Ammonium octahydrotriborate (NH4B3H8): New synthesis, structure,and hydrolytic hydrogen release

Article abstract of DOI:10.1021/ic2000987

A metathesis reaction between unsolvated NaB₃H₈ and NH₄Cl provides a simple and high-yield synthesis of NH ₄B₃H₈. Structure determination through X-ray single crystal diffraction analysis reveals weak N-H^δ+ - H ^δ- -B interaction in NH₄B₃H₈ and strong N-H^δ+- H^δ+-B interaction in NH ₄B₃H₈ 3 18-crown-6 3THF adduct. Pyrolysis of NH₄B₃H₈ leads to the formation of hydrogen gas with appreciable amounts of other volatile boranes below 160 °C. Hydrolysis experiments show that upon addition of catalysts, NH₄B ₃H₈ releases up to 7.5 materials wt % hydrogen.

Full text of DOI:10.1021/ic2000987

ARTICLE
pubs.acs.org/IC
Ammonium Octahydrotriborate (NH4B3H8): New Synthesis, Structure,
and Hydrolytic Hydrogen Release
Zhenguo Huang,† Xuenian Chen,†,‡ Teshome Yisgedu,† Edward A. Meyers,‡ Sheldon G. Shore,*,‡ and
Ji-Cheng Zhao*,†
†Department of Materials Science and Engineering and ‡Department of Chemistry, The Ohio State University, Columbus, Ohio 43210,
United States
S Supporting Information
b
ABSTRACT: A metathesis reaction between unsolvated NaB3H8 and
NH4Cl provides a simple and high-yield synthesis of NH4B3H8. Structure
determination through X-ray single crystal diffraction analysis reveals weak
NꢀHδþ- - -HδꢀꢀB interaction in NH4B3H8 and strong NꢀHδþ
—
H
δꢀꢀB interaction in NH4B3H8 18-crown-6 THF adduct. Pyrolysis of
3
3
NH4B3H8 leads to the formation of hydrogen gas with appreciable amounts
of other volatile boranes below 160 °C. Hydrolysis experiments show that
upon addition of catalysts, NH4B3H8 releases up to 7.5 materials wt %
hydrogen.
’ INTRODUCTION
crystallographic study of the structure; (3) thermal decomposi-
tion; and (4) interesting hydrogen release properties through
hydrolysis.
The safe and efficient hydrogen storage is a major barrier to
the use of hydrogen as a transportation fuel. Intensive efforts in
recent years have been focused on boron hydrides such as metal
borohydrides (Mg(BH4)2,1 NaBH4 ) and amine boranes
2
’ EXPERIMENTAL SECTION
4
(NH3B3H7,3 NH3BH3 ) for hydrogen storage because of their
General Procedures. All manipulations were carried out on a
high-vacuum line or in a glovebox filled with high purity nitrogen.
Solvents were dried over sodium/benzophenone and freshly distilled
prior to use. Ammonia (Matheson) was distilled from sodium immedi-
ately prior to use. NMR spectra were obtained on a Bruker Avance DPX
250 NMR. 11B NMR spectra were obtained at 80.3 MHz and externally
high hydrogen contents. Various catalysts have been investigated
to improve hydrogen release from these materials through either
thermal decomposition or hydrolysis. However, none of these
materials under investigation meets the multiple targets set forth
by the U.S. Department of Energy (DOE).
The great variety and distinct properties of boron compounds
prompt us to search for a compound that could satisfy the
requirements for hydrogen storage. To obtain a high hydrogen
capacity, it is essential to find a suitable combination of light-
weight cation and H-rich BmHn anion. High number of m
in BmHn leads to a lower hydrogen content and also greater
stability of the boron cluster.5 Ammonium octahydrotriborate,
NH4B3H8, has a high hydrogen content of 20.5 wt %. Unfortu-
nately, the first synthesis reported 40 years ago involves penta-
borane, B5H9, which is highly volatile and inflames violently upon
contact with air.6a,b There are two pentaborane-free patents, but
the procedures are complicated and require intermediate com-
pounds and large amounts of solvents.6c,d Probably because of
the lack of suitable syntheses, there have been little explorations
of its reactivities and properties in 40 years. Here we report (1) a
simple and efficient synthesis of this compound; (2) a
1
referenced to BF3 OEt2 in C6D6 at 0.00 ppm. H NMR spectra were
3
obtained at 250.1 MHz and referenced to THF-d8. Unsolvated NaB3H8
was prepared following the procedure recently developed in our lab.7
NH4Cl (Aldrich) was recrystallized from methanol. Mass spectra
of the gas released from the hydrolysis and thermal decomposition
were collected through a Balzer’s Quadstar 422 Quadrupole mass
spectrometer.
