Multi-shaped amorphous alloy Ni-B: Ultrasonically aided complexing-reduction preparation, catalytic ability for NaBH4 hydrolysis yielding H2 gas

Article abstract of DOI:10.1002/zaac.201300336

The multi-shaped amorphous alloy (Ni-B) powders were prepared by complexing reduction route using sodium borohydride (NaBH₄) as reductant with assistance of ultrasonic wave. The selected complexants, i.e. water, ammonia, salicylic acid, and eth

Full text of DOI:10.1002/zaac.201300336

ARTICLE
DOI: 10.1002/zaac.201300336
Multi-shaped Amorphous Alloy Ni-B: Ultrasonically Aided
Complexing-reduction Preparation, Catalytic Ability for NaBH4 Hydrolysis
Yielding H2 Gas
Jun Zhang,[a] Chengxuan Li,[a] Lili Li,[a] Xigang Du,[a] Bangcai Song,[a] and Hang Xu[a]
Keywords: Amorphous materials; Alloys; Ni-B; Complexing reduction; NaBH4; Hydrogen
Abstract. The multi-shaped amorphous alloy (Ni-B) powders were the as-prepared Ni-B powders all belong to amorphous alloy with vari-
prepared by complexing reduction route using sodium borohydride able element contents, and the Ni-B sample prepared from EDTA com-
(NaBH4) as reductant with assistance of ultrasonic wave. The selected plexation, possessing the best fineness and dispersity, has the strongest
complexants, i.e. water, ammonia, salicylic acid, and ethylene diamine
catalytic activity. The mean apparent activation energy of the hydroly-
tetraacetic acid (EDTA) possess sequentially escalating complexation sis reaction is 64.90 kJ·mol–1. The NaBH4 concentration has little im-
ability. The chemical composition and shapes of the product samples
obtained under different conditions were characterized by X-ray pow-
pact on hydrogen generation rate, implying that the catalytic hydrolysis
of NaBH4 solution should be the pseudo zero-order reaction. Keeping
der differaction, selected area electron diffraction, and transmission the NaOH content at below 5% could inhibit the hydrolysis of NaBH4
electron microscope. The influence of reaction conditions such as the solution, but the NaOH contents from 10% to 15% will significantly
types of Ni-B, temperatures, NaBH4 concentrations, and sodium hy- promote the hydrolysis rate of NaBH4. The hydrolysis reaction mecha-
droxide (NaOH) content on the hydrogen generation rate of hydrolysis nisms, especially the effect of NaOH content on the hydrolysis reaction
of NaBH4 solution were investigated in detail. The results show that
were also analyzed.
By now, the catalysts reported, which are suitable for hydro-
gen generation by NaBH4 hydrolysis, are mainly noble metal
ones, such as Pt[4,5] and Ru[6] with different supported form
and loadings, as well as double noble metal catalysts loaded
on LiCoO2 surface[7]. Besides, some non-noble metal chlorides
including FeCl2, CoCl2, NiCl2[8], and Raney Ni, Raney Co,
and relevant alloy MgxNi[9,10], etc., have also been intensively
studied and used for the controllably catalytic hydrolysis of
the borohydride. However, for catalysts mentioned above there
more or less exist such shortcomings as high price, low ac-
tivity, advance activation, unstable hydrogen releasing rate,
and inconvenience of separation and regeneration, and so on.
In contrast, amorphous alloy, which is endowed with distin-
guishing features of higher activity, lower cost, and easier re-
cycling, has attracted lots of attention as a new type of catalyst
in the last decades.
1 Introduction
Sodium borohydride (NaBH4), a coordination hydride, is be-
coming an emerging and compelling hydrogen production ma-
terial with high specific energy in recent years due to its high
theoretical hydrogen storage of up to 10.6 wt%.[1] The hydro-
gen production by NaBH4 hydrolysis possesses such advan-
tages as high hydrogen gas purity, controllable gas release rate,
high security, and recycling of byproduct, etc., already being
used as the preferred hydrogen source of proton exchange
membrane fuel cell (PEMFC). The hydrolysis of NaBH4 in
aqueous solution generates hydrogen gas and sodium hypobor-
ate along with the heat release and the reaction rate is largely
affected by temperature and pH value. Under the absence of
catalysts, the relationship[2,3] among half-life period (t1/2), tem-
perature (T) and pH follows such an empirical formula: lgt1/2
= pH–(0.034T–1.92). The reaction half-life period could reach
400 d under normal temperature and higher pH value (pHϾ8),
which is an appropriate reaction rate and can basically satisfy
many actual applications. However, further studies confirm
that heterogeneous catalytic hydrolysis of NaBH4 solution
should be more preferable in order to achieve quick start and
controlled hydrogen evolution.
