Temperature effect on hydrogen generation by the reaction of γ-Al2O3-modified Al powder with distilled water

Article abstract of DOI:10.1111/j.1551-2916.2005.00534.x

The effect of temperature on the reaction of γ-Al₂O ₃-modified Al powders with distilled water was investigated. It was found that by increasing the temperature up to 40°C, the hydrogen generation speed can be enhanced one to two ord

Full text of DOI:10.1111/j.1551-2916.2005.00534.x

J. Am. Ceram. Soc., 88 [10] 2975–2977 (2005)
DOI: 10.1111/j.1551-2916.2005.00534.x
r 2005 The American Ceramic Society
ournal
J
Temperature Effect on Hydrogen Generation by the Reaction of
c-Al2O3-Modified Al Powder with Distilled Water
Zhen-Yan Deng,w Yu-Fu Liu, Yoshihisa Tanaka, Hong-Wang Zhang, Jinhua Ye, and Yutaka Kagawa*,z
National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
The effect of temperature on the reaction of c-Al2O3-modified
Al powders with distilled water was investigated. It was found
that by increasing the temperature up to 401C, the hydrogen
generation speed can be enhanced one to two orders of magni-
tude relative to that at room temperature (181C). X-ray analyses
and transmission electron microscopy observations revealed that
the reaction by-product at 401C is bayerite (Al(OH)3), which is
chemically neutral. The present results imply that slightly in-
creasing the temperature is an effective way to get the target
hydrogen generation speed.
on the reaction of g-Al2O3-modified Al powders with distilled
water is presented.
II. Experimental Procedure
The fabrication of g-Al2O3-modified Al powders has been re-
ported in detail in previous works.7 The Al and Al(OH)3 pow-
ders were mixed and then pressed under a unidirectional
pressure of 120 MPa to form the green compacts. The com-
pacts were heated and sintered at a temperature of 6001C for 1
h. The sintered porous specimens were very weak and were me-
chanically crashed into powders and sieved using a 100 mesh
nylon sieve. As the decomposition of Al(OH)3 at elevated
temperature produced g-Al2O3 phase,8–10 these powders are
g-Al2O3-modified Al particle powders (see Fig. 2), referred to
as GMAPs hereafter. Different Al(OH)3 content in the starting
mixture produced different GMAPs with different g-Al2O3
content.
The hydrogen generation experiment of Al with water was
carried out at room temperature (181C), 401 and 501C, using 0.5 g
GMAPs suspended in 270 mL of distilled water in a pyrex glass
cell. The gases evolved were determined by the thermal conduc-
tivity detector (TCD) 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 uncertainties were about 0.05%.11 An X-ray dif-
fractometer (XRD; Model No. RINT2000, Rigaku Co., Tokyo,
Japan) was used to analyze the phases in as-received GMAPs
and those reacted at different temperatures. Transmission elec-
tron microscopy (TEM) was used to observe the morphologies
and analyze the phases of as-received GMAPs and those after
reaction with distilled water.
I. Introduction
YDROGEN is an ideal fuel because it is lightweight, of high
chemical energy and its oxidation product (water) is envi-
H
ronmentally benign. However, storage and transportation of
hydrogen remains a problem. To solve this problem, most re-
searchers pay attention to hydrogen-storage materials. But stor-
age and release of hydrogen by these materials need some
conditions such as special temperature and pressure,1,2 that
would increase some extra components in the application. These
extra parts considerably increase the volume and cost of acces-
sory for small fuel cells applied in portable devices such as video
cameras and notebook computers, etc.3 One way to overcome
the shortcomings is to use the direct reaction of metals with
water to generate hydrogen.1
The alkali metals Li, Na, and K can directly react with water
and generate hydrogen. However, alkali metals are expensive
and the reaction by-products are strong alkalis, which are dif-
ficult to deal with in the application. Among other metals, Al is
of particular interest because of its light atomic weight, high
electron density, and abundance in the earth. In fact, it has a
long history in the study of the reaction of metal Al with acid
and basic aqueous solutions to generate hydrogen for portable
fuel cells.4,5 However, the direct reaction of metal Al with pure
water is difficult because of a dense passive oxide film that cov-
ers the metal Al surface when fresh Al is exposed to an oxidation
environment.6
III. Results and Discussion
Figure 1 shows the evolution of the gases from the distilled wa-
ter containing GMAPs with different compositions at room
temperature, 401 and 501C, where 0.5 g of GMAPs are used in
each test. In addition to hydrogen, no other gases were detected
during the reaction. At room temperature, it is clear that
the amount of generated hydrogen increases with increasing
g-Al2O3 content in the GMAPs. When the g-Al2O3 content in
the GMAPs increases, the Al particle surfaces covered by g-
Al2O3 increase.7 By increasing the temperature up to 401C, the
hydrogen generation speed was enhanced one to two orders of
magnitude relative to that at room temperature. The hydrogen
generation speed was further enhanced when the temperature
was up to 501C, and 55%–70% of metal Al in the GMAPs was
consumed within B7 h. This implies that at allowable working
temperature for different portable applications, the hydrogen
generation speed could be easily adjusted by slightly changing
the reaction temperature. At 401 and 501C, the hydrogen gene-
ration is also related to the g-Al2O3 content in the GMAPs, be-
cause the amount of hydrogen generated by the GMAP with
In a previous work,7 we have reported that metal Al powders
could completely react with distilled water at room temperature
under atmospheric pressure and generate hydrogen by Al par-
ticle surface modification using fine g-Al2O3 phase through a
ceramic processing procedure. However, the hydrogen genera-
tion speed at room temperature is not high enough to satisfy the
practical requirements. In this work, the effect of temperature
H. Du—contributing editor
Manuscript No. 20314. Received March 16, 2005; approved April 18, 2005.
*Member, American Ceramic Society.
wAuthor to whom correspondence should be addressed. e-mail: zydeng6403@yahoo.
com
zInstitute of Industrial Science, The University of Tokyo, Tokyo, Japan.
2975

