X-ray diffraction and Raman spectroscopy were used to analyze samples of NaBH4 destabilized with MgH2 or TiH2 and nanostructured within a metal-organic framework. MgH2 successfully lowered the desorption temperature of NaBH4 to 500°C, while TiH2 showed no destabilization effect. Raman spectroscopy could not detect NaBH4 embedded within the MOF, requiring alternative analytical methods. Ultra-small angle X-ray scattering showed NaBH4 nanostructured samples had higher scattering intensity than MOF alone, indicating NaBH4 was within or surrounding the MOF. Future work will optimize ratios and testing methods to further lower desorption temperatures and confirm successful nanostructuring.

1. X-ray Diffraction (XRD)
Figure 1. MgH2 +NaBH4. Figure 2. TiH2 +NaBH4.
Raman Spectroscopy
Figure 3. Raman peaks/images for Kapton Tape, NaBH4 , MOF, and NaBH4+MoF(Bottom to Top).
Ultrasmall Angle X-ray Scattering (USAXS)
Figure 4. USAXS data for MgH2 destabilized NaBH4 (left) and NaBH4 in MOF (right).
Techniques
XRD
X-Ray Diffraction (XRD) is a useful technique that uses X-rays to
measure the bond distance inside molecules of powders or thin
films. It is effective in determining lattice structure of crystalline
materials and molecular composition, but loses accuracy with
organic materials or thick layered materials. For this reason analysis
of nanostructured materials is difficult and is why we attempted to
use Raman spectroscopy to analyze NaBH4 in a Metal Organic
Framework (MOF).
Raman
Raman spectroscopy measures bond vibrations between atoms
based on Raman Scattering from monochromatic light. Its uses
typically involve molecule identification and identifying changes in
molecular structures. In this case, Raman spectroscopy is being
used to identify NaBH4 imbedded inside a MOF after it is
nanostructured. The goal is to be able to identify NaBH4 inside the
MOF before desorption and identify its absence after desorption,
something that cannot be done by X-Ray Diffraction.
USAXS
Ultra Small Angle Scattering (USAXS) is a method that measures
quantitative and qualitative information about the microstructure of a
material, up to millimeter sized structures. Scattering intensity is
measured as a function of q, scattering vector, which can be used to
derive shape and size of microstructures. This is useful, in that it
makes comparing an empty MOF, which is very porous, to a MOF
imbedded with NaBH4 which would show up as solid. It tells how
large the pores are in the MOF, giving an idea of the molar ratio of
the MOF to material that can be used.
Schematic diagram of the USAXS instrument
Overview
The need for alternate energy sources is becoming critical for our
future. Electric engines have become powerful enough to satisfy
most motor vehicle needs but batteries are still decades away from
what they need to be. Hydrogen fuel cells are a great and efficient
method of running an electric engine but, in its natural state,
hydrogen is highly explosive and hard to transfer/contain. The drive
for an efficient and safe storage medium for hydrogen sparked the
interest for hydrides, which have the ability to store hydrogen in a
stable solid state. The goal of this project was to determine if NaBH4
would be a viable medium in which to store hydrogen.
Last semester was dedicated to lower the desorption temperature of
NaBH4 to make bring it within the range to be useful. Two methods
were used, destabilization and nanostructuring.
This semester was focused on analyzing NaBH4 and the other
materials used in previous experiments to better understand their
properties.
Raman Spectroscopy was tested as a method to determine if NaBH4
desorbed and if nanostructuring was successful or not.
Samples were tested at Argonne National Laboratories in order to
measure their large scale aspects with Ultra Small Angle X-ray
Scattering (USAXS).
Results and Future Work
XRD Data:
• MgH2 proved to be a reliable destabilization agent for
NaBH4 in a 1:1 molar ratio. It lowered the desorption
temperature of the complex hydride down to 500°C.
TiH2 showed no signs of a successful destabilization of
NaBH4.
• Destabilizing the hydride was successful with MgH2 but
not with TiH2.
