Highly active and durable catalyst for hydrogen generation by the NaBH4 hydrolysis reaction: CoWB/NF nanodendrite with an acicular array structure

Article abstract of DOI:10.1016/j.jallcom.2020.155429

Sodium borohydride (NaBH₄) hydrolysis is a promising technology to produce high-purity hydrogen (H₂) on-site for fuel cells. However, the widespread applications of this technology are hampered by the low catalytic activity and poor stability of the catalyst for hydrogen production. To develop a low-cost catalyst with high activity and good stability, a novel CoWB catalyst supported by nickel foam was prepared by the pulse electrodeposition method for H₂ production from a NaBH₄ alkaline solution. The SEM results revealed that in the special microstructure of nanodendrites with acicular arrays, CoWB was uniformly plated on the surface of the Ni foam (NF) substrate and firmly adhered to the surface. The tungsten doping decreased the activation energy to as low as 18.15 kJ mol^?1. The CoWB/NF catalyst exhibited higher hydrogen producing performance, and the hydrogen generation rate (HGR) reached 14.13 L min^?1·g^?1 cat, which was comparable to that of the noble metal catalyst. More importantly, the catalyst demonstrated very good stability, as the catalytic activity was maintained at 82% of its initial activity after 800 h of usage. The CoWB/NF catalyst of the hydrogen generator contributed to the generation of hydrogen with 99.9871% purity at an HGR of 1.07 L/min. This study demonstrated that the novel CoWB/NF catalyst is very promising for hydrogen production from the NaBH₄ hydrolysis reaction.

Full text of DOI:10.1016/j.jallcom.2020.155429

Journal of Alloys and Compounds 836 (2020) 155429
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Highly active and durable catalyst for hydrogen generation by the
NaBH hydrolysis reaction: CoWB/NF nanodendrite with an acicular
4
array structure
Yongsheng Wei a
,
b
,
*
, Maosen Wang , Wenying Fu , Lu Wei , Xinsheng Zhao ,
a
a
a
a
b
c
,
**
d, ***
Xiangyang Zhou , Meng Ni
, Haijiang Wang
a
School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou, 221116, PR China
b
c
Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL, 33124, USA
Department of Building and Real Estate, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen, 518055, PR China
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 November 2019
Received in revised form
Sodium borohydride (NaBH ) hydrolysis is a promising technology to produce high-purity hydrogen (H )
4
2
on-site for fuel cells. However, the widespread applications of this technology are hampered by the low
catalytic activity and poor stability of the catalyst for hydrogen production. To develop a low-cost catalyst
with high activity and good stability, a novel CoWB catalyst supported by nickel foam was prepared by
the pulse electrodeposition method for H production from a NaBH alkaline solution. The SEM results
2 4
revealed that in the special microstructure of nanodendrites with acicular arrays, CoWB was uniformly
20 April 2020
Accepted 28 April 2020
Available online 8 May 2020
plated on the surface of the Ni foam (NF) substrate and firmly adhered to the surface. The tungsten
Keywords:
ꢀ
1
doping decreased the activation energy to as low as 18.15 kJ mol . The CoWB/NF catalyst exhibited
higher hydrogen producing performance, and the hydrogen generation rate (HGR) reached
Sodium borohydride
Hydrogen generation rate
CoWB/NF Nanodendrite
Service life
ꢀ
1
ꢀ1
14.13 L min $g cat, which was comparable to that of the noble metal catalyst. More importantly, the
catalyst demonstrated very good stability, as the catalytic activity was maintained at 82% of its initial
activity after 800 h of usage. The CoWB/NF catalyst of the hydrogen generator contributed to the gen-
eration of hydrogen with 99.9871% purity at an HGR of 1.07 L/min. This study demonstrated that the
Pulse electrodeposition
novel CoWB/NF catalyst is very promising for hydrogen production from the NaBH
4
hydrolysis reaction.
©
2020 Elsevier B.V. All rights reserved.
1. Introduction
lack of efficient and low-cost hydrogen production and storage is
still a major challenge towards the commercialization of fuel cell
Hydrogen is an attractive energy carrier due to its high abun-
dance, high energy density and environmentally friendly utilization
4
power systems. Sodium borohydride (NaBH ), as a typical example
of chemical hydrides, has been considered a safe and convenient
hydrogen source due to its high hydrogen storage capacity (10.8 wt
%), nontoxicity, ambient operation temperature, and hydrolysis
reaction controllability [2e4].
However, the wide application of NaBH is impeded by the high
4
cost (the use of noble metal catalysts) and relatively poor stability of
the catalyst. The development of a low-cost, durable and active
[
1]. Hydrogen can be used in lightweight proton exchange mem-
brane fuel cells (PEMFCs) for power generation with a high energy
efficiency, releasing only water and heat. Therefore, PEMFCs fueled
with pure hydrogen have been considered one of the most prom-
ising power sources for portable applications such as hydrogen fuel
cell vehicles and unmanned aerial vehicles (UAVs). However, the
catalyst for the NaBH
on-site hydrogen production for fuel cell applications. Hydrolysis of
NaBH is activated by various catalysts, including platinum, rhodium,
ruthenium [5], cobalt, and nickel. Platinum [6e8], rhodium, and
ruthenium [7e16] are effective catalysts, but these catalysts are very
expensive, hindering large-scale commercial applications. Cobalt-
based [17e39] and nickel-based [29e31,40e42] catalysts show
4
hydrolysis reaction is thus the key to efficient
*
Corresponding author. School of Physics and electronic engineering, Jiangsu
4
Normal University, Xuzhou, 221116, PR China.
*
*
* Corresponding author.
** Corresponding author.
E-mail addresses: weiys@jsnu.edu.cn (Y. Wei), meng.ni@polyu.edu.hk (M. Ni),
wanghj@sustech.edu.cn (H. Wang).
https://doi.org/10.1016/j.jallcom.2020.155429
0925-8388/© 2020 Elsevier B.V. All rights reserved.

