H2 storage in isostructural UiO-67 and UiO-66 MOFs

Area of Science:

• Materials Science
• Chemistry

Background:

• The UiO-66/67/68 class of isostructural metal-organic frameworks (MOFs) are known for their remarkable stability.
• UiO-66, synthesized with a 1,4-benzene-dicarboxylate linker, is a well-established cubic MOF.

Purpose of the Study:

• To perform a complete structural, vibrational, and electronic characterization of the UiO-67 material.
• To evaluate and compare the molecular hydrogen storage capabilities of UiO-66 and UiO-67.

Main Methods:

• Laboratory X-ray powder diffraction (XRPD)
• Zr K-edge Extended X-ray Absorption Fine Structure (EXAFS)
• Thermogravimetric analysis (TGA)
• Fourier-transform infrared spectroscopy (FTIR)
• UV-Visible spectroscopy (UV-Vis)
• Periodic density functional theory (DFT) calculations

Main Results:

• UiO-67, synthesized with a longer 4,4'-biphenyl-dicarboxylate linker, exhibits increased Langmuir surface area (2483 m(2) g(-1)) and micropore volume (0.85 cm(3) g(-1)) compared to UiO-66.
• UiO-67 demonstrated a higher H(2) uptake of 4.6 mass% at 38 bar and 77 K, compared to 2.4 mass% for UiO-66.
• The study provides a comprehensive understanding of the structural, vibrational, and electronic properties of UiO-67 through experimental and computational methods.

Conclusions:

• The longer linker in UiO-67 enhances its suitability for molecular hydrogen storage by increasing surface area and pore volume.
• UiO-67 exhibits competitive hydrogen storage capacity, among the highest reported for MOFs, while maintaining remarkable chemical and thermal stability.
• The absence of chromium in UiO-67 makes it a potentially safer and more attractive material for hydrogen storage applications.