Synthesis of NH4B3H8. The prepared unsolvated NaB3H8 (634 mg, 10
mmol) reacted with NH4Cl (535 mg, 10 mmol) in liquid ammonia at
ꢀ78 °C. After 30 min stirring using a magnetic bar, ammonia was
removed and the flask was warmed to room temperature. The desired
NH4B3H8 was extracted using dry tetrahydrofuran (THF) followed by
pumping off THF right away, leaving a white powder, NH4B3H8 (555
Received: January 16, 2011
Published: March 15, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
Table 1. Crystallographic Information
empirical formula
formula weight
H12B3N
58.54
C16H44B3NO7
394.95
crystal system
space group
Z
orthorhombic
Cmcm
monoclinic
Pc
4
4
a, Å
7.1530(14)
8.2648(17)
8.3895(17)
90
16.407(3)
11.215(2)
13.841(3)
90
b, Å
c, Å
Figure 1. 1H NMR spectrum of NH4B3H8 recorded in THF-d8 at room
R, deg
β, deg
γ, deg
T, K
temperature. Inset is the 11B NMR spectrum.
90
107.76(3)
90
90
Hydrolytic H2 Release Measurements. In a two-neck flask
connected to a vacuum line, 1 mmol NH4B3H8 was mixed with 0.04
mmol CoCl2. After evacuating all the gases via dynamic vacuum, the flask
was sealed and 18 mmol water was injected. After the reaction comple-
tion, the flask was opened to a vacuum line, and the evolved gas passed
through a liquid nitrogen trap to isolate any non-hydrogen products,
including water. The hydrogen was then quantitatively measured using a
Toepler pump. About 8.80 mmol H2 was obtained through the reaction.
For catalyst screening, a gas buret was set up to measure the amount
of H2 gas and to determine the rates of H2 release.3a Pt/C (10 wt % Pt),
Ru/Al2O3 (5 wt % Ru), RuCl3, CoCl2, NiCl2, and FeCl3 were all tested
as received. For the catalyst loading, 1 mol % (with reference to
NH4B3H8) of noble metal (Pt or Ru) was loaded, while 4 mol % of
transition metal (Co, Ni or Fe) was employed.
150
150
V, Å3
Dcalcd (g cmꢀ3
μ (mmꢀ1
495.97(17)
0.784
2425.4(9)
1.082
)
3
)
0.038
0.079
λ, Å
0.71073
1617
0.71073
8313
no. reflns collected
no. unique reflns
R1 [I > 2σ (I)]a
wR2(all data)b
a R1 = ∑||Fo| ꢀ |Fc||/∑|Fo|. b wR2=[∑w(F2oꢀFc2)]2/∑w(Fo2)2]1/2
251 (Rint = 0.0245)
0.0370
4286 (Rint = 0.0258)
0.0420
0.1043
0.1153
mg, yield 95%). 11B NMR: (THF-d8) δ ꢀ29.9 ppm, 1H NMR (THF-
d8): NH4þ, δ 6.8 ppm; B3H8ꢀ, δ 0.2 ppm.
X-ray Crystallography. X-ray quality crystals of the NH4B3H8
3
’ RESULTS AND DISCUSSIONS
18-crown-6 THF adduct were grown from 1:1 (molar ratio) mixtures
3
A simple and efficient method has now been developed to
synthesize NH4B3H8 via a metathesis reaction between unsol-
vated NaB3H8 and NH4Cl in liquid ammonia (eq 1).
of NH4B3H8 and 18-crown-6 in THF. NH4B3H8 single crystals were
grown from anhydrous CH3CN. Caution! At room temperature, signs of
decomposition (bubbles) were observed after a few days for both the
NH4B3H8/18-crown-6/THF and NH4B3H8/CH3CN mixtures.
X-ray single crystal diffraction data were collected on a Nonius Kappa
CCD diffractometer which employs graphite-monochromated Mo KR
radiation (λ = 0.71073 Å). Because of the sensitivity of the compound,
single crystals were picked up from the mother solution in a nitrogen
filled glovebox and stored in Fomblin oil until data collection. A single
crystal coated with Fomblin oil was mounted on the tip of a glass fiber.