2
Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
good catalytic activities and hydrogen production rates for the hy-
drolysis of NaBH . The main reason is that the metal Co has an
amorphous structure, and it is characterized by short-range ordering
and long-distance disorder, a high concentration of unsaturated sites
and good chemical stability. CoeB alloy- and CoeB-based catalysts
given in our previous publications [52e54], as shown in Fig. 1.
Essentially, NF (Ni foam, 1 cm ꢁ 1 cm) was first immersed in
4
ꢂ
ethanol and ultrasonicated at 25 C for 30 min to remove the greasy
dirt on the surface, followed by soaking in 10 vol% HCl solution for
15 min at room temperature to remove inorganic impurities.
Finally, all the samples were cleaned by deionized water.
4
are also considered good candidates for NaBH hydrolysis owing to
their satisfactory activity and low cost [24,43e46]. The addition of
element B can produce a synergistic effect between metal Co and B
and show better catalytic activity. However, nonnoble metal cata-
lysts are usually less efficient than noble metal catalysts, and they
may also suffer from poor stability for hydrogen production. Liang Y
et al. prepared an FeeCoeB/Ni catalyst, whose catalytic performance
decreased to 54% after 6 cycles [47]. The catalytic performance of the
CoeB catalyst synthesized by Komova et al. [48] was reduced to 40%
after 14 reaction cycles. Kim et al. [29] reported that the catalytic
performance of CoeNieP decreased to 25% after 15 cycles. The cat-
alytic performance of the NieRu catalyst synthesized by AMFR et al.
In a typical run, the pretreated NF was impregnated in the CoCl
EG solution for 3 h and then plated in a mixed 50 C solution
2
ꢂ
2 3 4
including Na WO , NaBH , and NaOH. The pulse electrodeposition
2
current density was 200 mA/cm at a Ton time of 2 ms, a Toff time of
5 ms, and a total plate time of 900 s. The catalysts were thoroughly
washed with ethanol and deionized water and were finally dried in
a vacuum oven at 323 K for 12 h. The prepared catalyst was denoted
as CoWB/NF.
2
.3. Characterization
[
49] decreased to 25% after 300 cycles. Recently, it was found that the
CoWB catalyst is highly effective for catalyzing hydrogen generation
from a NaBH alkaline solution [24,50,51]. However, CoWB also
The composition of the CoWB/NF catalyst was determined by
conventional X-ray powder diffraction (XRD) on a Rigaku D/MAX-
RB diffractometer (Rigaku, Japan). The surface morphology of the
catalyst was studied by scanning electron microscopy (SEM,
HITACHI S-4300, Japan) equipped with energy-dispersive spec-
troscopy analysis (EDS). X-ray photoelectron spectroscopy (XPS,
Thermo ESCALAB 250) measurements were conducted to deter-
mine the chemical bonding states. Specific surface areas were
determined by a BrunauerꢀEmmettꢀTeller (BET) surface area
analyzer (Autosorb-IQ).
4
suffers from an agglomeration phenomenon that limits its durability.
It is expected that the catalyst activity and durability can be
enhanced by loading the catalyst on high-surface-area supporting
materials or by doping suitable elements into the catalyst. Most
catalyst supports are porous materials, including NF (nickel-form),
2 3
carbon spheres, g-Al O , honeycomb ceramics, etc. Among them, NF,
having a porous structure, low areal density, and high thermal and
chemical stability under hydrolysis conditions, is considered one of
the best supports for catalysts. In this work, a novel CoWB catalyst
supported by nickel foam was fabricated by a pulse electrodeposition
2
.4. Hydrogen generation rate (HGR) test
(
PED) method. The CoWB/NF catalyst synthesized using the method
exhibited a high activity and durability towards the hydrolysis re-
action in NaBH solution.
The HGR was measured by a classical water-displacement
method. Typically, the HGR was tested in a 100 mL three-neck
4
flask immersed in a constant temperature bath. First, 10 g of an
2
. Experimental
aqueous solution consisting of NaBH (5 wt%) and NaOH (2 wt%) was
4
added into the flask, and then the CoWB/NF catalyst was rapidly
2
.1. Chemicals
added to initiate the hydrolysis reaction under stirring. The volume
of the evolved hydrogen was recorded by the volume of drained
water of the bird-shaped bottle. Each measurement was repeated 3
NF was purchased from Hunan Liyuan New Martials Company.
Cobalt chloride hexahydrate (CoCl.
6H
, AR), sodium borohydride (NaBH
NaOH, AR) and ethylene glycol (EG, AR) were obtained from
O, AR), sodium tungsten
ꢀ1
ꢀ1
2
2
times. The average HGR was normalized as mL$min $g (CoWB).
(
(
Na
2
WO
3
4
, AR), sodium hydroxide
V
HGR ¼
(1)
Sinopharm Chemical Reagent Co., Ltd. Alcohol and hydrochloric
acid were purchased from Beijing Chemicals Ltd. Deionized water
was used as the solvent whenever water was used in the synthesis
and experiments.
t*ðm
2
ꢀ m
1
Þ
where m is the weight of dried catalyst before PED, m
1
2
is the
weight of dried catalyst after PED, t is the time of hydrogen pro-
duction, and V is the generated volume of hydrogen.
2.2. Preparation
2.5. Solution uptake test
Nanodendritic-structured CoWB/NF catalysts were prepared by
pulse electrodeposition (PED). The methods were similar to those
The solution uptake (SU) in the catalyst was determined and
calculated through the difference value between the mass before
and after the catalyst was immersed into the NaBH alkaline solu-
4
tion. Catalyst samples were weighed three times on an electronic
balance after drying in a vacuum drying oven for 300 min at 323 K,
and the average mass was denoted as m
put into different concentrations of a NaBH
NaOH) for 10 min and then removed. The catalyst samples were
weighed three times again, and the average mass was denoted as
3
. The catalyst sample was
4
alkaline solution (2 wt
%
m
4
. The solution uptake (SU) value was calculated by formula (2).
m ꢀ m
4
3*100%
SU ¼
(2)
m
3
Fig. 1. Schematic illustration of the CoWB/NF nanodendrite catalyst by pulse
electrodeposition.

Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
3
2
.6. Durability of catalyst
branches that from the site, providing more accessible active sites
for the reactants [55]. The AFM images shown in Fig. 2(j) display the
nanostructure of the acicular array in the extremity of the side
Catalyst samples were dipped into different concentrations of
2
NaBH
4
alkaline solution (2 wt% NaOH) for 16 h every time and then
branch. There are 167 peaks in the 25 nm area. The average dis-
removed and washed with 1 M HCl to remove the surface residual
liquid [54]. The HGR was tested at the beginning every time. This
process was repeated fifty times, and the durability results were
obtained by data processing.
tance between peaks is 0.31 nm. This further proves that the den-
dritic structure has abundant branch tips as catalytic active sites.
Fig. 2 (b) shows energy dispersive spectra corresponding to the
selected zone in the CoWB catalyst indicated in the inset. The EDS
analysis shows that the catalyst coating consisted of the three el-
ements studied, namely, Co, B and W, and their atomic ratio is
3
. Results and discussion
5
1:19:3. In addition, the C signal in the spectra can be attributed to
the conductive adhesive introduced during sample preparation. In
addition, the O signal might come from the adsorbed oxygen or H
50].
Fig. 2 (d) shows the X-ray diffraction (XRD) patterns of the
3.1. Catalyst characterization
2
O
[
The surface morphologies of the NF and CoWB/NF catalysts are
shown in Fig. 2(a). Compared to the smooth surface of the NF, a
large-area forest-like catalyst coating was observed on NF with a
nanodendritic structure formed in the pulse electrodeposition
process. The enlarged photographs in Fig. 2 (c) clearly show that
CoWB grew with a nanosized dendritic structure. The TEM image
shown in Fig. 2(e) further exhibits its nanodendritic structure. The
main reason is that the CoWB/NF catalyst has a highly preferred
orientation in the growth process by PED. This special structure
could provide favorable sites not only for the CoWB catalyst to be
firmly rooted in NF but also for the growth of abundant side
CoWB/NF catalyst. The catalyst sample CoWB/NF was typical of a
crystalline-phase structure with sharp crystalline Ni peaks at 2
ꢂ
ꢂ
ꢂ
theta values of 45 , 52 and 76 . After pulse deposition, the as-
synthesized CoWB/NF evolved from the crystalline phase to an
amorphous structure in the PED process [56].
As shown in Fig. 2(fei), the surface species and electronic
structures of the CoWB/NF catalyst were studied by X-ray photo-
electron spectroscopy (XPS). The XPS results clearly show the peaks
belonging to Co, W, B and Ni in the CoWB/NF NDs. The atomic ratio
Fig. 2. General characterization of the CoWB/NF catalyst. (a, c) SEM morphologies of CoWB/NF. (b) EDS of CoWB/NF. (d) XRD of CoWB/NF. (e) TEM image of CoWB/NF. (fei) XPS
survey of the CoWB/NF catalyst. (j) AFM image of CoWB/NF.

4
Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
ꢀ
ꢂ
of Co, B, and W is 51:17:1, which is similar to the EDS measurement
results. In the deconvoluted XPS spectrum of Co 2p (Fig. 2(f)), two
peaks located at 780.73 and 796.68 eV are assigned to the binding
energies of Co 2p3 and Co 2p1, which indicates the presence of
metallic Co close to the electrode surface. Additionally, the peak
centered at 780.9 eV is attributed to the main peak of oxidized Co
solution can yield H
HGR of the CoWB/NF catalyst increased with increasing reaction
2
at an HGR of 1.711 L min 1$gꢀ1 at 30 C. The
ꢀ
1
ꢀ1
temperature, and the HGR reached as high as 14.13 L min $g
(CoWB) at 70 C. Due to the doped W, the d-band character of W
dominates the band structure of the catalyst surface and then af-
ꢂ
4
fects the electrocatalytic activity of the NaBH hydrolysis reaction
2
p3. Fig. 2(g) shows the W 4f spectrum, with the binding energy
[24,50,51]. The activation energy was calculated using the Arrhe-
nius equation. The regression coefficients and activation energy at
different W/Co ratios are given in Table 1 and Fig. 3(b and c). The
located at 34.73 eV assigned to W 4f5, which exhibits a clear shift to
a lower value (33.5 eV for standard W 4f5). As is well known, the d-
band character of W dominates the band structure of the catalyst
ꢀ1
activation energy of CoWB/NF has a lower value of 18.15 kJ mol at
surface and then affects the electrocatalytic activity of the NaBH
4
a 40% W/Co ratio, resulting in an easier reaction path for NaBH
hydrolysis.
4
hydrolysis reaction. Fig. 2(h) shows the B 1s spectrum, with the
peak located at 191.68 eV assigned to WB and the peak at 194.4 eV
assigned to B oxide caused by the oxidation of the catalyst surface.
Modification of the electronic structure occurs after the PED pro-
cess, resulting in an upshift of the d-band center for the CoWB/NF
NDs that may alter the chemisorption of reactants, intermediates,
and products and thus enhance the electrochemical performance in
the hydrogen generation reaction.
3.3. Solution uptake
It is necessary to consider the solution uptake in the porous
catalyst for the hydrolysis of sodium borohydride. The porous
structure provides a reaction pathway and space for gas-liquid two-
phase flow of hydrogen gas and NaBH . At the same time, the
4
Fig. 4 shows that the BET surface area of the CoWB/NF catalyst is
5.56 m /g, which is larger than that of the CoB/NF catalyst. The
main reason is the W doping and nanodendrites with acicular array
structures growing on the Ni foam surface by pulse electrodepo-
sition. This larger surface area provides more active sites for the
hydrolysis of sodium borohydride.
porous catalyst can partially maintain a mixed reaction solution. It
2
3
will take time to stop hydrogen gas production on the surface of the
catalyst when the catalyst is removed from the solution. The
trailing time affects the control of the hydrogen-producing system.
Fig. 3 (d) shows the results of solution uptake in the CoWB/NF
catalyst. The solution uptake increased linearly with increasing
concentration from 5 wt % to 25 wt%. The main reason is that the
porous catalyst holds almost the same volume of solution, and the
more highly concentrated solution has a larger solution density.
