Grasping hydrogen adsorption and dynamics in metal-organic frameworks using (2)H solid-state NMR

Area of Science:

• Materials Science
• Chemistry
• Energy Storage

Background:

• Growing greenhouse gas emissions necessitate clean energy solutions like hydrogen fuel cells.
• Metal-organic frameworks (MOFs) are being investigated as potential materials for hydrogen adsorption and storage.
• Understanding hydrogen dynamics and binding affinities within MOFs is crucial for optimizing their performance.

Purpose of the Study:

• To investigate hydrogen (H2) adsorption and dynamics in six representative MOFs using deuterium (D2) gas.
• To correlate MOF structural characteristics with H2 host-guest interactions.
• To evaluate the potential of variable-temperature (2)H solid-state NMR (SSNMR) for probing H2 behavior in MOFs.

Main Methods:

• Variable-temperature (2)H solid-state NMR (SSNMR) experiments were conducted on D2 gas adsorbed in six MOFs.
• The MOFs studied include UiO-66, M-MOF-74 (M = Zn, Mg, Ni), and α-M3(COOH)6 (M = Mg, Zn).
• Analysis of (2)H SSNMR powder patterns and resonance widths provided insights into D2 dynamics and binding strengths.

Main Results:

• Strong D2 binding was observed in Mg-MOF-74, Ni-MOF-74, α-Mg3(COOH)6, and α-Zn3(COOH)6, indicated by broad (2)H SSNMR patterns.
• Weaker D2 adsorption was found in UiO-66 and Zn-MOF-74, characterized by narrow (2)H resonances and rapid D2 reorientation.
• The results demonstrate distinct differences in H2 adsorption behavior across the studied MOF structures.

Conclusions:

• Variable-temperature (2)H SSNMR is an effective technique for characterizing H2 dynamics and adsorption in MOFs.
• MOF structural features, functional groups, and metal centers significantly influence H2 binding strength and mobility.
• This approach holds promise for designing advanced MOFs tailored for efficient hydrogen storage applications.