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

Abstract

Record greenhouse gas emissions have spurred the search for clean energy sources such as hydrogen (H₂) fuel cells. Metal–organic frameworks (MOFs) are promising H₂ adsorption and storage media, but knowledge of H₂ dynamics and adsorption strengths in these materials is lacking. Variable-temperature (VT) ²H solid-state NMR (SSNMR) experiments targeting ²H₂ gas (i.e., D₂) shed light on D₂ adsorption and dynamics within six representative MOFs: UiO-66, M-MOF-74 (M = Zn, Mg, Ni), and α-M₃(COOH)₆ (M = Mg, Zn). D₂ binding is relatively strong in Mg-MOF-74, Ni-MOF-74, α-Mg₃(COOH)₆, and α-Zn₃(COOH)₆, giving rise to broad ²H SSNMR powder patterns. In contrast, D₂ adsorption is weaker in UiO-66 and Zn-MOF-74, as evidenced by the narrow ²H resonances that correspond to rapid reorientation of the D₂ molecules. Employing ²H SSNMR experiments in this fashion holds great promise for the correlation of MOF structural features and functional groups/metal centers to H₂ dynamics and host–guest interactions.