3
3
.2. Catalytic performance
.2.1. Effect of the mole fraction of W/Co in the initial plating
These results and conclusions are beneficial for the design of H
2
solution
The effect of the mole fraction of W/Co in the initial plating
generators.
solution was studied, as shown in Fig. 3(aec). The as-prepared W-
4
3.4. Effect of NaBH concentration
doped alloy catalyst presents a high activity towards hydrolysis of
the NaBH
4
solution, but the catalytic activity is closely related to the
The rate of hydrogen generated versus the concentration of
NaBH in wt.% is given in Fig. 3 (e). The effect of NaBH concen-
tration on the hydrogen generation rate was measured using x wt. %
W content in the initial plating solution. This is because the XPS
spectrum of W 4f5 shifted when W was doped into the CoWB/NF
catalyst in the PED process, which led to different catalytic effects.
As shown in Fig. 3(a), the CoWB/NF catalyst with a W/Co mole
fraction of 40% shows the maximum catalytic activity. By using the
4
4
NaBH
4
(x ¼ 5, 10, 15, 20, 25, 30, 35) and 2 wt% NaOH solution at
ꢂ
30 C using CoWB/NF catalyst. As the NaBH
4
concentration
increased from 5 wt % to 35 wt%, the average hydrogen generation
rate decreased. The result is the same as that explained in the
optimized CoWB/NF catalyst, the 5 wt% NaBH
4
þ2 wt% NaOH
Fig. 3. (a) Effect of the mole fraction of W/Co in the initial solution on HGR at different temperatures. (b, c) Activation energy of the CoWB/NF catalyst at different mole fractions of
W/Co. (d) Solution uptake in the CoWB/NF catalyst. (e, f, g) H
the NaOH content in solution at different reaction temperatures (Typical conditions: 10 g of reaction solution includes 30 wt% NaBH
2 4
generation rate at different NaBH concentrations, NaOH contents, and reaction temperatures. (h) Influence curve of
þ2 wt% NaOH, 30 ꢂC).
4

Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
5
Fig. 4. BET surface area and pore size distribution.
ꢀ
1
ꢀ1
ꢀ1
ꢀ1 ꢀ1
Table 1
where k (L min
g
) is the rate coefficient, A (min
g
) is a
K )
Regression coefficients and activation energy at different W/Co ratios.
ꢀ1 ꢀ1
constant, Ea (kJ mol ) is the activation energy, R (8.314 J mol
is the universal gas constant, and T (K) is the temperature.
W/Co(%)
0
10
20
30
40
50
Parameter
The two parameters, Ln k and 1/T, are fitted linearly. The slope of
the linear equation equals e Ea/R, and the activation energy can be
calculated with the slope multiplied by eR.
Regression coefficients (%)
89.07 87.46 85.51 93.44 92.14 94.44
Activation Energy (kJ.molꢀ1) 29.15 26.86 26.36 19.57 18.15 19.74
4
The activation energy of hydrolysis of NaBH in the presence of
ꢂ
ꢂ
the CoWB/NF catalyst in the temperature range from 30 C to 70 C
is shown in Fig. 3 (c), and the value is as low as 18.15 kJ/mol in
contrast to 28 kJ/mol for Pd/C catalysts. The CoWB/NF catalyst had a
literature [44]. The main reason may be that the porous structure
caused the NaBH
catalyst with a higher solution viscosity at a higher NaBH
4
solution to diffuse to the surface of the CoWB/NF
con-
ꢀ
1
ꢀ1
ꢂ
high HGR, which reached 14.13 L min $g cat at 70 C (30 wt%
NaBH , 2 wt% NaOH) and was comparable to that of noble metal
4
centration, which is discouraging for hydrogen generation on the
interface between the catalyst and solution.
4
catalysts in the literature [21,46,54,56e60], as shown in Table 2. The
CoWB/NF catalyst shows ideal catalytic activity and lower activa-
tion energy, especially a long enough service life for hydrolysis of
sodium borohydride at different working concentration conditions.
The kinetic order of hydrolysis of the CWB/NF catalyst was
calculated by the n-order kinetics model in formula (3).
3.5. Effect of NaOH concentration
The effect of NaOH concentration on hydrogen production from
the hydrolysis of NaBH
4
has been studied. Fig. 3(f) illustrates the
hydrogen generation rate with different NaOH concentrations, i.e.,
dCNaBH4
dt
dCH2
dt
n
n
0
, 1, 2, 4, 8 wt %, in 10 g of NaBH
4
solution with 30 wt% NaBH
4
at
ꢀrNaBH4
¼
¼ kC
¼ 4kCH2 ¼ 4
¼ 4rH2
(4)
NaBH4
ꢂ
3
0 C. When the NaOH concentration increased from 0 wt % to 2 wt
%
, the HGR decreased rapidly. This phenomenon is well known and
can be explained [43] by the inhibition and stabilization effects of
the hydroxyl ions in the NaBH solution. Then, when the NaOH
The exponent of n is the reaction order. It is known that the
relationship between hydrogen generation volume and time is
linear. Therefore, the hydrogen generation rate and reaction rate of
4
concentration changed from 2 wt% to 8 wt%, the HGR increased and
remained steady. The reason is that OH is involved in the hydro-
4
NaBH are constant in the hydrolysis process of sodium borohy-
dride. The kinetic order n is zero, which indicates that it is a typical
zero-order reaction with the CWB/NF catalyst.
ꢀ
lysis of NaBH
decrease in NaBO
4
, and an increase in NaOH concentration leads to a
solubility and subsequent precipitation from the
2
solution and adherence on the catalyst surface. As a result, the
hydrolysis reaction is hindered. In addition, hydroxyl ions strongly
complex water, thus decreasing the available free water needed for
3
.7. Durability
Catalyst durability is a crucial parameter for a practical hydrogen
NaBH
4
hydrolysis [45].
generation apparatus. In the present study, the durability of the
CoWB/NF catalyst prepared by PED was tested in continuous
hydrogen production tests. After the catalytic hydrolysis reaction,
the catalyst was separated from the byproduct solution, washed
thoroughly with deionized water and reused. As seen in Fig. 5(a and
b), the effect of NaBH
better at higher NaBH
that, the CoWB/NF catalyst showed better durability in continuous
usage at a NaBH concentration of 30 wt% than at lower concen-
3.6. Effect of solution temperature and activation energy
The influence of temperature on the hydrogen generation rate in
solutions containing 30 wt% NaBH and 2 wt% NaOH was investi-
4
4
concentration was that the durability was
concentrations with 300 h of testing. After
ꢂ
ꢂ
gated at temperatures ranging from 30 C to 70 C, as shown in
Fig. 3(g and h). As expected, the hydrogen generation rate increases
with temperature. Decreasing the NaOH concentration had an
inhibitory effect at room temperature, and this effect was further
increased at higher solution temperatures.
