Synthesis of loofah sponge carbon supported bimetallic silver-cobalt nanoparticles with enhanced catalytic activity towards hydrogen generation from sodium borohydride hydrolysis

Article abstract of DOI:10.1016/j.jallcom.2014.11.135

We demonstrate a functionalized carbonaceous material derived from the hydrothermal carbonization of natural loofah sponge can be served as an effective scaffold for anchoring bimetallic AgCo nanoparticles (NPs). The resulting loofah sponge carbon (LSC) supported AgCo NPs (LSC/AgCo) exhibits excellent performance for the catalytic hydrolysis of NaBH₄ towards hydrogen generation. It is experimentally proved that the existed AgCo NPs mainly contribute to the catalytic activity, while the employed LSC support make them more effective in LSC/AgCo catalytic systems. The catalytic activities of the LSC/AgCo catalysts are also strongly dependent on the Ag/Co ratio, where LSC/Ag_0.1Co_0.9 is most active among all of the catalysts, and even more than five times that of monometallic LSC/Co, revealing that the Ag and Co compositions in LSC/AgCo catalysts show excellent synergy to catalyze NaBH₄ hydrolysis for hydrogen generation. The present experimental study provides a promising pathway for the economical and sustainable implementation of biomass for the chemical hydrogen storage.

Full text of DOI:10.1016/j.jallcom.2014.11.135

Accepted Manuscript
Synthesis of loofah sponge carbon supported bimetallic silver-cobalt nanopar-
ticles with enhanced catalytic activity towards hydrogen generation from so-
dium borohydride hydrolysis
Lunhong Ai, Xiaomin Liu, Jing Jiang
PII:
S0925-8388(14)02783-2
DOI:
http://dx.doi.org/10.1016/j.jallcom.2014.11.135
JALCOM 32689
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To appear in:
Journal of Alloys and Compounds
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Revised Date:
Accepted Date:
15 September 2014
30 October 2014
21 November 2014
Please cite this article as: L. Ai, X. Liu, J. Jiang, Synthesis of loofah sponge carbon supported bimetallic silver-
cobalt nanoparticles with enhanced catalytic activity towards hydrogen generation from sodium borohydride
hydrolysis, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.11.135
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Synthesis of loofah sponge carbon supported bimetallic
silver-cobalt nanoparticles with enhanced catalytic activity
towards hydrogen generation from sodium borohydride
hydrolysis
∗
Lunhong Ai, Xiaomin Liu, Jing Jiang
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of
Chemistry and Chemical Engineering, China West Normal University, Nanchong 637002, P.R.
China
Abstract
We demonstrate a functionalized carbonaceous material derived from the hydrothermal
carbonization of natural loofah sponge can be served as an effective scaffold for anchoring
bimetallic AgCo nanoparticles (NPs). The resulting loofah sponge carbon (LSC) supported AgCo
4
NPs (LSC/AgCo) exhibits excellent performance for the catalytic hydrolysis of NaBH towards
hydrogen generation. It is experimentally proved that the existed AgCo NPs mainly contribute to
the catalytic activity, while the employed LSC support make them more effective in LSC/AgCo
catalytic systems. The catalytic activities of the LSC/AgCo catalysts are also strongly dependent
on the Ag/Co ratio, where LSC/Ag0.1Co0.9 is most active among all of the catalysts, and even
more than five times that of monometallic LSC/Co, revealing that the Ag and Co compositions in
4
LSC/AgCo catalysts show excellent synergy to catalyze NaBH hydrolysis for hydrogen
generation. The present experimental study provides a promising pathway for the economical
∗
Corresponding author. Tel./Fax: +86 817 2568081.
E-mail address: 0826zjjh@163.com (J. Jiang)
1

and sustainable implementation of biomass for the chemical hydrogen storage.
Keywords: Nanoparticles; Catalyst; Hydrogen generation; Sodium borohydride; Hydrolysis
1. Introduction
The extensive utilization of traditional fossil fuels causes severe environmental problem and
energy crisis. This major concern drives the increased demand for the exploration of the new
clean energy sources to meet the sustainability of human society [1, 2]. Hydrogen appears to be
one of most ideal and cleanest energy sources, which is considered to be a promising candidator
for a leading energy source in the future, due to its high gravimetric energy density, ideal
combustion efficiency and non-toxicity. However, the efficient and safe hydrogen storage is still
4
a critical issue for the practical implementation. Sodium borohydride (NaBH ) with high
-
3
gravimetric density (10.8 wt%) and volumetric hydrogen density (113 kg·m ) has been regarded
as an attractive candidate for hydrogen storage [3, 4], which can supply pure hydrogen by
4 2 2 2
room-temperature hydrolysis reaction (NaBH + 2H + 4H ↑). However, a
O → NaBO
favourable catalyst is required to accelerate this hydrolysis reaction in a controllable manner for
practical applications. Among a wide variety of available catalysts, noble metals such as Pt and
Pt-based alloys show unbeatable catalytic activity. However, the high cost and low abundance of
noble metals and alloys restrict their widespread application. Therefore, it is of great interest to
design and fabricate cost-effective alternatives to precious and low abundant Pt catalyst to gain a
4
sustainable hydrogen production from the NaBH hydrolysis reaction.
Cobalt is much more abundant than precious metals, which has emerged as an interesting
non-noble metal for its catalytic ability toward hydrogen generation. Particularly, it has been
recently reported that Co-based bimetallic systems are catalytically active toward the NaBH
4
2

