- MgH2 proved to be an effective destabilizing agent for NaBH4, lowering its desorption temperature to 500°C, while TiH2 showed no destabilization effect. Nanostructuring NaBH4 using a MOF was unsuccessful according to Raman spectroscopy data. USAXS data indicated the hydrides have a highly porous fractal structure, and that the MOF contains NaBH4 within or surrounding it. Future work will include modifying ratios and methods to further lower desorption temperatures with destabilization and achieve 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
X­Ray Diffraction (XRD) is a useful technique that uses X­rays 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 X­Ray 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.
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 X­ray
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 cm­1
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 (q­vector), 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 MOF­only sample has scattering intensity of less than
0.01 cm­1
sr1
while the MOF sample containing the
NaBH­4 (as well as NaBH­4 along) shows scattering
intensity above 0.1 cm­1
sr1
at the same scattering angle
(q­vector).
•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,
446­447, 23­27(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. “X­ray imaging with ultra­small­angle X­ray scattering as a contrast
mechanism.” Journal of Applied Crystallography. 0021­8898(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, 619­623(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, 19134­19140(2007).
Acknowledgements
We wish to thank Mr. Christopher Bennett for help in learning how to operate the glovebox and
Analysis of NaBH4 for Hydrogen Storage
Nicholas S. Riffitts, Joseph Iannello, and Tabbetha Dobbins
Dept. of Physics & Astronomy, College of Science & Mathematics, Rowan University
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Methods
Destabilization
MgHMgH22 and TiHand TiH22 were chosen to destabilize NaBHwere chosen to destabilize NaBH44. Destabilizing NaBH. Destabilizing NaBH44 with a simple hydride involveswith a simple hydride involves
combing a 1:1 molar ratio of NaBHcombing a 1:1 molar ratio of NaBH44 and the simple hydride and then ball milling for 5 min. with a 5:4 mill balland 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.to powder ratio. The samples were then heated to varying degrees, starting at 500°C and going up to 650°C.
X­ray Diffraction (XRD) was used to test the composition the samples to determine if desorption wasX­ray Diffraction (XRD) was used to test the composition the samples to determine if desorption was
achieved.achieved.
Nanostructure
Nanostructuring a material involves inserting NaBHNanostructuring a material involves inserting NaBH44 into a MOF by dissolving the NaBHinto a MOF by dissolving the NaBH44 and MOF into THFand MOF into THF
and subjecting it to vacuum pressure to evaporate the THF. What is left behind is the MOF with NaBHand subjecting it to vacuum pressure to evaporate the THF. What is left behind is the MOF with NaBH44
inserted into its pores. This has been experimentally tested to lower the desorption temperature of NaBHinserted into its pores. This has been experimentally tested to lower the desorption temperature of NaBH44, but, but
it is difficult to detect using XRD. Instead we tested the use of Raman Spectroscopy to determine if it could beit 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.used to identify the different components of a material that had been inserted into a MOF.