4
4
trations. Fig. 5(c and d) shows that even after 800 h, the catalytic
activity could retain 82% HGR of its initial performance,
The activation energies are calculated and analyzed with the
reaction rates of the synthesized CoWB/NF catalyst at different
temperatures by using the Arrhenius equation as follows:
ꢀ1 ꢀ1
.41 L min $g (cat). The main reason for the decline was the
1
production of the major byproduct sodium metaborate that might
lead to a viscous solution to block the active catalytic sites and
paths for hydrogen evolution from the surface of the catalyst. TOF
Ln k ¼ ln A ꢀ Ea=RT
(3)
(turnover frequency) was used to measure the intrinsic activity of
the catalyst. The basic meaning is the amount of material catalyzed

6
Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
Table 2
A comparison of the HGR and Ea values of the CoWB/NF catalyst and the published results of other noble metal or nonnoble metal catalysts.
ꢂ
ꢀ1 ꢀ1
ꢀ1
(kJ$mol )
Catalyst
T ( C)
NaBH
4
(wt.%)
NaOH (wt.%)
HGR (L$min $g
)
E
a
Service life
Ref
Pt/C
Pd/C
Ru/NF
CoeB/C
CoeWeP/Cu
CoeB/NF
CoeNieMoeP/
CoeSneB/GP
CoWB/NF
40
25
30
30
30
20
30
30
30
10
1
5
10
10
25
7
5
5
30
30
5
5
2
5
10
3
10
5
2
2
23
23
23.03
10.82
5
e
e
[56]
[57]
[54]
[58]
[59]
[21]
[61]
[46]
28
3 h
100 cycles
e
39.48
56.7
22.8
e
5 cycles
2.3 h
5 cycles
e
7.2
g-Al
2
O
3
3.68
11.27
4.2
1.71
14.13
52.43
39.57
18.15
300 h
800 h
e
Our work
3
7
0
0
2
4
Fig. 5. Effect of NaBH concentration on catalytic durability.

Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
7
Fig. 6. (a) Photograph of the hydrogen generator. (b) Hydrogen generation rate and temperature of hydrogen gas. (c, d) Gas purity detection results from FID and TCD.
by a catalyst per unit mass per unit time. To calculate the TOF of the
CoWB active catalyst, we used the following formula:
nanodendrites with acicular arrays formed during the pulse
growing process, which increased the BET surface area, especially
provided more nanostructure pores. Therefore, the CoWB/NF
catalyst has an ideal hydrogen generation rate, and the HGR
The moles number of H2 turnover
Mass of catalyst ꢁ Time of reaction
TOF ¼
(5)
ꢀ
1
ꢀ1
reached 14.13 L min $g cat. Tungsten doping decreased the
ꢀ1
activation energy to as low as 18.15 kJ mol . The CoWB/NF catalyst
showed a superior hydrogen production stability of 300 h at
We calculated the TOF of CoWB in the service life process, and
the results are shown in Fig. 5(f).
4
different NaBH concentrations. The hydrogen production service
The SEM images of CoWB/NF after the 800-h stability test are
shown in Fig. 5(e). The nanostructures of the CoWB/NF catalyst do
not suffer from destruction, indicating that the nanostructures in
the CoWB/NF catalyst are very stable against aggregation and
destruction in the hydrolysis of sodium borohydride, which is the
same conclusion reported in the literature [62e67].
life was up to 800 h, and the catalyst demonstrated very good
stability, as the catalytic activity was maintained at 82%. The pulse
electrodeposition method can enhance the adhesion between the
catalyst and carrier of NF. The present work reveals that a CoWB
catalyst supported on NF could be used in practical NaBH ebased
4
hydrogen generators for portable fuel cell systems with high cat-
alytic activity and high durability.
3.8. Hydrogen generation performance in the generator
Declaration of competing interest
We designed and developed a hydrogen generator based on the
CoWB/NF catalyst, and a photograph is shown in Fig. 6 (a). The
diameter and height size of this cylindrical system are both 20 cm.
The hydrogen generation volume is linearly increased, and the rate
is steady; the average rate is 1.07 L/min, as shown in Fig. 6 (b). The
hydrogen gas purity was tested by gas chromatography, and the
results are shown in Fig. 6(c and d). The FID front signal shows three
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
CRediT authorship contribution statement
impurities: CH
The TCD back signal indicates that the main impurity is CO
0.0115%), and the hydrogen purity is H (99.9871%). The source of
impurities may come from the NaBH or NaOH raw material. The
purity is high enough to serve as the hydrogen source for a fuel cell,
and the hydrogen generation rate could supply hydrogen for a
4 2 6 2 4
(0.0005%), C H (0.0006%), and C H (0.0003%).
Yongsheng Wei: Visualization, Conceptualization, Methodol-
ogy. Maosen Wang: Data curation, Writing - original draft.
Wenying Fu: Visualization, Investigation. Lu Wei: Investigation.
Xinsheng Zhao: Validation. Xiangyang Zhou: Writing - review &
editing. Meng Ni: Supervision. Haijiang Wang: Supervision,
Validation.