2 Experimental Section
2.1. Chemicals and Instruments
Nickel acetate [Ni(CH3COO)2·4H2O], sodium borohydride (NaBH4),
sodium ethylene diamine tetraacetic acid (C10H14N2O8Na2·2H2O,
EDTA), ammonia (NH3·H2O), salicylic acid (C6H4OHCOOH) and so-
dium hydroxide (NaOH) are all analytically pure reagents and directly
used without further purification. The phase state and chemical compo-
sition of the products were analyzed by X-ray powder diffractometer
(XRD) (Advance-D8, Bruker, Germany) with Cu-Kα radiation (λ =
0.15406 nm) and inductively coupled plasma optical emission spec-
trometer (ICP-OES) (Optima 2100DV, Perkin–Elmer, US), respec-
* Prof. J. Zhang, Ph. D.
Fax: 86-379-64232193
E-Mail: j-zhang@126.com; zhjabc@mail.haust.edu.cn
[a] Chemical & Pharmaceutical Engineering School
Henan University of Science and Technology
263 Kaiyuan Avenue
Luoyang 471023, Henan Province, P. R.China
456
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Multi-shaped Amorphous Alloy Ni-B
tively. Transmission electron microscopy (TEM) (H800, Hitachi,
Japan) and scanning electron microscopy (SEM) (JSM-6330F, JEOL,
Japan) were employed for the morphological observation and selected
electronic diffraction measurement. The chemical valence states of
elements on the surfaces of the Ni-B samples were determined with
an X-ray photoelectron spectrometer (XPS) (PHI5400, Perkin-Elmer,
US). A hermetically sealed magnetic stirring apparatus (Variomag,
Thermo-Fisher, USA) was underwater placed in a waterbath to agitate
the solution.
persion peak at around 45°(2θ), which belongs to the charac-
teristic diffraction peak of amorphous alloy Ni-B.[11] No other
impurity peaks appear, implying the relatively high purity of
as-prepared Ni-B product. Moreover, further studies confirm
that the XRD patterns of all the other Ni-B samples prepared
under the given conditions were similar to Figure 1, indicating
that the target product, namely amorphous alloy Ni-B, could
be achieved according to the above experimental design. The
other XRD patterns except that of Ni-B-1 are not shown herein
for brevity.
2.2 Preparation of Amorphous Alloy Ni-B Powders
A Ni2+ solution (20 mL, 0.2500 mol L–1) was mixed with EDTA solu-
tion (20 mL, 0.1750 mol L–1) whilst stirring, and the pH value of the
mixture was adjusted to 3.5 through dropwise adding of HCl
(4 mol L–1). The resulting pale blue transparent solution was transfer-
red into a flask, which in advance was put in 298 K water bath and
ultrasonically treated (45 KHz, 100 W) for 30 min. Meanwhile, NaBH4
(0.02 mol) was dissolved in a NaOH solution (10 mL, 0.01 mol L–1),
whose temperature was preset at about 273 K. Afterwards the alkaline
NaBH4 solution was added into the flask, and the reaction immediately
started. Until no bubbles escape the reaction was terminated. The sus-
pension liquid product was centrifuged, washed 3–5 times using water
and absolute ethanol in turn and finally kept in absolute ethanol to
avoid oxidation before use. The black solid powders separated by cen-
trifugation should be vacuum dried at 333 K for 6 h, which was labeled
as Ni-B-1.
Figure 1. XRD pattern of Ni-B-1 amorphous alloy.
3.2 The Morphological Analysis of the Amorphous Alloy
Ni-B Powders
The TEM images of Ni-B-1, Ni-B-2, Ni-B-3, and Ni-B-4
are displayed in Figure 2. It can be seen that Ni-B-1 particles,
prepared by using the strongest complexant EDTA, have ball-
like shape with average grain diameter of less than 40 nm.
