °C. In addition, the ultrafine, defect-rich MgH 2 particles show favorable hydrolysis kinetics and high conversion efficiency at relatively low temperatures (91.9% of the hydrogen yield can be achieved at 5 °C). This method developed in this work exhibits a new way to synthesize high-performance hydrogen storage materials.