• Future work with further tweaking of the ratios could
further lower desorption temperature by a considerable
amount. Though TiH2 showed no signs of a successful
destabilization of NaBH4, by altering the parameters of
the experiment could provide better results. . By
altering the ratio to favor NaBH4 should show higher
overall peaks of the complex hydride and the potential
products of its desorption. With this, it will later have to
be determined whether or not the time of heating will
have to be increased. Increasing of the temperature
will be of no use because if it cannot lower the
desorption temperature than it is not destabilizing
NaBH4.
Raman Data:
• Nanostructuring NaBH4 using a MOF was not
successful. The Raman of the MOF samples in with
the NaBH4 imbedded inside does not show the NaBH4
peak seen in the sample of just the NaBH4 (at 2333
cm-1 wave number).
• Future work will examine changing the ratios of MOF
to NaBH4 powder (and also the overall content of
powder in the THF). It is also necessary to find another
method to test for successful nanostructuring as well
as to analyze the samples. Raman spectroscopy may
not have the sensitivity needed to measure for small
amounts of NaBH4 within MOFs.
USAXS Data:
• All of the hydrides show a -3 slope at low scattering
angle (q-vector), indicating that the hydrides
themselves are highly porous (surface fractals).
• The MgH2 shows a slope of -4 at high scattering angle,
indicating that the hydride is comprised of small dense
particles.
• The NaBH4 is either within or surrounding the MOF, as
the MOF-only sample has scattering intensity of less
than 0.01 cm-1 sr1 while the MOF sample containing
the NaBH4 (as well as NaBH4 along) shows scattering
intensity above 0.1 cm-1 sr1 at the same scattering
angle (q-vector).
• Future work include microstructure models to the
USAXS data in order to quantify these microstructures
(i.e. surface area, pore size, pore volume, particle size,
etc.).
References
1. Alapati, Sudhakar V., Johnson, J. Karl, Sholl, David S., “First Principals Screening of Destabilized
Metal Hydrides for High Capacity H2 Storage using Scandium”, Journal of Alloys and Compounds,
446-447, 23-27(2007).
2. Daniel, Reed and David, Book. “Recent applications of Raman spectroscopy to the study of
complex hydrides for hydrogen storage.” School of Metallurgy and Materials, University of
Birmingham. 15 (2011) 62–72.
3. Levine, L. E. and Long, G. G. “X-ray imaging with ultra-small-angle X-ray scattering as a contrast
mechanism.” Journal of Applied Crystallography. 0021-8898(2004).
4. Mao, J.F., Yu X.B., Guo Z.P., Liu H.K., Ni J., “Enhanced Hydrogen Storage Performances of
NaBH4- - MgH2 System”, Journal of Alloys and Compounds, 479, 619-623(2009).
5. Yang, Jun, Sudik, Andrea, Wolverton, C., “Destabilizing LiBH4 with a Metal( M= Mg, Al, Ti, V, Cr, or
Sc) or Metal Hydride (MH2 = MgH2, TiH2, or CaH2”, J. Phys. Chem., 111, 19134-19140(2007).
Acknowledgements
We wish to thank Mr. Christopher Bennett for help in learning how to operate the glovebox and
perform the ball milling of hydrides. We also thank Dr. Jan Ilavsky at the Advanced Photon Source for
help in measuring our USAXS data.
Analysis of NaBH4 for Hydrogen Storage
Nicholas S. Riffitts, Joseph Iannello, and Tabbetha Dobbins
Dept. of Physics & Astronomy, College of Science & Mathematics, Rowan University
Methods
Destabilization
MgH2 and TiH2 were chosen to destabilize NaBH4. Destabilizing NaBH4 with a simple hydride involves
combing a 1:1 molar ratio of NaBH4 and the simple hydride and then ball milling for 5 min. with a 5:4 mill ball
to powder ratio. The samples were then heated to varying degrees, starting at 500°C and going up to 650°C.
X-ray Diffraction (XRD) was used to test the composition the samples to determine if desorption was
achieved.
Nanostructure
Nanostructuring a material involves inserting NaBH4 into a MOF by dissolving the NaBH4 and MOF into THF
and subjecting it to vacuum pressure to evaporate the THF. What is left behind is the MOF with NaBH4
inserted into its pores. This has been experimentally tested to lower the desorption temperature of NaBH4, but
it is difficult to detect using XRD. Instead we tested the use of Raman Spectroscopy to determine if it could be
used to identify the different components of a material that had been inserted into a MOF.