What is more, these particles possess good dispersity, rela-
tively uniform size, clear interface, and hardly any aggrega-
tion. The morphology of Ni-B-2 particles is obviously different
from that of Ni-B-1 due to adopting salicylic acid as com-
plexant, whose complexing ability is weaker than EDTA. In
this case, the particles with a little reunion are linked to each
Taking the similar tactic, through separately substituting salicylic acid,
ammonia, and water for the above complexant EDTA, the correspond-
ing black powders could also be obtained, which was sequentially lab-
eled as Ni-B-2, Ni-B-3, and Ni-B-4.
2.3 The Evaluation method of Catalytic activity of Ni-B
Samples
Into the NaBH4 solution with a given concentration was added a cer-
tain amount of NaOH to maintain appropriate alkalinity, followed by
the addition of the as-prepared Ni-B sample with different mass. The
hydrogen generation volume in unit time from the hydrolysis reaction
under different conditions was recorded in detail, so as to evaluate the
catalytic activity of the corresponding Ni-B sample. In particular, a
three-necked round-bottomed flask with proper capacity, equipped
with a thermometer and a gas collecting device in the two side necks,
respectively, was kept in a glassy thermostatic waterbath. A reasonable
amount of catalyst Ni-B and alkaline NaBH4 solution was successively
added into the flask through the middle neck, and simultaneously agi-
tated by a waterproof type magnetic stirrer. Once the reaction started,
the hydrogen generation volumes in different time intervals should be
accurately recorded.
Results and Discussion
3.1 Phase Analysis of As-prepared Amorphous Alloy Ni-B
Powders
The phase structure of as-prepared Ni-B powders by using
the given four complexants under different conditions was ana-
lyzed by X-ray powder diffraction, and the corresponding
XRD pattern concerning Ni-B-1 was shown in Figure 1. The
Figure 2. TEM and SAED images of Ni-B amorphous alloy:
XRD pattern definitely displays only one wide-shoulder dis- (A)Ni-B-1, (B)Ni-B-2, (C)Ni-B-3, (D)Ni-B-4.
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J. Zhang, C. Li, L. Li, X. Du, B. Song, H. Xu
ARTICLE
other just like a line, and the average diameter increases to rich nickel and electron-deficient boron in the alloy.[13] Based
70 nm. The complexing ability of ammonia further weakens, on the above experimental facts it is not difficult to judge that
so its corresponding product, i.e. Ni-B-3 sample, is endowed there should exist more electron transfers in the case of
with the reticular appearance, and with more serious aggrega- Ni-B-1.
tion and larger mean diameter of 100 nm. Among the four
complexants the water has the weakest complexing ability, and
its resulting Ni-B-4 sample shows much more serious aggrega-
3.4 The Evaluation of Catalytic Activity
tion and largest average diameter of 150 nm. The four inserted
annular SAED images also verify the amorphous feature of the
four kinds of Ni-B.
3.4.1 The Catalytic Activity of the Different Ni-B Samples
The catalytic capacities of the different types of Ni-B sam-
ples were evaluated by the hydrolysis of NaBH4 solution and
the experimental results are shown in Figure 3. The hydrolysis
reaction condition was designed as follows: reaction tempera-
ture 303 K, NaBH4 concentration 0.0749 mol·L–1 (mass frac-
tion 0.28%), NaOH content 0.0100 mol·L–1 (mass fraction
0.04%), and Ni-B dosage 0.6667 g·L–1. As seen from Figure 3,
within the first 20 min of the hydrolysis reaction, the hydrogen
gas yield per unit time, i.e. hydrogen generation rate, catalyzed
by Ni-B-1, Ni-B-2, Ni-B-3, and Ni-B-4, decreases sequentially.
In comparison with those of Ni-B-2, Ni-B-3, and Ni-B-4, the
hydrogen generation rate by using Ni-B-1 increases by 26%,
43% and 64%, respectively. The required time that reaches a
maximum hydrogen generation volume (35 mL) for Ni-B-1,
Ni-B-2, Ni-B-3, and Ni-B-4 is quite different (20 min, 30 min,
40 min, and 60 min, respectively). If no any catalyst (Ni-B)
was added, the NaBH4 aqueous solution could only hydrolyze
spontaneously, releasing only 1 mL hydrogen gas in 50 min,
which stands in sharp contrast to that catalyzed by Ni-B pow-
ders. Theoretically, the catalytic activity of the Ni-B samples
largely depends upon the number of active site of surface Ni
atoms. Owing to unique microstructure of the amorphous alloy,
the Ni atoms at electron-rich state could provide more active
sites.[14] The XPS analysis results in Table 1 reveal that the
enriching electron ability of Ni atoms in Ni-B-1, Ni-B-2, Ni-
B-3, and Ni-B-4 successively decreases, and this sequence
agrees with the catalytic activity of the Ni-B samples shown
in Figure 3.
