Role of modification agent coverage in hydrogen generation by the reaction of Al with water

Article abstract of DOI:10.1111/j.1551-2916.2010.03875.x

Previous works indicated that Al particle surfaces could be modified by fine γ-Al₂O₃ grains, which can be used as a hydrogen-generation material, where the fine γ-Al₂O₃ grains were produced by the decomposition of the Al(OH)₃ phase in the mixture. In this work, commercially available γ-Al₂O ₃ powder was directly used as the modification agent and mixed with Al powder and heat treated at an elevated temperature. It was found that the modified Al powder produced by directly using γ-Al₂O ₃ has an obvious shorter time for complete hydrogen generation than that using Al(OH)₃-produced γ-Al₂O₃. Microstructure analyses revealed that directly using γ-Al ₂O₃ powder has a better coverage of fine γ-Al ₂O₃ grains on Al particle surfaces than the Al(OH) ₃-produced γ-Al₂O₃. This implies that a uniform distribution of modification agents on Al particle surfaces is an important factor for the Al-water reaction dynamics.

Full text of DOI:10.1111/j.1551-2916.2010.03875.x

J. Am. Ceram. Soc., 93 [9] 2534–2536 (2010)
DOI: 10.1111/j.1551-2916.2010.03875.x
r 2010 The American Ceramic Society
ournal
J
Role of Modification Agent Coverage in Hydrogen Generation by the
Reaction of Al with Water
w
Zhen-Yan Deng, Wen-Hui Liu, and Wei-Zhuo Gai
Energy Materials & Physics Group, Department of Physics, Shanghai University, Shanghai 200444, China
Yoshio Sakka and Jinhua Ye
National Institute for Materials Science, Ibaraki 305-0047, Japan
Zhong-Wen Ou
Analysis Center of Engineering Building Materials, Logistical Engineering University, Chongqing 400041, China
Previous works indicated that Al particle surfaces could be
modified by fine c-Al O grains, which can be used as a hydro-
which creates environmental pollution concerns in the applica-
tion. Metals Ga, In, Bi, Sn, etc. are expensive, which increase
the cost considerably.
2
3
gen-generation material, where the fine c-Al O grains were
2
3
9,10
produced by the decomposition of the Al(OH) phase in the
Deng et al.
found that metal Al particle surfaces could be
3
mixture. In this work, commercially available c-Al O powder
modified by fine g-Al O grains using a ceramic-processing pro-
2
3
2
3
was directly used as the modification agent and mixed with Al
powder and heat treated at an elevated temperature. It was
found that the modified Al powder produced by directly using
c-Al O has an obvious shorter time for complete hydrogen
cedure. The modified Al powder continuously reacted with wa-
ter and generated hydrogen under an ambient condition.
Relative to other ways of activating metal Al, ceramic modifi-
cation of metal Al powder is simple and cheap. In the above
2
3
9
,10
generation than that using Al(OH) -produced c-Al O . Micro-
works,
position of the Al(OH)
able g-Al O was directly used as the modification agent. The
the fine g-Al
2
O
3
grains were produced by the decom-
3
2
3
structure analyses revealed that directly using c-Al O powder
3
phase. In this work, commercially avail-
2
3
has a better coverage of fine c-Al O grains on Al particle sur-
2
3
2
3
faces than the Al(OH) -produced c-Al O . This implies that a
uniform distribution of modification agents on Al particle sur-
faces is an important factor for the Al–water reaction dynamics.
effect of modification agent coverage on Al–water reaction dy-
namics was investigated.
3
2
3
II. Experimental Procedure
I. Introduction
Highly pure Al (99.9% purity, 7.29 mm, High Purity Chemical
Co., Tokyo, Japan), Al(OH)
3
(99.99% purity, 2.5 mm, High Pu-
LOBAL environmental change and temperature rise have
spurred scientists to develop new clean and renewable en-
rity Chemical Co.), and g-Al O (99.99% purity, surface area
2
3
G
2
1
90 m /g, Taimei Chemical Co., Nagano, Japan) were used in
the present experiment. Two kinds of mixtures of Al1Al(OH)
and Al1g-Al were prepared in a highly pure ethanol solu-
tion and ball milled for 24 h using high purity Al O balls, then
ergy technologies. Hydrogen is an ideal fuel, because its oxida-
tion product (water) is environmentally benign. However,
storage and transportation of hydrogen remain a problem,
due to its low boiling point (ꢀ2521C) and very poor compress-
ibility. In the past few years, different methods have been de-
veloped to solve this problem, e.g. hydrogen-storage materials
3
2 3
O
2
3
dried and sieved using a 100-mesh nylon sieve. The mixtures
were pressed under a unidirectional pressure of 75 MPa to form
the green compacts. The compacts were heat treated at a heating
rate of 11C/min and held at a temperature of 6001C in vacuum
for 1 h. The heat-treated compacts were mechanically crushed
into powder and sieved using a 100-mesh nylon sieve. As
1–3
and hydrogen-generation materials. However, there is no fea-
sible way for the large-scale use of hydrogen for vehicles, sta-
tionary, and mobile applications so far.
Recently, metal Al entered the scope of the research due to its
light atomic weight, high electron density, and cheap cost rela-
tive to other hydrogen-generation materials, e.g. NaBH
the decomposition of Al(OH)
3
at elevated temperature produced
phase, both of the starting mixtures finally became
2 3
O -modified Al powders, referred to as GMAPs hereaf-
11
4
. How-
the g-Al
the g-Al
O
2 3
4
ever, the direct reaction of metal Al with pure water is difficult
because of a dense passive oxide film that covers the metal Al
surface. Several ways were adopted to make metal Al react with
aqueous solution or water and generate hydrogen. For example,
NaOH solution was used to react with metal Al powder and
generate hydrogen. Alloying Al by doping B20 wt% Ga, In, Bi,
Sn, etc. could make metal Al continuously react with pure water
ter. The final GMAPs prepared by two different starting mixtures
have the same composition of 70 vol% Al130 vol% g-Al O .
2
3
The hydrogen-generation experiment of two GMAPs was
carried out at a temperature of 221C. 0.2 g of GMAP was used
in each test, which was suspended in 270 mL of distilled water in
a Pyrex glass cell. At the beginning of the experiment, the glass
cell was evacuated to a low vacuum of 0.03 bar. The gases
evolved were determined by the thermal conductivity detector
gas chromatograph (Model No. GC-8A, Shimadzu, Kyoto,
Japan), which was connected to the glass-made gas-circulating
line attached to the Pyrex glass cell. The measurement uncer-
5
–8
and generate hydrogen. However, NaOH is a strong alkali,
D. De—contributing editor
1
2
tainties were about 0.05%. The schematic representation of
the present hydrogen-generation equipment can be found in
Hara et al.
Manuscript No. 27565. Received February 12, 2010; approved April 18, 2010.
Author to whom correspondence should be addressed. e-mail: zydeng@shu.edu.cn
w
13
2
534

