MgBu₂ nanosheets encapsulated in ZIF-8 for producing carbon scaffold in situ nanoconfined Mg hydrogen storage materials: Record-high loading and decreased dehydrogenation enthalpy

Nanoconfinement is an effective strategy to improve the kinetic and thermodynamic properties of the Mg/MgH₂ system. However, current nanoconfinement approaches including porous scaffolds impregnation and surface anchoring can hardly obtain high loading, agglomeration resistant, and air-stable Mg nanoparticles. Herein, we report a novel strategy for preparing carbon scaffold in situ nanoconfined Mg hydrogen storage materials. The 12.2 nm MgBu₂ nanosheets precipitated by solvent displacement are encapsulated in ZIF-8 to prepare MgBu₂@ZIF-8, which are then pyrolyzed at 800°C to obtain Mg@C nanocomposites with 8.7 nm Mg embedded in a carbon scaffold. First principles calculations have demonstrated that the addition of MgBu₂ promotes the nucleation and growth of ZIF-8 to form MgBu₂@ZIF-8. It is worth noting that the loading rate of Mg@C-3 sample reaches a record high of 76.3% and exhibits outstanding hydrogen storage performances. Surprisingly, the enthalpy of hydrogen absorption/desorption sharply decreases to −62.0/63.1 kJ mol⁻¹ H₂. Mg@C-3 can absorb 4.4 wt% H₂ at 200°C and desorb 4.0 wt% H₂ at 250°C, and the activation energy for hydrogen absorption/desorption is reduced to a staggering 53.1/74.2 kJ mol⁻¹ H₂. Moreover, Mg@C-3 shows high cycling stability and antioxidant performance. This work opens a novel approach for the development of nanoconfined Mg nanocomposites with excellent performances.