The reduction process of Ni2+ by NaBH4 is a drastically
exothermic reaction, and the reaction product Ni-B is at the
thermodynamically metastable state.[12] The heat release dur-
ing the reduction process could heat up the reaction system,
intensifying the collision between the nascent product par-
ticles, and resulting in aggregation. On the other side, the for-
mation of complex ions between complexant and Ni2+ ions
inevitably cause the decrease of concentration of free Ni2+ in
the solution, leading to slowdown of the reduction reaction
rate, and weakening the collision and aggregation between na-
scent particles. The complexing ability or binding capacity of
the complexants with Ni2+ successively declines in sequence
of EDTA, salicylic acid, ammonia, and water, whose order is
evidently in accordance with the agglomerate degree of Ni-B
particles observed by TEM.
3.3 The Chemical Composition and Valence State of the
Amorphous Alloy Ni-B Powders
The fresh Ni-B samples just separated from the absolute eth-
anol and dried in vacuo, were analyzed by ICP-AES and XPS,
so as to determine chemical composition and valence state.
The corresponding results are collected in Table 1. As can be
found from Table 1, the nickel contents in the four Ni-B sam-
ples are slightly different, following such an ascending order
from Ni-B-1, Ni-B-2, Ni-B-3, to Ni-B-4. This result could also
be explained according to the aforesaid strong-to-weak se-
quence of the complexants. The XPS analysis results reveal
that the average electron binding energy of Ni2p in the
Ni-B samples is 852.6 eV, coinciding basically with the stan-
dard electron binding energy of the metal nickel (852.3 eV).
By comparison with the standard electron binding energy of
B
1s in metalloid B (187.2 eV), it is easily found that each bind-
ing energy of B1s in four Ni-B samples has shown positive
shift. From Ni-B-1 to Ni-B-4, the positive shift values are
1.2 eV, 1.0 eV, 0.9 eV, and 0.3 eV, respectively, suggesting the
evident existence of interaction between Ni and B atoms in the
amorphous alloy Ni-B. Some of electrons in boron atoms
transfer to nickel atoms, resulting in the formation of electron-
Figure 3. Hydrogen generation rate of NaBH4 hydrolysis catalyzed by
different Ni-B.
Table 1. Atomic molar ratios and energy peaks of the Ni-B samples.
Atomic molar ratio
XPS energy peak /eV
B1s
Ni2p
3.4.2 Effect of NaBH4 Concentration on Hydrogen Yield
Ni-B-1
Ni-B-2
Ni-B-3
Ni-B-4
Ni73.6B26.4
188.4
188.2
188.1
187.5
853.1
852.7
852.1
852.5
Ni74.2B25.8
Ni74.9B25.1
Ni75.5B24.5
The Ni-B-1 sample, possessing the strongest catalytic ac-
tivity among the four amorphous alloys, was used as catalyst
to evaluate the effect of different NaBH4 concentrations on
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Multi-shaped Amorphous Alloy Ni-B
hydrogen yield. Under such conditions as reaction temperature were systematically studied. As shown in Figure 5, the hydro-
303 K, NaOH content 0.0100 mol·L–1 and Ni-B-1 dosage gen generation rates all increases with the rise of temperatures.
0.6667 g·L–1, the hydrogen generation rate was investigated, Maximum hydrogen generation volume reaches 40 mL within
and the results are shown in Figure 4. The hydrogen generation 15 min at 318 K, while the maximal volume is only 5.5 mL at
volume is 20 mL in the first 20 min reaction time, if the 298 K within the same time period. For the low temperatures
NaBH4 concentration is kept at 0.28% (mass fraction, the less than 318 K, the maximum hydrogen generation volumes
same below); similarly, in the same time span the hydrogen all decline in different degrees, in comparison with the results
generation volume reaches 25 mL and 28 mL, respectively, as obtained at 318 K. Before reaching the maximum value, the
the NaBH4 concentration rises up to 1% and 5%. These results hydrogen generation volumes at different temperatures linearly
indicate that in low content range (less than 5%) the rising of ascend with the hydrolysis time, but the variation of hydrogen
NaBH4 concentration could observably promote the hydrogen generation volume tends to be flat after the maximum value.
