A theoretical study of hybrid hydrogen adsorption: Mg nanoparticle-inserted Mg-MOF-74

Abstract

Metal-organic frameworks (MOFs) provide highly selective catalytic activity due to their porous crystalline structure. There is particular interest in metal nanoparticle-MOF composites (M NP@MOF) that could take advantage of synergistic effects for enhanced catalytic properties. We present an investigation into the local structure and electronic properties of Mg NP@Mg-MOF-74, which is composed of Mg nanoparticles and Mg-MOF-74. A theoretical study on the adsorption of multiple Mg2–Mg10 clusters at one pore in a 1 × 1 × 2 Mg-MOF-74 supercell is conducted, clearly showing that the small clusters tend to aggregate together when stabilized by bonds between Mg and O in the MOF. Considering the size and shape of the pore in the MOF, HCP-Mg nanoparticles with 60 Mg atoms are embedded in one pore of 1 × 1 × 2 Mg-MOF-74 to form nanowires. Results show that the mixture Mg NP@Mg-MOF-74 exhibits a better hydrogen adsorption performance than the isolated Mg nanoparticle, with a considerable estimated theoretical hydrogen storage capacity of 3.98 wt. %. The corresponding electronic structure analysis reveals that the accumulation of charges on H in the hybrid system is clearly enhanced with respect to the isolated Mg nanoparticles.