In Situ Neutron Powder Diffraction and X-ray Photoelectron Spectroscopy Analyses on the Hydrogenation of MOF-5 by Pt-Doped Multiwalled Carbon Nanotubes

초록

Recent research on hydrogen storage in metal-organic frameworks focuses on how to achieve increased hydrogen binding energies by using doped metal, using unsaturated metal ions, or forming composites comprising Pt-doped carbon materials. In particular, noticeable progress using MOFs and Pt-doped carbons has been achieved to enhance the hydrogen storage capacity near room temperature. A three-component composite material, Pt-MWCNT-MOFs (PMM5), which is a metal-organic framework (MOF-5) hybridized with Pt nanoparticles on multiwalled carbon nanotubes (MWCNT), stores 0.22 wt % hydrogen at 320 K and 30 bar, which is larger than 0.13 wt % at 300 K and 30 bar. Although the increased quantity is small, it is possible to detect the origin of uptake increase based on various analyses. In situ neutron diffraction experiments of deuterium-sorbed PMM5 with a temperature cycling process (D-2 loading at 50 K -> 4 K -> 320 K, 2 h -> 50 K -> 4 K) result in a significant background increase owing to both chemisorbed deuterium atoms and a local deformation of the MOF-5 framework. Hydrogen loading in PMM5 induces significant binding energy shifts in C Is and Zn 2p(3/2) electrons in the X-ray photoelectron spectra, suggesting the chemical environment change in Zn4O(COO)(6) coordination sphere in MOF-5. All accumulated experimental data support the fact that the hydrogen receptor is the oxygen atoms of benzene-1,4-dicarboxylates of MOF-5, which is facilitated by the embedded Pt-MWCNT.

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