Nanoconfined 2LiBH4–MgH2 for reversible hydrogen storages: Reaction mechanisms, kinetics and thermodynamics

Samples of nanoconfined Reactive Hydride Composites in resorcinol–formaldehyde aerogel scaffolds (RF–CAS) are prepared by (i) direct melt infiltration of bulk 2LiBH4–MgH2; and (ii) MgH2 impregnation and LiBH4 melt infiltration. The reaction mechanisms, kinetics and thermodynamics of the systems are concluded. Activation energy (EA) and dehydrogenation enthalpies of LiBH4 and MgH2 ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) of nanoconfined 2LiBH4–MgH2 are in this work of interest. The hydrogen sorption reactions in both nanoconfined samples are reversible as shown by the recovering of LiBH4 and MgH2 after rehydrogenation. The titration results show the remarkable improvement in desorption kinetics of nanoconfined samples over the bulk material, such as more than 90% of overall hydrogen storage capacity is obtained within 2 h from the nanoconfined samples during the 1st dehydrogenation, while that of bulk material needs more than 16 h. The activation energy of the composites decreases by 27–170 kJ/mol (ΔEA) due to nanoconfinement. For thermodynamics, ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) calculated from DSC results of the nanoconfined samples are in the range of 41–46 kJ/mol H2.