hydrolysis for hydrogen generation, due to the combined properties of the two individual metals
derived from the electronic effects and geometric effects [5-7]. For example, CoPd bimetallic
nanoparticles (BNPs) obtained by
a unique solution phase synthesis showed the
composition-dependent activity for the hydrolysis and methanolysis of ammonia borane at room
temperature [8, 9]. The Co35Pd65 and Co48Pd52 BNPs were the most active catalyst in the
hydrolysis and methanolysis of ammonia borane, respectively. Other Co-based alloy catalysts
such as M@Co (M =Au [10] and Cu [11]) explored by Xu’s group also showed a significantly
higher catalytic activity than their monometallic counterparts. In addition, to further enhance the
catalytic activity, the robust support should be introduced to protect BNPs against dissolution and
aggregation. Cheng et al. systematically investigate a number of graphene-supported BNPs
catalysts and found that these supported catalytic systems exhibited the enhanced hydrogen
generation rates with respect to free BNPs [12-15]. Xu et al. have developed several remarkable
BNPs catalysts by anchoring them on the porous metal-organic frameworks (MOFs), and
observed the interesting synergistic catalysis phenomenon [16-19]. Therefore, combining the
designable BNPs and the effective support to the obtainable synergistic catalysis should be a
desirable strategy to achieve the enhanced catalytic efficiency and dramatically lower the
application cost.
Inspired our recent study on the cost-effective biomass-derived catalysts [20-22], we herein
report the economical and efficient bimetallic catalytic systems that can be fabricated by a
carbonaceous material derived from the hydrothermal carbonization of natural loofah sponge.
The loofah sponge carbon (LSC) supported AgCo NPs (LSC/AgCo) show superior performance
4
for catalyzing hydrolysis of NaBH toward hydrogen generation. Combining with Ag
3

significantly enhances the catalytic activity of Co and the catalytic activity of LSC/AgCo can be
improved by controlling their compositions, where the optimum activity is observed for
LSC/Ag0.1Co0.9. By taking advantage of structural properties, the LSC/Ag0.1Co0.9 also exhibits
more remarkable activity than that of free Ag0.1Co0.9 NPs. The present experimental study
provides an effective pathway for the economical and sustainable implementation of biomass for
the chemical hydrogen storage.
2. Experimental
2.1. Materials
3 2 2 3 4
Co(NO ) ·6H O, AgNO , NaBH , and NaOH were purchased from Kelong Chemical
Reagents Company (Chengdu, China) and used without further purification. All chemicals used
in this study were of commercially available analytical grade.
2.2. Hydrothermal synthesis of LSC
The loofah sponges were directly obtained from a local farm (Huafeng town, Nanchong City,
China). The carbonaceous sponges were prepared by a hydrothermal carbonization method using
loofah sponges as the carbon source. The loofah sponge was cut into different sizes and put into
a Teflon-lined stainless-steel autoclave and hydrothermal treated at 180 °C for 18 h. After that,
the loofah sponge carbon (LSC) was collected, washed with distilled water several times, and
dried in vacuum at 60 °C for 24 h.
2.3. Fabrication of LSC/AgCo catalysts
AgCo BNPs supported on LSC were fabricated by the chemical reduction during the catalytic
4
hydrolysis of NaBH . In a typical experiment of LSC/Ag0.1Co0.9, 0.01 g LSC, 0.18 mmol
3 2 2 3
Co(NO ) ·6H O and 0.02 mmol AgNO were added in 4.5 mL deionized water kept in a flask.
4

