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.