September 2010
Rapid Communications of the American Ceramic Society
2535
starting mixtures could completely react with water and generate
hydrogen. However, the complete reaction time of the GMAP
prepared from the Al1g-Al O mixture (referred to as
G-GMAP hereafter) is obviously shorter than that from the
Al1Al(OH) mixture (referred to as A-GMAP hereafter). It
3
took B34.1 and 69.8 h for G-GMAP and A-GMAP to com-
pletely react with water, respectively. The main difference in the
reaction dynamics between G-GMAP and A-GMAP is at the
beginning of the reaction. The induction time for the beginning
of the reaction for A-GMAP is B35 h, but the corresponding
induction time for G-GMAP is just B3 h. After the beginning
of the reaction, the hydrogen-generation rate of A-GMAP and
G-GMAP is almost the same.
Figure 2 shows TEM micrographs of original Al powder, as-
received A-GMAP, and G-GMAP, respectively. It can be seen
that pure Al particle surfaces are smooth and dense. After mod-
2 3
ification, the Al particle surfaces were covered by fine g-Al O
grains and not as smooth as pure Al particles, as clearly shown
in Fig. 2(c). TEM photos in Fig. 2 indicated that there is a more
1
00
2
3
a
b
8
6
4
2
0
0
0
0
0
0
20
40
60
80
Reaction Time (hours)
Fig. 1.
H
2
evolution from distilled water at 221C using GMAPs pre-
and (b) Al1
2 3
O , respectively, where both GMAPs have the same composition
pared from the starting mixtures of (a) Al1Al(OH)
g-Al
3
2 3
uniform coverage of g-Al O on the Al particle surfaces of G-
GMAP than that of A-GMAP. In fact, just part of the Al par-
ticle surfaces of A-GMAP was covered by fine g-Al O grains,
e.g. the part indicated by arrow in Fig. 2(b). The nonuniform
2 3
of 70 vol% Al130 vol% g-Al O and 0.2 g of GMAPs was used in each
2
3
test.
coverage of g-Al in A-GMAP originates from the large sizes
2 3
O
of Al(OH)3 particles, because the Al(OH)3 particles retained
their original morphology after decomposition at an elevated
temperature. In this case, the rigid contact between Al(OH)
X-ray diffractometry (Model No. RINT2000, Rigaku Co.,
Tokyo, Japan) was used to analyze the phases in GMAPs and
those after reaction with water. Transmission electron micros-
copy (TEM) was used to observe the morphologies of GMAPs.
1
4
3
particles and Al particles in the starting mixture confines the
coverage of the Al(OH) -produced g-Al O grains on Al particle
3
2
3
surfaces.
Figure 3 shows the X-ray patterns of as-received A-GMAP
and G-GMAP and those after reaction with water. It can be
III. Results and Discussion
Figure 1 shows the gas evolution from the distilled water at 221C
containing the GMAPs with the composition of 70 vol% Al130
vol% g-Al O prepared from two different starting mixtures. In
seen that all the Al(OH)
g-Al phase after heat treatment. The g-Al
by Al(OH)
method, which is almost the same as that of commercial g-Al O
2 3
3
phase have decomposed into the
phase produced
has a surface area of 187 m /g measured by the BET
O
2 3
2 3
O
2
2
3
3
addition to hydrogen, no other gases were detected during the
reaction. It is clear that both of the GMAPs from two different
powder used in this work. Figure 3 indicates that bayerite
(
a)
1µm
0.2µm
0.4µm
(
b)
(c)
Fig. 2. Transmission electron micrographs of (a) the original Al powder and as-received GMAPs prepared from the starting mixtures of
b) Al1Al(OH) and (c) Al1g-Al , respectively.
(
3
2 3
O