Unit cell parameters were obtained by indexing the peaks in the first 10
frames and refined by employing the whole data set. All frames were
integrated and corrected for Lorentz and polarization effects using the
DENZO-SMN package.8 Absorption correction for the structure was
accounted for by using SCALEPACK.8 The structure was solved
(Table 1) by direct method using the SHELXTL-97 (full-matrix least-
squares refinements) structure solution package.9 All nonhydrogen
atoms were located and refined anisotropically. Hydrogen atoms on
boron and nitrogen atoms were located and refined isotropically, and
other hydrogen atom positions were calculated by assuming standard
geometries.
NH4Cl þ NaB3H8 f NH4B3H8 þ NaCl
ð1Þ
This reaction proceeds rapidly, and the desired product can be
efficiently extracted using THF after removing the liquid ammo-
nia. Furthermore, the yield is ∼95%, higher than 79.5% reported
for the previous methods.6 The unsolvated NaB3H8 was pre-
pared via a route recently developed in our lab,7 which eliminates
the use of dangerous starting materials such as B2H6 and BF3
and enables a high yield. Therefore, a large-scale and simple
synthesis of NH4B3H8 is now possible.
The metathesis reaction has also been explored in several
other solvents, and it was found that the solvent had an influence
on the course of the reaction. In addition to NH4B3H8,
NH3B3H7 and other boron compounds were also observed for
the reaction in THF and DME, with the latter resulting in more
NH3B3H7.
The successful synthesis in liquid ammonia is corroborated by
the NMR spectrum (Figure 1). After extracting NH4B3H8 using
THF and then pumping off the THF immediately via dynamic
11
Thermal Decomposition Studies. Thermal stability of
NH4B3H8 was studied using a Mettler Toledo high-pressure differential
scanning calorimeter (DSC27HP) in an argon glovebox with a ramp rate
of 5 °C/min. Thermogravimetric analysis (TGA) was performed on a
Perkin-Elmer TGA 7 analyzer. Powder was loaded onto a quartz crucible
and heated to 400 °C at a heating rate of 5 °C/min under an Ar flow of
40 cm3/min. The gaseous decomposition products were semiquantified
through a calibrated vacuum line. After freezing out the gaseous products
at ꢀ196 °C, hydrogen content was determined; after removing hydro-
gen and then raising the temperature to ꢀ78 °C, diborane was
quantified; the residual product, pentaborane and borazine, were
analyzed after diborane was removed and temperature was raised to
∼25 °C.10
vacuum, pure desired product was obtained. NH4B3H8 exhibits a
11B NMR resonance at ꢀ29.9 ppm, which is assigned to B3H8
.
ꢀ 7
1
The H NMR spectrum of NH4B3H8 reveals the existence of
both NH4þ (6.8 ppm) and B3H8ꢀ (0.2 ppm).
The structures of NH4B3H8 and NH4B3H8 18-crown-
3
6 THF adduct were determined through single crystal X-ray
3
diffraction analysis. Selected bond distances and angles are given
in Tables 2 and 3, respectively. Figure 2 shows a separate ion pair
structure of NH4B3H8, with the shortest NꢀHδþ---HδꢀꢀB
distance being 2.37(3) Å, very close to the sum of van der Waals
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Inorganic Chemistry
ARTICLE
Table 2. Selected Bond Distances and Angles of H12B3Na
N(1)ꢀH(5)
0.85(3)
N(1)ꢀH(6)
0.79(4)
B(1)ꢀB(2)
1.779(2)
1.779(2)
1.475(18)
1.079(17)
1.813(3)
1.096(13)
1.137(17)
113(2)
B(1)ꢀB(2)#
B(1)ꢀH(4)
B(1)ꢀH(1)
B(2)ꢀB(2)#
B(2)ꢀH(3)
B(2)ꢀH(4)
H(5)ꢀN(1)ꢀH(6)
B(2)ꢀB(1)ꢀB(2)#
B(2)ꢀB(1)ꢀH(4)
B(2)#ꢀB(1)ꢀH(4)
B(2)ꢀB(1)ꢀH(1)
B(2)#ꢀB(1)ꢀH(1)
H(4)ꢀB(1)ꢀH(1)
B(1)ꢀB(2)ꢀB(2)#
B(1)ꢀB(2)ꢀH(3)
B(2)#ꢀB(2)ꢀH(3)
B(1)ꢀB(2)ꢀH(4)
B(2)#ꢀB(2)ꢀH(4)
H(3)ꢀB(2)ꢀH(4)
61.27(11)
39.5(7)
Figure 2. Crystal structure of NH4B3H8. B, pink; H, light gray; N,
blue.