4
After ultrasonicating for about 15 min, 4.5 mL alkaline solution containing 0.5 g NaBH and 0.5
g NaOH were rapidly added into flake. AgCo BNPs were formed on LSC and the catalytic
4
hydrolysis of NaBH started immediately. To find the composition-dependent activity,
x
LSC/Ag Co1-x (x = 0, 0.1, 0.2, 0.3, 0.5, and 1) catalysts with various Ag/Co ratios were
synthesized by varying the concentration of Ag and Co salts in initial solution, where x
represents the molar portion of silver and the total molar amount of (Ag + Co) was kept at a
constant of 0.2 mmol.
2.4. Characterization
The X-ray diffraction (XRD) measurements were recorded on a Rigaku Dmax/Ultima IV
diffractometer with monochromatized Cu Kα radiation (λ = 0.15418 nm). The morphology was
observed with a JEOL 6700-F scanning electron microscope (SEM) and transmission electron
microscope (TEM, FEI Tecnai G20). The elemental composition of the samples were
characterized by energy-dispersive X-ray spectroscopy (EDX, Oxford instruments X-Max).
Surface electronic states were analyzed by X-ray photoelectron spectroscopy (XPS,
Perkin-Elmer PHI 5000C, Al KR). All binding energies were calibrated by using the contaminant
carbon (C1S = 284.6 eV) as a reference. The Fourier transform infrared (FTIR) spectroscopy was
recorded on Nicolet 6700 FTIR Spectrometric Analyzer using KBr pellets.
2.5. Hydrogen generation measurement
The hydrogen generation experiments were performed by a classic water-displacement method.
4
An alkaline-stabilized solution of NaBH (9 mL, 5 wt%) was prepared by the addition of NaOH
(
5 wt%) in a flask for catalytic activity tests. The flask was immersed in thermostatic water bath
to maintain at a given temperature. During the catalytic process, no stirring was adopted due to
5

the presence of vigorous bubble induced by the generated hydrogen, facilitating the contact
between the reactant and the catalyst. For each test, the amount of LSC support was kept the
same (0.01 g) and the total molar amount of (Ag + Co) was kept at a constant of 0.2 mmol.
4
Different experimental parameters such as NaOH concentrations, NaBH concentrations, and
4
temperature were varied for the detailed study on NaBH hydrolysis catalyzed by the LSC/AgCo.
The activation energy was determined by test of hydrogen generation rates at different
temperatures. For recyclability tests, the hydrolysis reactions were repeated four times. The first
4
run refers to the in situ reduction and simultaneous NaBH hydrolysis reaction. For the second to
fourth run, the experiments were carried out in an equivalent volume (9 mL) of 5 wt% NaBH
4
solution containing 5 wt% NaOH.
3. Results and discussion
Loofah sponges are widely used in the kitchen washing in Chinese family, which can be easily
obtained from the fully ripened loofah plant by removal of the skins and seeds. As shown in Fig.
, the natural loofah sponge is consisted of the continuous, flexible, interconnected junction-like
three-dimensional (3D) structure, offering mechanically stable scaffold. Additionally, the
1
-
1
abundant oxygen-containing functional groups, such as hydroxyl group (3429 cm ), C=O bond
-
1
-1
-1
-1
(
1633 cm ), O-C=O bond (1633 cm and 1450 cm ) and O-C-O bond (1503.6 cm ), on the
structure of LSC (Fig. 2), provide the relatively active surface sites for the immobilization of
metallic NPs. Fig. 1 schematically illustrates the fabrication strategy of LSC/AgCo catalysts. The
LSC can be directly obtained by the hydrothermal treatment of the natural loofah sponges. The
+
2+
Ag and Co ions would be easily enriched around the LSC due to the interaction between
negative oxygen-containing groups and metallic cations. The black LSC/AgCo catalysts were
6

4
finally produced by addition of NaBH during chemical reduction process.
The phase structure and crystallinity of the synthesized samples were characterized by X-ray
diffraction (XRD). Fig. 3 shows the typical XRD patterns of the LSC, free Ag0.1Co0.9 and
LSC/Ag0.1Co0.9. The bare LSC shows a broad peak centered at 2θ = 22.6°, corresponding to the
amorphous carbon. For the free Ag0.1Co0.9, three diffraction peaks at 2θ = 38.0°, 44.2° and 64.5°
can be well matched with the standard XRD pattern of metallic Ag (JCPDS file no. 04-0783).
Notably, no detectable peaks assigned to metallic Co was observed in the pattern, indicating the
amorphous nature of Co component. This phenomenon was very similar to the previous
observations for Co-based bimetallic system [13-15]. The relatively high crystallinity of
metallic Ag in bimetallic Ag0.1Co0.9 could be attributed to the higher reduction potentials of
+
0
0
0
2+
0
Ag /Ag (reduction potentials: E Ag+/Ag0 = 0.7996 eV vs. SHE; E Co /Co = 0.28 eV vs. SHE).
+
2+
Thus, Ag can be firstly reduced to metallic Ag prior to Co , which is beneficial for the
subsequent crystal nucleation and growth. In the case of LSC/Ag0.1Co0.9, except the typical
diffraction peaks of Ag0.1Co0.9, a new broad peak corresponding to the LSC located at 2θ =
2
2.6° can be found, confirming the coexistence of Ag0.1Co0.9 and LSC in the product.
The morphologies and microstructures of the LSC, free Ag0.1Co0.9 and LSC/Ag0.1Co0.9 were
observed by scanning electron microscopy (SEM). As shown in Fig. 4a, the individual LSC with
a diameter of 300 µm looks like a tree stump with several shallow channels and small fractures.
The magnified SEM image (Fig. 4b) reveals that the slightly rough surface of the LSC is
wrinkled due to the shrinkage of plant tissues in the loofah sponge during the hydrothermal
treatment process. This unique structure of LSC should be beneficial to the loading of metallic
NPs. Fig. 4c and Fig. 4d show the typical SEM images of free Ag0.1Co0.9, which are composed of
7