generation rate. However, while the NaBH4 concentration con- In addition, it also can be seen from Figure 5 that the hydroly-
tinues to rise up to 10% and 15%, the hydrogen generation sis reaction rate is relatively slow at 298 K. In the initial 5
volumes within 20 min are only 29 mL and 30 mL, respec- min, there exists an induction period, which quickly disappears
tively, showing relatively smaller increments. On the whole, with the rise of temperature, and the reaction rate evidently
with the NaBH4 concentration rising from 0.28% to 15%, the speeds up after exceeding the induction period. As previously
maximum hydrogen generation volume increases from mentioned, the hydrolysis of NaBH4 can be regarded as zero-
34.5 mL to 40.5 mL. In particular, the maximum hydrogen order reaction, so the rate constant (k) can be calculated ac-
generation volume increases by only 1 mL when the NaBH4 cording to dynamics principle and equations. Based on Arrhe-
concentration increases from 5% to 15%. Figure 4 shows that nius equation, plotting ln(k) vs. the reciprocal of temperature
the hydrogen generation rates under different NaBH4 concen- (K), Figure 6 could be obtained. The apparent activation en-
trations reveal very little variation in the same time, which ergy (Ea) could be calculated to be 64.9 kJ·mol–1. Under the
corresponds to the kinetics feature of zero-order reaction[15]
.
same conditions, the apparent activation energies of NaBH4
As a reasonable inference, solubility of the byproduct (NaBO2) hydrolysis catalyzed by Ni and CoB were reported to be
from the hydrolysis reaction is 28.2 g at room temperature, 71 kJ·mol–1 and 68.87 kJ·mol–1,[18,19] respectively. By contrast,
which corresponds to the theoretical NaBH4 concentration of the apparent activation energy catalyzed by Ni-B-1 reduces by
8.5%.[16,17] Hence, under the higher NaBH4 concentration 6.1 kJ·mol–1 and 3.97 kJ·mol–1, respectively.
(e.g. 5%) the rapid hydrolysis reaction inevitably produces a
mass of byproduct NaBO2, meanwhile brings some water
away along with the escape of H2 gas. Such a double action
will make NaBO2 rapidly reach saturation point, and deposit
on the surface of the catalyst, weakening the catalytic activity.
On the other side, with the precipitation of NaBO2, the hydro-
lysis solution becomes thicker and thicker, impeding the mass
transfer, and further resulting in the decline of the hydrolysis
reaction rate.
Figure 5. Hydrogen generation rate of NaBH4 hydrolysis catalyzed by
Ni-B-1 at different temperatures.
Figure 4. Hydrogen generation rate of NaBH4 hydrolysis catalyzed by
Ni-B-1 under different NaBH4 concentrations.
3.4.3 Effect of Temperature on Hydrogen Yield
With the Ni-B-1 dosage and NaOH content in the solution
kept at 0.6667 g·L–1 and 0.0100 mol·L–1, respectively, the hy-
drogen generation capacity from hydrolysis of 0.0749 mol·L–1
Figure 6. Plot of lnk vs. 1/T for NaBH4 hydrolysis catalyzed by
NaBH4 solution in the temperature range from 298 to 318 K Ni-B-1.
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J. Zhang, C. Li, L. Li, X. Du, B. Song, H. Xu
ARTICLE
3.4.4 Effect of NaOH Concentration on Hydrogen Yield
gradually declines prior to the “threshold” (e.g. 5%) of the
NaOH concentration. However, after exceeding the “thresh-
old” concentration, the hydrogen generation rate shows a sig-
nificant rise. Therefore, the two-step reaction mechanism could
provide a reasonable explanation for the action of NaOH.