100.8(7)
117.3(7)
117.3(7)
100.4(4)
59.37(5)
121.5(6)
108.5(7)
55.7(9)
115.0(9)
104.2(8)
a Symmetry transformations used to generate equivalent atoms. # = x, y, ꢀz
þ 3/2.
Table 3. Selected Bond Distances and Angles of C16H44B3NO7
Figure 3. Fragment of the NH4B3H8 18-crown-6 THF adduct. B,
pink; H, light gray; N, blue; O, red; C, gray.
3
3
N(1)ꢀH(2)
0.82(5)
0.92(4)
0.87(4)
0.99(6)
1.758(6)
1.796(7)
1.762(6)
1.14(4)
1.27(5)
1.10(4)
1.08(5)
1.41(4)
111(4)
N(1)ꢀH(1)
N(1)ꢀH(3)
since BꢀN compounds tend to have close NꢀHδþ---HδꢀꢀB
N(1)ꢀH(4)
contacts,12a as observed in NH3B3H7 and NH3BH3.12b This
3a
B(1)ꢀB(3)
structure differs from the reported metal octahydrotriborates,
where B3H8 can coordinate with a metal center such as for
Cr(B3H8)2,11c (CO)4Mn(B3H8),13 Mg(B3H8)2(Et2O)2,14 and
Ru(B3H8)(PPh3){κ3-HB(pz)3}.15
B(1)ꢀB(2)
B(2)ꢀB(3)
B(1)ꢀH(9)
B(1)ꢀH(15)
The molecular structure of NH4B3H8 18-crown-6 THF ad-
3
3
B(2)ꢀH(11)
duct is illustrated in Figure 3. Ammonium cation has been
B(2)ꢀH(12)
reported to connect to crown ether by three NꢀH O hydro-
3 3 3
B(3)ꢀH(16)
gen bonds between the hydrogen atoms of the ammonium and
the oxygen atoms of the crown ether.16 We likewise found similar
interaction present in NH4B3H8 18-crown-6 THF adduct.
H(2)ꢀN(1)ꢀH(3)
H(1)ꢀN(1)ꢀH(3)
H(2)ꢀN(1)ꢀH(4)
H(1)ꢀN(1)ꢀH(4)
B(3)ꢀB(1)ꢀB(2)
B(1)ꢀB(3)ꢀB(2)
B(3)ꢀB(2)ꢀB(1)
B(3)ꢀB(1)ꢀH(9)
B(3)ꢀB(1)ꢀH(10)
B(2)ꢀB(1)ꢀH(15)
B(1)ꢀB(3)ꢀH(16)
B(2)ꢀB(3)ꢀH(16)
B(1)ꢀB(3)ꢀH(15)
B(1)ꢀB(3)ꢀH(14)
108(3)
3
3
111(4)
There is another independent fragment in the asymmetric unit,
very similar to the one shown in Figure 3. The THF molecule is
packed into the structure with no interactions with other
moieties. The average NꢀO distance is 2.94 Å, longer than the
standard NꢀO hydrogen bond length (2.87 Å).17 The hydrogen
atom on nitrogen that is not involved in bonding to an oxygen
atom interacts with three terminal hydrogen atoms on the boron
triangle, with the closest NꢀHδþ---HδꢀꢀB distance of 1.92(5)
Å being shorter than 2.13(3) Å present in NH3B3H7 determined
by X-ray diffraction analysis,3a significantly less than the sum of
van der Waals radii between two hydrogen atoms, 2.4 Å.