spherical particles with size distribution within 50-100 nm. It is clear that these Ag0.1Co0.9 NPs
suffer from serious aggregation due to their high surface energy and magnetic interaction. As
shown in Fig. 4e, the Ag0.1Co0.9 can be grown and stabilized on the LSC support. Unlike the bare
LSC, the surface of the LSC seems to be not smooth, where the fine Ag0.1Co0.9 NPs are anchored
on firmly. Different from free Ag0.1Co0.9 (Fig. 4c), the fine Ag0.1Co0.9 NPs achieve good
dispersion in the presence of the LSC (Fig. 4f), which is critical to heterogeneous catalysis
applications. The microstructure of LSC/Ag0.1Co0.9 was further characterized by transmission
electron microscopy (TEM). As shown in Fig. S1a, the Ag0.1Co0.9 NPs are well-loaded on the
LSC matrix. No free NPs are found outside of the LSC support during the TEM observation,
indicating a perfect combination between the LSC and Ag0.1Co0.9 NPs. The high-magnified TEM
image (Fig. S1b, Supporting Information) further shows that the crystalline Ag (dark region) is
fully surrounded by the amorphous Co (grey region), suggesting that Ag is initially reduced by
4
NaBH , and acts as the center helping for the subsequent growth of Co. Such structure of Ag
surrounded by Co is consistent with the previous observations on bimetallic AgCo systems [15,
3, 24]. Moreover, the d-spacing of the crystallized dark region (inset in Fig. S1b, Supporting
2
Information) is 0.236 nm, corresponding to the Ag(111) plane spacing.
The elemental composition and electronic structure of the LSC/Ag0.1Co0.9 were determined by
X-ray photoelectron spectroscopy (XPS). Fig. 5a shows high-resolution XPS spectrum of the
C1s. Three surface components in the spectrum at approximately 284.8 eV (C-C or C-H), 286.3
eV (C-OH or C-O) and 289.0 eV (O-C=O) [25, 26]. The high-resolution XPS spectrum of the O
1s (Fig. 5b) is fitted by four chemical states at binding energies of 531.2, 532.1, 535.9 and 530.6
eV, which can be ascribed to O in the form of C=O, C-O, B-O, O-H from adsorbed water [25, 26]
8

and Co-O bond due to oxidation of metallic Co [27], respectively. As shown in Fig. 5c, the
binding energies at 778.5 and 781.2 eV correspond to metallic Co(0) and surface Co(II) species
due to the partial surface oxidization, respectively. The shakeup satellite peak (786.2 eV) at
approximately 5 eV above the main peak is further evidence of surface Co(II) species. The
detectable Co(II) species can be ascribed to the surface Co combined with oxygen of atmosphere
during the catalyst preparation and storage process, which is similar to the other cobalt-based
catalysts [13-15]. The Ag 3d core level spectrum (Fig. 5d) shows two distinct peaks at 367.7 and
373.7 eV, which could be attributed to Ag 3d5/2 and Ag 3d3/2 of metallic Ag, respectively.
Meanwhile, the 6.0 eV difference between the binding energies of Ag 3d5/2 and Ag 3d3/2 is also
characteristic of the metallic Ag 3d states [28], confirming the presence of air-stable metallic Ag
-
in the LSC/AgCo product. Of note, a prominent peak at around 192 eV assigned to B-O in BO
2
species appears in the high-resolution XPS spectrum of the B 1s (Fig. S2, Supporting
2
Information), suggesting that a certain amount of NaBO by-product may be deposited on the
sample surface during preparation process [29]. In addition, the energy-dispersive X-ray
spectrometry (EDX) also confirms these elements coexisted in the LSC/Ag0.1Co0.9 (Fig. S3,
Supporting Information). The composition of Ag:Co ratio in the LSC/Ag0.1Co0.9 is found to be
approximately 89.75:10.25, which is very close to its feeding ratio.
4
The catalytic activities of LSC/AgCo were evaluated by the hydrolysis of NaBH for hydrogen
4
generation. Fig. 6 shows the amounts of generated hydrogen from NaBH aqueous solution as a
function of reaction time by using various catalytic systems. The LSC as a catalyst is incapable
4
of catalyzing the hydrolysis of NaBH , evidenced by the negligible hydrogen generation. In
contrast, the considerable hydrogen generation occurred under same reaction condition in the
9