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Vol. 88, No. 10
30 wt% Al+70 wt% γ-Al2O3
63 wt% Al+37 wt% γ-Al2O3
80 wt% Al+20 wt% γ-Al2O3
12000
10000
8000
6000
4000
2000
0
Al
γ-Al O
2
3
Bayerite
50°C
+
d
c
40°C
+
+
+
RT
b
a
0
2
4
6
8
Time (hours)
Fig. 1. H2 evolution from distilled water using the g-Al2O3 modified Al
particle powders with different compositions at room temperature, 401
and 501C.
20
40
60
80
100
63 wt% Al137 wt% g-Al2O3 (triangle marks) is always larger
than that by the GMAP with 80 wt% Al120 wt% g-Al2O3
(square marks). It should be mentioned that because the total Al
amount in the GMAP with 30 wt% Al170 wt% g-Al2O3 is
limited, at 401 and 501C its generated hydrogen amount is small-
er than those by the other two GMAPs shown in Fig. 1. More-
over, it was found that no obvious hydrogen generation
occurred when the pure Al powder was put in 751C distilled
water for 10 h under atmospheric pressure, indicating that the
surface modification for Al powder is the key to changing its
corrosion resistance.
Figure 2 shows the typical X-ray diffraction patterns of as-
received GMAPs and of those after reaction at room tempera-
ture, 401 and 501C. As has been confirmed in our previous
paper,7 all the phases at the passive layers on original Al particle
surfaces have been transformed into g-Al2O3 phase after surface
modification. After reaction with distilled water at room tem-
perature, there is no obvious phase change of the GMAP with
63 wt% Al137 wt% g-Al2O3, although the previous work7 re-
vealed that the reaction by-product of GMAPs with distilled
water at room temperature was boehmite (AlOOH). One pos-
sible reason is that the present room temperature by-product
boehmite was too small to be detected. But it is clear that the
main diffraction peak of metal Al becomes weak after reaction
at room temperature. At 401 and 501C, the diffraction peaks of
metal Al disappear and a new phase bayerite (Al(OH)3) appears.
The diffraction peak strength of bayerite increases with increas-
ing temperature from 401 to 501C, indicating that at 401 and
501C, metal Al reacted with water and generated hydrogen and
bayerite
2θ (degree)
Fig. 2. X-ray patterns for the g-Al2O3 modified Al particle powders
with 63 wt% Al137 wt% g-Al2O3: (a) as-received, (b) after reaction with
distilled water at room temperature for 22.7 h, and (c) after reaction with
distilled water at 401C for 6.8 h and (d) after reaction with distilled water
at 501C for 7.0 h.
nology.12 The chemical energy of hydrogen is 142 MJ/kg and the
efficiency of the fuel cell can reach 50%–60%.1 It can be un-
derstood that a 5 W video camera can work for B8 h using 20 g
of the GMAP with 80 wt% Al120 wt% g-Al2O3 shown in
Fig. 1.
The typical morphologies and corresponding selected area
electron diffraction patterns of original Al powder, as-received
GMAP, and those after reaction at room temperature and 401C
are shown in Fig. 3. It is clear that the original Al particle sur-
faces are smooth and dense (Fig. 3(a)). After modification, the
Al particle surfaces became loose and a part of the Al particles in
as-received GMAP was obviously covered by the fine g-Al2O3
grains produced by the decomposition of Al(OH)3 (Fig. 3(b)).
After the GMAP reacted with distilled water at room temper-
ature, there were some new fine wire-like grains on Al particle
surfaces and no dense passive layers were formed; these wire-like
grains were confirmed to be the reaction by-product boehmite
(see the right-corner inset in Fig. 3(c)), which is consistent with
our previous observation.7 At the temperature of 401C, the grain
morphology changed substantially relative to that of the as-re-
ceived GMAP, and the grain shape looked like a rectangular
billet (Fig. 3(d)), indicating that most of metal Al was consumed
and transformed into bayerite. Moreover, the grain morph-
ologies and phase compositions at 501C are almost the same
as those at 401C.
3
2
Al þ 3H2O ! AlðOHÞ3þ H2 "
(1)
This reaction produces 3.7 mass% hydrogen (weight ratio of
generated H2 to Al and H2O). In fuel cell application, if the
water produced by the fuel cell is redirected to GMAPs, then the
H2 generation amount increases to 11.1 mass%. The above re-
action by-product bayerite is chemically neutral8 and could be
reduced to metal Al for recycling by molten electrolytic tech-
Because the continuous reaction of metal Al with distilled
water is related to the existence of fine g-Al2O3 grains on Al
particle surfaces, and these loose g-Al2O3 grains play a key role
in increasing the pitting and assist the ion and vacancy trans-
portation on Al particle surfaces,7,13 it seems that increasing the

