Investigating structural and dyanmical information of H2 inside materials
Yun Liu*, Craig Brown, Michael R. Hartman, Vanessa K. Peterson, Dan A. Neumann, Terry Udovic, David Narehood , Peter Eklund, Steven S. Kaye, and Jeffrey R. Long
A clear understanding of the physio-chemical properties of hydrogen inside materials is crucial to rationally improve overall efficiency of H2 storage, especially in the automobile industry. Neutron scattering techniques have been proven to be extremely useful in observing H2 molecules on the nano-scale due to the very large neutron scattering cross section. We present investigations of H2 absorbed inside two different materials, dehydrated Prussian blue analogue, and boron doped carbon nanotubes.
The dehydrated Prussian Blue analogue, Cu3[Co(CN)6]2, is capable of absorbing H2 up to 1.7 wt% at 77 K and 1 atm. This is larger than the 1.3 wt% H2 absorption of MOF5 at 77 K and 1 atm although MOF5 is a very promising candidate for H2 storage and can absorb H2 up to ~10 wt% at very low temperature. Neutron powder diffraction and Rietveld analysis indicates H2 molecules are absorbed into two crystallographic sites. The rotational energy spectra of H2 measured by neutron vibrational spectroscopy indicate large variations of local potential, which is consistent with vacancies present in the material.
Boron substitution in carbon nanotubes is theoretically believed to enhance the H2 binding energy and improve the hydrogen storage capability compared to regular carbon nanotubes. By measuring the rotational energy spectra of H2, we find evidence that the substituted boron atoms in the carbon nanotube can absorb only one H2 molecule before it becomes favorable for H2 to be absorbed onto other carbon surfaces.