presence of free AgCo NPs (Ag0.1Co0.9), indicating the AgCo NPs are active in the catalytic
4
hydrolysis of NaBH . Interestingly, after combination with the LSC support, the obtained
4
LSC/Ag0.1Co0.9 exhibits more remarkable catalytic activity toward NaBH hydrolysis than that of
-
1
free Ag0.1Co0.9, where the corresponding reaction rate constant increases from 65.84 mL·min to
-
1
8
2.01 mL·min . We therby deduce that the catalytic ability should be originated from the existed
Ag0.1Co0.9 component, whereas enhanced efficiency could be attributed to the cooperation
between LSC and Ag0.1Co0.9. Furthermore, the LSC/AgCo presents the composition-dependent
catalytic activity, as shown in Fig. 7a. No detectable hydrogen generation is observed for
LSC/Ag, while the moderate amounts of hydrogen generation was produced by LSC/Co.
Interestingly, the bimetallic LSC/AgCo exhibits much higher catalytic activity than that of
monometallic LSC/Ag and LSC/Co, appearing the accelerated hydrogen generation performance.
However, the activity differences among them could be still clearly distinguished. The rationally
controlled Ag content in LSC/AgCo is critical to the optimized catalytic activity. The apparent
-1
reaction rate constants were calculated to be 82.01, 58.92, 37.2 and 38.99 mL·min for
LSC/Ag0.1Co0.9, LSC/Ag0.2Co0.8, LSC/Ag0.3Co0.7, and LSC/Ag0.5Co0.5, respectively. The
4
LSC/Ag0.1Co0.9 achieves the best catalytic activity toward the hydrolysis of NaBH among all of
the samples. The qualitative analysis further reveals that LSC/Ag0.1Co0.9 possesses a catalytic
activity of 3.07 times that of Ag-absent LSC/Co (Fig. 7b). Considering the poor catalytic
performance of individual components, a synergetic interaction between Ag and Co in
LSC/AgCo plays a critical role in catalytic reaction. As widely accepted, bimetallic system is a
well-known phenomenon that can remarkably improve the catalytic activity of the original
monometal catalysts for different chemical processes [30-32]. In our case, the excellent catalytic
1
0

activity of LSC/Ag0.1Co0.9 is attributed to the combination of strain and ligand effects caused by
the atomic environment of distinct metal atoms on bimetallic surfaces, which could by promoted
by the surface plasmon resonance (SPR) effect of metallic Ag NPs [33]. The SPR-induced
oscillating electric fields would deepen the d-band center position of the neighbouring Co atoms,
leading to their low adsorption energy and high reactivity [34]. Based on these considerations, it
is reasonable to believe that the supporting effect of LSC and intermetallic electronic interactions
between Ag and Co in LSC/AgCo catalysts could cooperate together to catalyze NaBH
4
hydrolysis to significantly promote the hydrogen generation.
Fig. 8 shows the effect of variation in NaOH concentrations on hydrogen generation
performance over LSC/Ag0.1Co0.9. Although the addition of NaOH could efficiently inhibit the
4
self-hydrolysis of NaBH , the catalytic activity of LSC/Ag0.1Co0.9 is still closely dependent on
the NaOH concentration. For example, when the NaOH concentrations were increased in the
range of 1-5 wt%, the hydrogen generation rates were accelerated markedly from 43.44 to 82.01
-1
mL·min . However, further increasing the NaOH concentrations up to 10 wt% leads to
significantly lowering the rate of hydrogen generation. This phenomenon is very similar to the
previous observations reported in other catalytic systems [35-37]. In terms of these results, it is
4
expected that NaOH plays multiple role for the catalytic hydrolysis of NaBH . An appropriate
4
amount of NaOH is critical to the catalytic activity, ensuring stability of NaBH in aqueous
solution, while the excess amounts of added NaOH increase the alkalinity and viscosity of the
solution, retarding the mass transfer rate in catalytic systems.
4
Fig. 9 shows the effect of NaBH concentrations on the catalytic activity of LSC/Ag0.1Co0.9.
As a hydrogen source in the hydrolysis reaction, kinetics of the catalytic reaction should be
11