110(4)
59.4(3)
61.3(3)
59.2(2)
121.4(18)
126(2)
115(2)
102.0(17)
40.6(17)
45.1(19)
115.2(18)
NH4B3H8 in pure and solid form is stable at room temperature
with no detectable signs of decomposition within one month. On
the contrary, the adduct decomposes slowly at room temperature
with the evolution of hydrogen gas. The poor stability of the adduct
is likely due to the stronger NꢀHδþ---HδꢀꢀB interactions.
radii between two hydrogen atoms, 2.4 Å. All other NꢀHδþ---
H
δꢀꢀB distances are more than 2.47 Å. This seems unusual
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Inorganic Chemistry
ARTICLE
Figure 5. 11B NMR spectra of 2 M aqueous solutions taken after (a) 1
day for NaBH4; (b and c) 1 day and 7 days for NH4B3H8. Inset is an
expanded spectrum of c. *, B5O6(OH)4ꢀ; †, B3O3(OH)h and
4
Figure 4. DSC and TGA curves of NH4B3H8 (5 °C/min).
B5O6(OH)h.
4
NH4BH4, an analogue of NH4B3H8, decomposes at ꢀ78 °C in
THF.18 This is in stark contrast to the slow degradation of
NH4B3H8 in THF at ambient conditions. Since both compounds
contain the same cation, the difference is likely due to the weaker
hydridic Hδꢀ of B3Hh compared to that of BH4ꢀ. This is
8
consistent with the findings that for boron hydrides the higher
number of boron atoms in the structure, the less hydridic the
hydrogen is.19
NH4B3H8 has a high hydrogen content, 20.5 wt %. Unfortu-
nately, thermal decomposition analysis shows that this com-
pound gives off 10 wt % hydrogen below 160 °C, but with
appreciable amounts of diborane, pentaborane, and borazine
(Supporting Information). DSC and TGA results (Figure 4)
collectively indicate that melting and decomposition take place
simultaneously at 120 °C, with a substantial weight loss at this
temperature. The presence of the boranes results in a ∼70% final
weight loss. It has been reported that NH3BH3 gives off the first
equivalent H2 below 120 °C and further releases hydrogen at
higher temperature but with a small fraction of borazine.20
Compared with NH3BH3, NH4B3H8 produces less hydrogen
and more undesired volatile compounds below 160 °C. Thus,
NH4B3H8 is probably not a suitable candidate for hydrogen
storage through thermal decomposition.
Hydrolytic studies, however, have demonstrated that NH4B3H8
has advantages over NaBH42 and NH3BH3,4c,d the most studied
chemical hydrides for hydrogen storage via hydrolysis. At room
temperature, NH4B3H8 is more soluble in water (>45 wt %
through visual observation) than NH3BH3 (26 wt %21) and
NaBH4 (35 wt %22). The lower solubility significantly limits the
theoretical hydrogen density of the respective system to 5.1 wt %
for NH3BH3 and 7.5 wt % for NaBH4. Quantitative measurements
of H2 released via hydrolysis using a Toepler pump and gas buret
showed that upon adding catalysts, 1 mmol NH4B3H8 releases a
near theoretical value of 8.80 mmol H2. Based on eq 2, therefore,
this system has a high theoretical hydrogen weight density [wt % =
H2/(NH4B3H8 þ H2O)] of 10.8 wt %.
Figure 6. Hydrogen evolution at room temperature from an aqueous
NH4B3H8 solution (molar ratio of NH4B3H8:H2O being 1:18) contain-
ing 10 wt % Pt/C (1 mol % Pt); 5 wt % Ru/Al2O3 (1 mol % Ru), RuCl3
(1 mol % Ru), CoCl2 (4 mol % Co), NiCl2 (4 mol % Ni), and FeCl3 (4
mol % Fe). Molar ratios are referenced to NH4B3H8.
solution with a 1:18 molar ratio of NH4B3H8 to H2O, which
represents a material density of 4.6 wt % H, the commercially
available 10 wt % Pt/C catalyst (1 mol % Pt) shows the best
catalytic activity, with complete hydrolysis in less than 30 min.
RuCl3 also displayed excellent catalytic activity, and this is likely
associated with the in situ formation of Ru(0) as indicated by the
formation of a black powder, which was also observed during
hydrolysis of both NaBH4 and NH3BH3.4c However, 5 wt %
2
Ru/Al2O3 (1 mol % Ru) is much less active. The difference is
probably associated with the degree of the dispersed catalytic
sites. Lower-cost transiton metal catalysts were also explored in
our study, and fairly good catalytic activity was observed for
CoCl2. With 4 mol % loading of CoCl2, full hydrolysis was
complete in about 100 min. A black powder appeared instantly
when CoCl2 was brought into contact with an aqueous
NH4B3H8 solution, suggesting the formation of cobalt boride
(Supporting Information) as found during the hydrolysis of
NaBH4.2 NiCl2 is less effective and the full hydrolysis requried
∼200 min.