October 2005
Communications of the American Ceramic Society
2977
Fig. 3. Transmission electron microscopy micrographs and selected area electron diffraction patterns showing the morphologies and phases of
(a) original Al powder, (b) as-received g-Al2O3 modified Al particle powders (GMAP) with 63 wt% Al137 wt% g-Al2O3 (the right-corner inset is the
diffraction pattern of g-Al2O3), (c) the GMAP in (b) after reaction with distilled water at room temperature for 22.7 h (the right-corner inset is the
diffraction pattern of boehmite) and (d) the GMAP in (b) after reaction with distilled water at 401C for 6.8 h.
2A. M. Seayad and D. M. Antonelli, ‘‘Recent Advances in Hydrogen Storage in
Metal-Containing Inorganic Nanostructures and Related Materials,’’ Adv. Mater.,
16 [9–19] 765–77 (2004).
3H. Ozu, ‘‘Recent Development of Small Fuel Cells for Portable Electrical De-
vices,’’ Mater. Jpn., 42 [9] 617–20 (2003) (in Japanese).
reaction temperature slightly could considerably speed up these
processes. Moreover, just part of the Al particle surfaces in
GMAPs was covered by g-Al2O3 phase, as shown in Fig. 3(b),
because the Al(OH)3 particles retained their original shape after
decomposition.10 If the g-Al2O3 phase can be more uniformly
distributed on Al particle surfaces, the hydrogen generation
speed would be enhanced further at the tolerable elevated tem-
perature and at the same time, g-Al2O3 content in the GMAPs
would decrease.
4D. Belitskus, ‘‘Reaction of Aluminum with Sodium Hydroxide Solution as a
Source of Hydrogen,’’ J. Electrochem. Soc., 117 [8] 1097–9 (1970).
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J. Am. Ceram. Soc. 88 [4] 977–979 (2005).
IV. Conclusion
8R. B. Bagwell and G. L. Messing, ‘‘Critical Factors in the Production of Sol–
Gel Derived Porous Alumina,’’ Key. Eng. Mater., 115, 45–63 (1996).
9Z. Y. Deng, T. Fukasawa, M. Ando, G. J. Zhang, and T. Ohji, ‘‘High-Surface-
Area Alumina Ceramics Fabricated by the Decomposition of Al(OH)3,’’ J. Am.
Ceram. Soc., 84 [3] 485–91 (2001).
In this work, hydrogen generation by the reaction of g-Al2O3-
modified Al powders with distilled water at 401 and 501C was
studied. The results showed that slightly increasing the temper-
ature up to 401 and 501C could considerably increase the hy-
drogen generation speed, depending on the g-Al2O3 content in
the modified Al powders. The present results indicated that the
hydrogen generation speed could be conveniently adjusted in
the practical portable application in the tolerable temperature
region.
10Z. Y. Deng, T. Fukasawa, M. Ando, G. J. Zhang, and T. Ohji, ‘‘Bulk Alumina
Support with High Tolerant Strain and its Reinforcing Mechanisms,’’ Acta Ma-
ter., 49 [11] 1939–46 (2001).
11Z. G. Zou, J. H. Ye, K. Sayama, and H. Arakawa, ‘‘Direct Splitting of Water
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&
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¨