2
(
2
4
100 W fuel cell system.
4
. Conclusions
Acknowledgments
A CoWB catalyst supported on NF was prepared by using the
This work was financially supported by the National Natural
pulse electrodeposition method. The special microstructure of
Science Foundation of China (No. 21606115), the Shenzhen Peacock

8
Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
Plan (KQTD2016022620054656), the Development and Reform
Commission of Shenzhen Municipality (2017) No. 1106 and the
Guangdong Innovative and Entrepreneurial Research Team Pro-
gram (2016ZT06N500). Prof. Meng Ni acknowledges a grant (Proj-
ect Number: PolyU 152214/17E) from the Research Grant Council,
University Grants Committee, Hong Kong SAR.
for the hydrolysis of sodium borohydride solutions to generate hydrogen for
PEM fuel cells, Int. J. Hydrogen Energy 33 (2008) 7095e7102.
26] Y.Q. Huang, Y. Wang, R.X. Zhao, P.K. Shen, Z.D. Wei, Accurately measuring the
hydrogen generation rate for hydrolysis of sodium borohydride on multi-
walled carbon nanotubes/Co-B catalysts, Int. J. Hydrogen Energy 33 (2008)
[
[
7110e7115.
27] N. Patel, R. Fernandes, G. Guella, A. Kale, A. Miotello, B. Patton, et al., Struc-
tured and nanoparticle assembled Co-B thin films prepared by pulsed laser
deposition: a very efficient catalyst for hydrogen production, J. Phys. Chem. C
1
12 (2008) 6968e6976.
References
[28] K. Eom, K. Cho, H. Kwon, Effects of electroless deposition conditions on mi-
crostructures of cobalt-phosphorous catalysts and their hydrogen generation
properties in alkaline sodium borohydride solution, J. Power Sources 180
(2008) 484e490.
[29] D.R. Kim, K.W. Cho, Y.I. Choi, C.J. Park, Fabrication of porous Co-Ni-P catalysts
by electrodeposition and their catalytic characteristics for the generation of
hydrogen from an alkaline NaBH4 solution, Int. J. Hydrogen Energy 34 (2009)
2622e2630.
[30] R. Fernandes, N. Patel, A. Miotello, Efficient catalytic properties of Co-Ni-P-B
catalyst powders for hydrogen generation by hydrolysis of alkaline solution
of NaBH4, Int. J. Hydrogen Energy 34 (2009) 2893e2900.
[31] R. Fernandes, N. Patel, A. Miotello, M. Filippi, Studies on catalytic behavior of
Co-Ni-B in hydrogen production by hydrolysis of NaBH4, J. Mol. Catal. Chem.
298 (2009) 1e6.
[
[
[
[
[
[
[
[
[
1] Y.T. Luo, L. Tang, U. Khan, Q.M. Yu, H.M. Cheng, X.L. Zou, et al., Morphology and
surface chemistry engineering toward pH-universal catalysts for hydrogen
evolution at high current density, Nat. Commun. 10 (2019) 1e9.
2] D. Bhattacharjee, S. Dasgupta, Trimetallic NiFePd nanoalloy catalysed
hydrogen generation from alkaline hydrous hydrazine and sodium borohy-
dride at room temperature, J. Mater. Chem. 3 (2015) 24371e24378.
3] S.H. Wang, Y.A. Fan, M.Q. Chen, Y.Y. Xie, D.W. Wang, C.Y. Su, Porous Co-P-Pd
nanotube arrays for hydrogen generation by catalyzing the hydrolysis of
alkaline NaBH4 solution, J. Mater. Chem. 3 (2015) 8250e8255.
4] T.T. Liu, K.Y. Wang, G. Du, A.M. Asiri, X.P. Sun, Self-supported CoP nanosheet
arrays: a non-precious metal catalyst for efficient hydrogen generation from
alkaline NaBH4 solution, J. Mater. Chem. 4 (2016) 13053e13057.
5] D.D. Tuan, K.Y.A. Lin, Ruthenium supported on ZIF-67 as an enhanced catalyst
for hydrogen generation from hydrolysis of sodium borohydride, Chem. Eng. J.
[32] N. Patel, R. Fernandes, A. Miotello, Hydrogen generation by hydrolysis of
NaBH4 with efficient Co-P-B catalyst: a kinetic study, J. Power Sources 188
(2009) 411e420.
351 (2018) 48e55.
6] Y. Kojima, K. Suzuki, K. Fukumoto, M. Sasaki, T. Yamamoto, Y. Kawai, et al.,
Hydrogen generation using sodium borohydride solution and metal catalyst
coated on metal oxide, Int. J. Hydrogen Energy 27 (2002) 1029e1034.
7] P. Krishnan, T.H. Yang, W.Y. Lee, C.S. Kim, PtRu-LiCoO2 - an efficient catalyst
for hydrogen generation from sodium borohydride solutions, J. Power Sources
[33] Y. Chen, H. Kim, Preparation and application of sodium borohydride com-
posites for portable hydrogen production, Energy 35 (2010) 960e963.
[34] K. Eom, H. Kwon, Effects of deposition time on the H-2 generation kinetics of
electroless-deposited cobalt-phosphorous catalysts from NaBH4 hydrolysis,
and its cyclic durability, Int. J. Hydrogen Energy 35 (2010) 5220e5226.
[35] X.W. Zhang, J.Z. Zhao, F.Y. Cheng, J. Liang, Z.L. Tao, J. Chen, Electroless-
deposited Co-P catalysts for hydrogen generation from alkaline NaBH4 solu-
tion, Int. J. Hydrogen Energy 35 (2010) 8363e8369.
[36] V.I. Simagina, O.V. Komova, A.M. Ozerova, O.V. Netskina, G.V. Odegova,
D.G. Kellerman, et al., Cobalt oxide catalyst for hydrolysis of sodium boro-
hydride and ammonia borane, Appl. Catal. a-Gen. 394 (2011) 86e92.
[37] T.H. Oh, S. Kwon, Effect of manufacturing conditions on properties of elec-
troless deposited Co-P/Ni foam catalyst for hydrolysis of sodium borohydride
solution, Int. J. Hydrogen Energy 37 (2012) 15925e15937.
[38] T.H. Oh, S. Kwon, Effect of bath composition on properties of electroless
deposited Co-P/Ni foam catalyst for hydrolysis of sodium borohydride solu-
tion, Int. J. Hydrogen Energy 37 (2012) 17027e17039.