4
associated with NaBH concentration. It is clear that hydrogen generation rate increases
4
remarkably with increasing NaBH concentration from 1 wt% to 5 wt%, and then keeps almost a
4
constant when further increasing NaBH concentration to 10 wt%. However, hydrogen
4
generation rate was found to decline as the NaBH concentration reaches up to 15 wt%. This is
4
mainly ascribed to following two aspects: (1) increasing NaBH concentration results in the
increased viscosity of reaction medium, slowing down the mass transfer rate; (2) the self-formed
2
NaBO with relatively lower solubility could destroy active sites on the catalyst surface and
4
interrupt contact between catalyst and NaBH . Thereby, these results clearly indicate that in order
to achieve high hydrogen generation rates, both NaBH
appropriate concentrations.
4
and NaOH should be controlled in the
4
Fig. 10a shows the catalytic activity of LSC/Ag0.1Co0.9 toward the hydrolysis of NaBH at
different temperatures. It can be clearly seen that this catalytic reaction is very sensitive to this
parameter. More specifically, when the temperature was increased from 20 to 50 °C, the rates of
-1
hydrogen generation increased rapidly from 32.41 to 208.73 mL·min , indicating the
temperature-promoted catalytic activity. Furthermore, according to the values of the rate constant
(
k) calculated from the slope of the linear part of each plot in Fig. 10a, the activation energy (E
a
)
of catalytic reaction can be determined. Fig. 10b shows the Arrhenius plot of ln k vs. the
-
1
reciprocal absolute temperature (1/T). The E
a
is estimated to be about 49.27 kJ·mol , which is
lower than the reported values for the NaBH
4
hydrolysis catalyzed by hydroxyapatite-supported
-1
-1
-1
Co nanoclusters (50 kJ mol ) [38], Co/IR-120 (66.67 kJ mol ) [39], Ru/MMT (54.5 kJ mol )
-
1
[
40], carbon-supported Co-B (56.72 kJ mol ) [41], attapulgite clay-supported Co-B (56.32 kJ
-1
-1
-1
mol ) [42], Co-Cu-B (49.6 kJ mol ) [43], Co-La-Zr-B (53 kJ mol ) [44], Ni-Ru/50WX8 (52.73
1
2

-1
-1
-1
kJ mol ) [45], graphite supported Ru (61.10 kJ mol ) [46], and Ru/C (52.12 kJ mol ) [47].
Considering that the catalyst’s durability is critical to the practical application, we performed
recycling experiments to evaluate the reusability of the LSC/Ag0.1Co0.9 catalyst. After catalytic
reaction, the LSC/Ag0.1Co0.9 catalyst can be effectively separated by using an external magnet,
due to its sensitively magnetic response (Fig. 1). By combination of the magnetic recyclability,
the catalytic activity test was repeated four times, and the results are shown in Fig. 11. It is found
that the catalytic activity of the LSC/Ag0.1Co0.9 decreases continuously with increasing the
cycling time. Similar observations were reported in other bimetallic catalytic systems [14, 48,
49]. The decrease of recycle stability could be attributed to the increased viscosity of the solution
and deactivation effect of the increasing metaborate concentration during the hydrolysis process.
4. Conclusions
In summary, we demonstrate that the hydrothermal-derived loofah sponge carbon can be
served as an effective solid support for loading bimetallic nanoparticles. The as-fabricated
4
LSC/AgCo exhibited superior performance for the catalytic hydrolysis of NaBH towards
hydrogen generation. The LSC can stabilize the AgCo NPs to promote the hydrogen generation
efficiency during the catalytic hydrolysis process. The LSC/AgCo catalysts also show the
composition-dependent catalytic activity, with LSC/Ag0.1Co0.9 being the most active. The
catalytic hydrolysis process was found to be affected by other factors, such as substrate
concentration and reaction temperature. The activation energy for catalytic hydrolysis reaction is
-1
4
9.27 kJ·mol . The as-prepared LSC/AgCo catalysts with high hydrogen generation efficiency
and low activation energy provides an effective pathway for the economical and sustainable
implementation of biomass for the chemical hydrogen storage.
1
3

