Mechanochemical Ligand Substitution in HKUST-1: Defect-Driven Enhancement of Hydrogen Storage Performance (#2024)

Authors

Gauna, Pablo

Barrera Díaz, Deicy

Abstract

Hydrogen storage remains a major challenge due to its inherently low energy density (0.01 MJ/L compared to 34 MJ/L for gasoline), requiring compression for practical applications. Conventional storage methods (e.g., compression, liquefaction) present significant drawbacks, including safety concerns and high energy costs. An alternative approach is storage in sorbent materials, where Metal-Organic Frameworks play a crucial role due to their tunable properties and chemical and thermal stability. Among these materials, HKUST-1, composed of copper dimers coordinated with 1,3,5-benzenetricarboxylic acid, has emerged as a promising candidate, prompting extensive research into strategies for enhancing its storage performance. This study investigates the effect of structural modifications in HKUST-1 on its adsorption behavior through a mixed-ligand approach. Three novel materials were synthesized with varying ligand ratios and characterized using nuclear magnetic resonance to determine their composition, powder X-ray diffraction and scanning electron microscopy for structural analysis, and thermogravimetric analysis to assess thermal stability. Additionally, textural properties were evaluated from nitrogen adsorption-desorption isotherms at 77 K, while hydrogen uptake experiments were conducted at 77 K up to 8 bar. One of the modified materials exhibited a remarkable 78% increase in H₂ uptake compared to HKUST-1, which is attributed to changes in the coordination environment of copper. Furthermore, although the original framework was preserved, a slight reduction in structural stability was observed. These findings highlight the potential of ligand substitution as an effective strategy for enhancing MOF-based hydrogen storage materials.