2
536
Rapid Communications of the American Ceramic Society
Vol. 93, No. 9
2 3
g-Al O
grains on Al particle surfaces in G-GMAP leads to a
Al
-Al O
2
3
Bayerite
short induction time for the beginning of the reaction. This is
why G-GMAP has a shorter complete hydrogen-generation
time than A-GMAP. In this way, if the coverage of modifica-
tion agents is improved further, the complete hydrogen-gener-
ation time would become even shorter.
d
IV. Conclusions
In this work, commercially available g-Al
rectly used to modify Al particle surfaces. The modified Al
powder produced by directly using g-Al has an obvious
shorter time for complete hydrogen generation than that using
Al(OH) -produced g-Al in the previous work. Microstruc-
ture analyses indicated that directly using g-Al powder has a
better coverage of fine g-Al grains on Al particle surfaces
than the Al(OH) -produced g-Al O , leading to a shorter in-
2 3
O powder was di-
c
2 3
O
3
2 3
O
2 3
O
2 3
O
b
a
3
2
3
duction time for the beginning of the reaction. This implies that
a uniform distribution of modification agents on Al particle
surfaces is important for the fast Al–water reaction.
Acknowledgments
Zhen-Yan Deng would like to thank the financial supports of the Research
Fund for the Doctoral Program of Higher Education of China (No.
2
0093108110003), Shanghai Leading Academic Discipline Project (project num-
20
40
60
(degree)
80
ber S30105), Pujiang Talent Project (07pj14040), ‘‘211 Project,’’ and Innovation
Fund of Shanghai University.
2
Fig. 3. X-ray patterns for (a) the as-received GMAP prepared from the
starting mixture of Al1Al(OH) , (b) that in (a) after reaction with water
at 221C for 69.8 h, (c) as-received GMAP prepared from the starting
mixture of Al1g-Al , and (d) that in (c) after reaction with water at
21C for 34.1 h.
3
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