Acknowledgements
This work was supported by the National Natural Science Foundation of China (21103141 and
21207108), the Sichuan Youth Science and Technology Foundation (2013JQ0012), and the
Research Foundation of CWNU (12B018).
Appendix A. Supporting information
Supplementary data associated with this article can be found in the online version at
http://dx.doi.org/10.1016/j.jallcom. xxxxxxxx.
References
[
1] S. Zinoviev, F. Muller-Langer, P. Das, N. Bertero, P. Fornasiero, M. Kaltschmitt, G. Centi, S.
Miertus, ChemSusChem 3 (2010) 1106-1133.
2] M. Li, D.A. Cullen, K. Sasaki, N.S. Marinkovic, K. More, R.R. Adzic, J. Am. Chem. Soc.
35 (2013) 132-141.
[
1
[
[
[
3] L. Chong, J. Zou, X. Zeng, W. Ding, J. Mater. Chem. A 1 (2013) 3983-3991.
4] M. Yadav, Q. Xu, Energy Environ. Sci. 5 (2012) 9698-9725.
5] Z. Sun, J. Masa, W. Xia, D. Konig, A. Ludwig, Z.-A. Li, M. Farle, W. Schuhmann, M.
Muhler, ACS Catal. 2 (2012) 1647-1653.
6] M. Heggen, M. Oezaslan, L. Houben, P. Strasser, J. Phys. Chem. C 116 (2012)
9073-19083.
[
1
[
(
[
[
7] H. Yin, S. Liu, C. Zhang, J. Bao, Y. Zheng, M. Han, Z. Dai, ACS Appl. Mater. Interfaces 6
2014) 2086-2094.
8] D. Sun, V. Mazumder, O. Metin, S. Sun, ACS Catal. 2 (2012) 1290-1295.
9] D. Sun, V. Mazumder, O. Metin, S. Sun, ACS Nano 5 (2011) 6458-6464.
1
4

[
10] J.-M. Yan, X.-B. Zhang, T. Akita, M. Haruta, Q. Xu, J. Am. Chem. Soc. 132 (2010)
326-5327.
5
[
[
[
[
(
[
[
[
11] H.-L. Jiang, T. Akita, Q. Xu, Chem. Commun. 47 (2011) 10999-11001.
12] N. Cao, J. Su, W. Luo, G. Cheng, Int. J. Hydrogen Energy 39 (2014) 426-435.
13] L. Yang, J. Su, W. Luo, G. Cheng, Int. J. Hydrogen Energy 39 (2014) 3360-3370.
14] W. Feng, L. Yang, N. Cao, C. Du, H. Dai, W. Luo, G. Cheng, Int. J. Hydrogen Energy 39
2014) 3371-3380.
15] L. Yang, J. Su, X. Meng, W. Luo, G. Cheng, J. Mater. Chem. A 1 (2013) 10016-10023.
16] X. Gu, Z.-H. Lu, H.-L. Jiang, T. Akita, Q. Xu, J. Am. Chem. Soc. 133 (2011) 11822-11825.
17] H.-L. Jiang, T. Akita, T. Ishida, M. Haruta, Q. Xu, J. Am. Chem. Soc. 133 (2011)
1304-1306.
[
[
[
[
[
[
[
[
[
18] J. Li, Q.-L. Zhu, Q. Xu, Chem. Commun. 50 (2014) 5899-5901.
19] P.-Z. Li, K. Aranishi, Q. Xu, Chem. Commun. 48 (2012) 3173-3175.
20] L. Ai, H. Yue, J. Jiang, J. Mater. Chem. 22 (2012) 23447-23453.
21] L. Ai, J. Jiang, Bioresour. Technol. 132 (2013) 374-377.
22] L. Ai, X. Gao, J. Jiang, J. Power Sources 257 (2014) 213-220.
23] N.S. Sobal, M. Hilgendorff, H. Mohwald, M. Giersig, Nano Lett. 2 (2002) 621-624.
24] L. Yang, W. Luo, G. Cheng, ACS Appl. Mater. Interfaces 5 (2013) 8231-8240.
25] P. Nowicki, R. Pietrzak, H. Wachowska, Energy Fuels 24 (2010) 1197-1206.
26] V.O.A. Tanobe, T.H.D. Sydenstricker, M. Munaro, S.C. Amico, Polym. Testing 24 (2005)
474-482.
[
27] Q. Jiao, M. Fu, C. You, Y. Zhao, H. Li, Inorg. Chem. 51 (2012) 11513-11520.
1
5