With the Ni-B-1 dosage fixed at 0.6667 g·L–1, NaBH4 con-
centration at 0.0749 mol·L–1 and hydrothermal temperature at
303 K, the hydrogen generation rates from NaBH4 hydrolysis
under different NaOH contents involving 0.04%, 1%, 5%,
10%, and 15% were investigated. Just as seen from Figure 7,
as the NaOH content is 0.04% the hydrogen generation vol-
ume reaches 14 mL within 15 min, but the volume drops to
only 6 mL, while the NaOH content is 1%. Furthermore, con-
tinuing to elevating the NaOH content to 5% results in the
bigger decline of hydrogen generation volume, that is, drop-
ping to 2.5 mL. However, the hydrogen generation rate dra-
matically increases to 27.7 mL per 15 min if the NaOH content
rises to 10%. In the case of 15% NaOH content, the hydrogen
generation rate is 27 mL per 15 min, almost remaining un-
changed, compared with 10% NaOH content. The above ex-
perimental results clearly show that the role of NaOH not only
promote but also inhibit the hydrolysis reaction, and the NaOH
content seems to have a strange “threshold”.
4 Conclusions
The four kinds of amorphous alloy (Ni-B-1, Ni-B-2,
Ni-B-3, and Ni-B-4) were prepared by ultrasonically assisted
complexing-reduction approach using EDTA, salicylic acid,
ammonia, and water as complexants. Through the characteriza-
tion and catalytic activity evaluation for these Ni-B samples,
it could be concluded: (1) The as-prepared Ni-B samples were
verified to be all non crystal matters. The complexing ability
largely affects the chemical composition and phase state of
the Ni-B products. The stronger the complexing ability of the
complexant is, the smaller the Ni-B particle size is, the higher
the dispersity is. (2) With EDTA used as complexant, the re-
sulted product Ni-B-1 has the highest catalytic capacity for the
hydrogen production from NaBH4 hydrolysis. Compared with
Ni-B-2, Ni-B-3, and Ni-B-4, not only the hydrogen generation
volume from NaBH4 hydrolysis catalyzed by Ni-B-1 within
20 min increases by 26%, 43%, and 64%, respectively, but
also it reaches the maximum hydrogen generation volume in
the first place. (3) Increasing the reaction temperature benefits
the rising of the hydrolysis reaction rate. The apparent acti-
vation energy of the hydrolysis reaction is calculated to be
64.90 kJ·mol–1. (4) The NaBH4 concentration has little influ-
ence on the hydrogen generation rate, inferring to the chemical
kinetics characteristics of zero-order reaction. (5) Keeping the
NaOH content less than 5% will inhibit the hydrolysis of
NaBH4, while maintaining the NaOH content at 10% to 15%
will dramatically promote the hydrogen generation rate.
Figure 7. Hydrogen generation rate of NaBH4 hydrolysis catalyzed by
Ni-B-1 under different NaOH contents.
The influencing mechanisms of NaOH concentration on
catalytic hydrolysis of NaBH4 solution must be quite complex,
and different explanations were suggested elsewhere.[20,21]
Based on the above experimental results, the following two-
Acknowledgements
–
step reaction mechanisms are here proposed: BH4 + H2O Ǟ
The authors gratefully acknowledge the financial support from the
BH3 + H2(g) + OH– (I); BH3 + OH– + H2O Ǟ BO2– + 3H2(g) National Natural Science Foundation of China (21076063, 21006057),
Henan Provincial Development Foundation for Science and Technol-
ogy (102102210170), Project for Development of Science and Tech-
nology of Luoyang (1101030A), the Key Laboratory Construction Pro-
ject for Chemical Engineering of Mineral Resources of Luoyang
(1003016A).
(II). When NaOH concentration is lower than the threshold,
reaction (I) should be the control step for the whole hydrolysis
process; increasing the concentration of OH– is not in favor of
the reaction (I) and thus inhibit the whole hydrolysis reaction.
Otherwise, if the NaOH concentration is higher than the
threshold, the reaction (II) may dominate the hydrolysis pro-
cess; increasing the concentration of OH– should benefit reac-
tion (II) and significantly improve the hydrogen generation
rate. Theoretically, the molar quantity of hydrogen generation
of reaction (II) should be three times of that of the reaction (I).
On the other side, the rapid development of reaction (II)
inevitably leads to the formation and aggregation of the by-
product NaBO2, which has small solubility in the aqueous
solution. The precipitation of NaBO2 on surface of the catalyst
particles would decrease mass transfer, and impair catalytic
activity. On basis of the above analysis from the both aspects,
it is not difficult to infer that the hydrogen generation rate
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Received: July 9, 2013
Published Online: October 2, 2013
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