[39] T.H. Oh, S. Kwon, Performance evaluation of hydrogen generation system with
electroless-deposited Co-P/Ni foam catalyst for NaBh(4) hydrolysis, Int. J.
Hydrogen Energy 38 (2013) 6425e6435.
143 (2005) 17e23.
8] Z.L. Liu, B. Guo, S.H. Chan, E.H. Tang, L. Hong, Pt and Ru dispersed on LiCoO(2)
for hydrogen generation from sodium borohydride solutions, J. Power Sources
176 (2008) 306e311.
9] S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, N.C. Spencer, M.T. Kelly,
P.J. Petillo, et al., A safe, portable, hydrogen gas generator using aqueous
borohydride solution and Ru catalyst, Int. J. Hydrogen Energy 25 (2000)
969e975.
[
[
10] S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, M.T. Kelly, P.J. Petillo,
M. Binder, An ultrasafe hydrogen generator: aqueous, alkaline borohydride
solutions and Ru catalyst, J. Power Sources 85 (2000) 186e189.
11] Z.T. Xia, S.H. Chan, Feasibility study of hydrogen generation from sodium
borohydride solution for micro fuel cell applications, J. Power Sources 152
(
2005) 46e49.
[
[
[
12] J.S. Zhang, W.N. Delgass, T.S. Fisher, J.P. Gore, Kinetics of Ru-catalyzed sodium
borohydride hydrolysis, J. Power Sources 164 (2007) 772e781.
13] U.B. Demirci, F. Garin, Ru-based bimetallic alloys for hydrogen generation by
hydrolysis of sodium tetrahydroborate, J. Alloys Compd. 463 (2008) 107e111.
14] Y. Liang, H.B. Dai, L.P. Ma, P. Wang, H.M. Cheng, Hydrogen generation from
[40] J.H. Kim, K.T. Kim, Y.M. Kang, H.S. Kim, M.S. Song, Y.J. Lee, et al., Study on
degradation of filamentary Ni catalyst on hydrolysis of sodium borohydride,
J. Alloys Compd. 379 (2004) 222e227.
[41] A.M.F.R. Pinto, D.S. Falcao, R.A. Silva, C.M. Rangel, Hydrogen generation and
storage from hydrolysis of sodium borohydride in batch reactors, Int. J.
Hydrogen Energy 31 (2006) 1341e1347.
sodium borohydride solution using
catalyst, Int. J. Hydrogen Energy 35 (2010) 3023e3028.
a ruthenium supported on graphite
[
[
[
15] Y.H. Huang, C.C. Su, S.L. Wang, M.C. Lu, Development of Al2O3 carrier-Ru
composite catalyst for hydrogen generation from alkaline NaBH4 hydrolysis,
Energy 46 (2012) 242e247.
16] Z.M. Huang, A. Su, Y.C. Liu, Hydrogen generator system using Ru catalyst for
PEMFC (proton exchange membrane fuel cell) applications, Energy 51 (2013)
[42] Q.L. Zhang, Y. Wu, X.L. Sun, J. Ortega, Kinetics of catalytic hydrolysis of sta-
bilized sodium borohydride solutions, Ind. Eng. Chem. Res. 46 (2007)
1120e1124.
[43] H.J. Tian, Q.J. Guo, D.Y. Xu, Hydrogen generation from catalytic hydrolysis of
alkaline sodium borohydride solution using attapulgite clay-supported Co-B
catalyst, J. Power Sources 195 (2010) 2136e2142.
[44] E. Ozdemir, Enhanced catalytic activity of Co-B/glassy carbon and Co-B/
graphite catalysts for hydrolysis of sodium borohydride, Int. J. Hydrogen En-
ergy 40 (2015) 14045e14051.
230e236.
17] S.U. Jeong, R.K. Kim, E.A. Cho, H.J. Kim, S.W. Nam, I.H. Oh, et al., A study on
hydrogen generation from NaBH4 solution using the high-performance Co-B
catalyst, J. Power Sources 144 (2005) 129e134.
[
18] C. Wu, F. Wu, Y. Bai, B.L. Yi, H.M. Zhang, Cobalt boride catalysts for hydrogen
generation from alkaline NaBH4 solution, Mater. Lett. 59 (2005) 1748e1751.
19] N. Patel, G. Guella, A. Kale, A. Miotello, B. Patton, C. Zanchetta, et al., Thin films
of Co-B prepared by pulsed laser deposition as efficient catalysts in hydrogen
producing reactions, Appl. Catal. a-Gen. 323 (2007) 18e24.
[45] Y. Wang, T.L. Li, S.C. Bai, K.Z. Qi, Z.Q. Cao, K. Zhang, et al., Catalytic hydrolysis of
sodium borohydride via nanostructured cobalt-boron catalysts, Int. J.
Hydrogen Energy 41 (2016) 276e284.
[46] Z.K. Cui, Y.P. Guo, J.T. Ma, In situ synthesis of graphene supported Co-Sn-B
alloy as an efficient catalyst for hydrogen generation from sodium borohy-
dride hydrolysis, Int. J. Hydrogen Energy 41 (2016) 1592e1599.
[47] Y. Liang, P. Wang, H.B. Dai, Hydrogen bubbles dynamic template preparation
of a porous Fe-Co-B/Ni foam catalyst for hydrogen generation from hydrolysis
of alkaline sodium borohydride solution, J. Alloys Compd. 491 (2010)
359e365.
[48] O.V. Komova, V.I. Simagina, O.V. Netskina, D.G. Kellerman, A.V. Ishchenko,
N.A. Rudina, LiCoO(2)-based catalysts for generation of hydrogen gas from
sodium borohydride solutions, Catal. Today 138 (2008) 260e265.
[49] A.M.F.R. Pinto, M.J.F. Ferreira, V.R. Fernandes, C.M. Rangel, Durability and
reutilization capabilities of a Ni-Ru catalyst for the hydrolysis of sodium
borohydride in batch reactors, Catal. Today 170 (2011) 40e49.
[50] H.B. Dai, Y. Liang, P. Wang, Effect of trapped hydrogen on the induction period
of cobalt-tungsten-boron/nickel foam catalyst in catalytic hydrolysis reaction
of sodium borohydride, Catal. Today 170 (2011) 27e32.