[
[
[
[
[
28] M. Pang, J. Hu, H.C. Zeng, J. Am. Chem. Soc. 132 (2010) 10771-10785.
29] G.M. Arzac, T.C. Rojas, A. Fernández, Appl. Catal. B 128 (2012) 39-47.
30] T.A. Maark, A.A. Peterson, J. Phys. Chem. C 118 (2014) 4275-4281.
31] A.E. Baber, H.L. Tierney, E.C.H. Sykes, ACS Nano 4 (2010) 1637-1645.
32] J.B. Henry, A. Maljusch, M. Huang, W. Schuhmann, A.S. Bondarenko, ACS Catal. 2 (2012)
1457-1460.
[
[
[
[
[
[
[
33] B. Zhou, M. Wen, Q. Wu, Nanoscale 5 (2013) 8602-8608.
34] J. Gu, Y.W. Zhang, F. Tao, Chem. Soc. Rev. 41 (2012) 8050-8065.
35] F. Li, Q. Li, H. Kim, Chem. Eng. J. 210 (2012) 316-324.
36] M. Zahmakiran, S. Ozkar, Langmuir 25 (2009) 2667-2678.
37] N. Sahiner, O. Ozay, E. Inger, N. Aktas, Appl. Catal. B: Environ. 102 (2011) 201-206.
38] M. Rakap, S. Özkar, Catal. Today 183 (2012) 17-25.
39] C.-H. Liu, B.-H. Chen, C.-L. Hsueh, J.-R. Ku, F. Tsau, K.-J. Hwang, Appl. Catal. B:
Environ. 91 (2009) 368-379.
[
[
[
[
[
[
40] S. Peng, X. Fan, J. Zhang, F. Wang, Appl. Catal. B: Environ. 140-141 (2013) 115-124.
41] F. Baydaroglu, E. Ozdemir, A. Hasimoglu, Int. J. Hydrogen Energy 39 (2014) 1516-1522.
42] H. Tian, Q. Guo, D. Xu, J. Power Sources 195 (2010) 2136-2142.
43] X.-L. Ding, X. Yuan, C. Jia, Z.-F. Ma, Int. J. Hydrogen Energy 35 (2010) 11077-11084.
44] M.H. Loghmani, A.F. Shojaei, Int. J. Hydrogen Energy 38 (2013) 10470-10478.
45] C.-H. Liu, B.-H. Chen, C.-L. Hsueh, J.-R. Ku, M.-S. Jeng, F. Tsau, Int. J. Hydrogen Energy
34 (2009) 2153-2163.
[
46] Y. Liang, H.-B. Dai, L.-P. Ma, P. Wang, H.-M. Chen, Int. J. Hydrogen Energy 35 (2010)
1
6

3
023-3028.
47] Y.C. Zou, M. Nie, Y.M. Huang, J.Q. Wang, H.L. Liu, Int. J. Hydrogen Energy 36 (2011)
2343-12351.
48] D.-R. Kim, K.-W. Cho, Y.-I. Choi, C.-J. Park, Int. J. Hydrogen Energy 34 (2009)
622-2630.
49] C. Du, J. Su, W. Luo, G. Cheng, J. Mol. Catal. A 383-384 (2014) 38-45.
[
1
[
2
[
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Figure captions
Fig. 1. Schematic illustration for the synthesis procedure of LSC/AgCo catalyst
Fig. 2. FTIR spectrum of the LSC
Fig. 3. XRD patterns of the LSC, free Ag0.1Co0.9 and LSC/Ag0.1Co0.9
Fig. 4. SEM images of the LSC (a,b), free Ag0.1Co0.9 (c,d) and LSC/Ag0.1Co0.9 (e,f)
Fig. 5. XPS spectra of the LSC/Ag0.1Co0.9: (a) C 1s, (b) O 1s, (c) Co 2p and (d) Ag 3d
4
Fig. 6. Hydrogen generation from NaBH aqueous solution (5 wt%) catalyzed by LSC, free
Ag0.1Co0.9 and LSC/Ag0.1Co0.9 at 30 °C
4
Fig. 7. (a) Hydrogen generation from NaBH aqueous solution (5 wt%) catalyzed by
x
LSC/Ag Co1-x (x = 0, 0.1, 0.2, 0.3, 0.5, and 1) at 30 °C. (b) Activity enhancement factor
x
(kLSC/AgCo/kLSC/Co) and the corresponding apparent reaction rate k(inset) of LSC/Ag Co1-x
Fig. 8. Catalytic activity of the LSC/Ag0.1Co0.9toward the hydrogen generation by hydrolysis of
4
NaBH solution (5 wt%) containing different concentrations of NaOH at 30 °C
Fig. 9. Catalytic activity of the LSC/Ag0.1Co0.9 toward the hydrogen generation byhydrolysis of
4
different concentrations of NaBH solution containing 5 wt% NaOH at 30 °C
Fig. 10. (a) Catalytic activity of the LSC/Ag0.1Co0.9 toward the hydrogen generation by
4
hydrolysis of NaBH solution (5 wt%) containing 5 wt% NaOH at different temperatures. (b)
Arrhenius plot of ln k vs. the reciprocal absolute temperature (1/T)
4
Fig. 11. Reusability test of hydrogen generation from hydrolysis of NaBH solution (5 wt%)
containing 5 wt% NaOH catalyzed by the LSC/Ag0.1Co0.9 at 30 °C
1
8

Fig. 1.
1
9

Fig. 2.
2
0

Fig. 3.
2
1

Fig. 4.
2
2

Fig. 5.
2
3

Fig. 6.
2
4

Fig. 7.
2
5

Fig. 8.
2
6

Fig. 9.
2
7

Fig. 10.
2
8

Fig. 11.
2
9