cat:
NH4B3H8ðsÞ þ 6H2OðlÞ
s
f
NHþðaqÞ þ 3BOꢀðaqÞ
4
2
The “BO2ꢀ” product shown in eq 2 is only a hypothetical
formulation, with the actual borate products of these reactions
depending upon the final solution concentration and pH.3a
The 11B NMR spectrum (Figure 7) of the catalyzed hydrolysis
solution of NH4B3H8 and H2O (1: 18 ratio) reveals one broad
peak centered at 16 ppm which is likely associated with B3O3-
þ 2HþðaqÞ þ 9H2ðgÞ
ð2Þ
In addition, unlike NaBH4, which is stable only in strong
alkaline solutions,2 an aqueous NH4B3H8 solution is reasonably
stable as shown by 11B NMR studies (Figure 5). At 28 °C, for the
same molar concentration, that is, 2 M, 11B NMR studies show
that more than 50% of NaBH4 decomposed over a day, while less
than 10% of NH4B3H8 decomposed over a week.
ꢀ
(OH)4 and B5O6(OH)4ꢀ, along with another sharp peak
ꢀ 23
situated at around 0 ppm that is also due to B5O6(OH)4
.
Hydrolytic studies have shown that upon adding catalysts
NH4B3H8 rapidly releases pure H2 (Figure 6). For an aqueous
Similar products were also formed during the hydrolysis of
NH3B3H7.3a
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ARTICLE
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Figure 7. 11B NMR spectrum of the catalyzed hydrolysis solution
(NH4B3H8: H2O being 1: 18).
When an aqueous solution with 1:10 molar ratio of NH4B3H8
to H2O was subject to hydrolysis catalyzed by 4 mol % of CoCl2,
full hydrolysis was achieved in ∼200 min, which corresponds to a
production of 7.5 wt % H. The U.S. DOE recently modified the
vehicular hydrogen storage targets to 4.5 wt % by 2010, 5.5 wt %
by 2015, and 7.5 wt % for the ultimate.24 NH4B3H8 thus could be
a potential candidate to meet the 2010 target.
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Calculations of the standard heat of hydrolysis from the
standard enthalpies of formation indicate that H2 release from
NH4B3H8 is much less exothermic (5.43 kcal/mol H2, Support-
ing Information) than from either NaBH4 (14.9 kcal/mol H2),
NH3BH3 (12.7 kcal/mol H2), or NH3B3H7 (18.9 kcal/mol
H2).3a The less exothermic nature favors NH4B3H8 over the
other candidates from the standpoint of heat management and
system design.
As in the cases of NaBH4, NH3BH3, and NH3B3H7, the
formation of borates may affect the performance of the catalysts
if the borate precipitates cover the active sites. It should be noted
that the removal and transportability of the borates depend on
the starting materials and reaction conditions,25 and thus can be
improved accordingly. Regeneration of these compounds from
the borates has been challenging, but progress has been made in
the regeneration of spent fuel back into NH3BH3.26 The final
utility of NH4B3H8 as a chemical hydrogen storage material will
also hinge on the development of an efficient “off-board”
regeneration of NH4B3H8.
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’ ASSOCIATED CONTENT
S
Supporting Information. Structural information, calcu-
b
lation of the heat of the hydrolysis, mass spectra of gas from
hydrolysis and thermal decomposition. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(19) Parry, R. W.; Edwards, L. J. J. Am. Chem. Soc. 1959, 81, 3554.
(20) Hu, M. G.; Geanangel, R. A.; Wendlandt, W. W. Thermochim.
Acta 1978, 23, 249.
Corresponding Authors
*E-mail: zhao.199@osu.edu (J.-C.Z.), shore.1@osu.edu (S.G.S.).
(21) Brockman, A.; Zheng, Y.; Gore, J. Int. J. Hydrogen Energy 2010,
35, 7350.
(22) Rohm and Haas. The Sodium Borohydride Digest; 2003; p 8.
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ified vehicular hydrogen storage targets; https://www1.eere.energy.
gov/hydrogenandfuelcells/storage/pdfs/targets_onboard_hydro_
storage.pdf.
’ ACKNOWLEDGMENT
This work was funded by the U.S. Department of Energy,
Office of Energy Efficiency and Renewable Energy (EERE)
under Contract No. DE-FC3605GO15062.
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