[
[
[
[
20] K.W. Cho, H.S. Kwon, Effects of electrodeposited Co and Co-P catalysts on the
hydrogen generation properties from hydrolysis of alkaline sodium borohy-
dride solution, Catal. Today 120 (2007) 298e304.
21] J. Lee, K.Y. Kong, C.R. Jung, E. Cho, S.P. Yoon, J. Han, et al., A structured Co-B
catalyst for hydrogen extraction from NaBH4 solution, Catal. Today 120
(
2007) 305e310.
22] M. Mitov, R. Rashkov, N. Atanassov, A. Zielonka, Effects of nickel foam di-
mensions on catalytic activity of supported Co-Mn-B nanocomposites for
hydrogen generation from stabilized borohydride solutions, J. Mater. Sci. 42
(
2007) 3367e3372.
[
23] S.J. Kim, J. Lee, K.Y. Kong, C.R. Jung, I.G. Min, S.Y. Lee, et al., Hydrogen gener-
ation system using sodium borohydride for operation of a 400 W-scale
polymer electrolyte fuel cell stack, J. Power Sources 170 (2007) 412e418.
24] H.B. Dai, Y. Liang, P. Wang, X.D. Yao, T. Rufford, M. Lu, et al., High-performance
cobalt-tungsten-boron catalyst supported on Ni foam for hydrogen genera-
tion from alkaline sodium borohydride solution, Int. J. Hydrogen Energy 33
[
[51] A. Ekinci, O. Sahin, C. Saka, T. Avci, The effects of plasma treatment on elec-
trochemical activity of Co-W-B catalyst for hydrogen production by hydrolysis
of NaBH4, Int. J. Hydrogen Energy 38 (2013) 15295e15301.
(
2008) 4405e4412.
[25] P. Krishnan, S.G. Advani, A.K. Prasad, Cobalt oxides as Co2B catalyst precursors
[52] Y.S. Wei, R. Wang, L.Y. Meng, Y. Wang, G.D. Li, S.G. Xin, et al., Hydrogen

Y. Wei et al. / Journal of Alloys and Compounds 836 (2020) 155429
9
generation from alkaline NaBH4 solution using a dandelion-like Co-Mo-B
catalyst supported on carbon cloth, Int. J. Hydrogen Energy 42 (2017)
[60] Y.P. Guo, Z.P. Dong, Z.K. Cui, X.J. Zhang, J.T. Ma, Promoting effect of W doped in
electrodeposited Co-P catalysts for hydrogen generation from alkaline NaBH4
solution, Int. J. Hydrogen Energy 37 (2012) 1577e1583.
9945e9951.
[
[
53] Y.S. Wei, X.K. Huang, J.Y. Wang, H.Y. Yu, X.S. Zhao, D.J. Cheng, Synthesis of
bifunctional non-noble monolithic catalyst Co-W-P/carbon cloth for sodium
borohydride hydrolysis and reduction of 4-nitrophenol, Int. J. Hydrogen En-
ergy 42 (2017) 25860e25868.
54] Y.S. Wei, Y. Wang, L. Wei, X.S. Zhao, X.Y. Zhou, H.T. Liu, Highly efficient and
reactivated electrocatalyst of ruthenium electrodeposited on nickel foam for
[61] L.N. Wang, Z. Li, P.P. Zhang, G.X. Wang, G.W. Xie, Hydrogen generation from
alkaline NaBH4 solution using Co-Ni-Mo-P/gamma-Al2O3 catalysts, Int. J.
Hydrogen Energy 41 (2016) 1468e1476.
[62] H. Li, J.Y. Liao, R.F. Wang, Controlled synthesis of nanostructured Co film
catalysts with high performance for hydrogen generation from sodium
borohydride solution, J. Power Sources 239 (2013) 277e283.
hydrogen evolution from NaBH
2018) 592e600.
4
alkaline solution, Int. J. Hydrogen Energy 43
[63] J.J. Yan, J.Y. Liao, H. Li, H. Wang, R.F. Wang, Magnetic field induced synthesis of
amorphous CoB alloy nanowires as a highly active catalyst for hydrogen
generation from ammonia borane, Catal. Commun. 84 (2016) 124e128.
[64] X.P. Wang, J.Y. Liao, H. Li, H. Wang, R.F. Wang, Solid-state-reaction synthesis of
cotton-like CoB alloy at room temperature as a catalyst for hydrogen gener-
ation, J. Colloid Interface Sci. 475 (2016) 149e153.
[65] D.S. Lu, J.Y. Liao, Y. Leng, S.D. Zhong, J.N. He, H. Wang, R.F. Wang, H. Li, Mo-
doped Cu0.5Ni0.5Co2O4 nanowires, a strong substitute for noble-metal-based
catalysts towards the hydrolysis of ammonia borane for hydrogen production,
Catal. Commun. 114 (2018) 89e92.
[66] A. Balbay, C. Saka, The effect of the concentration of hydrochloric acid and
acetic acid aqueous solution for fast hydrogen production from methanol
solution of NaBH4, Int. J. Hydrogen Energy 43 (2018) 14265e14272.
[67] M. Bekirogullari, M. Kaya, C. Saka, Highly efficient Co-B catalysts with
Chlorella Vulgaris microalgal strain modified using hydrochloric acid as a new
support material for hydrogen production from methanolysis of sodium
borohydride, Int. J. Hydrogen Energy 44 (2019) 7262e7275.
(
[
[
55] J.L. Wang, F.Y. Chen, Y.C. Jin, Y.M. Lei, R.L. Johnston, One-pot synthesis of
dealloyed AuNi nanodendrite as a bifunctional electrocatalyst for oxygen
reduction and borohydride oxidation reaction, Adv. Funct. Mater. 27 (2017).
56] Y.J. Ma, R.F. Wang, H. Wang, V. Linkov, S. Ji, Evolution of nanoscale amorphous,
crystalline and phase-segregated PtNiP nanoparticles and their electro-
catalytic effect on methanol oxidation reaction, Phys. Chem. Chem. Phys. 16
(
2014) 3593e3602.
[
57] Y. Bai, C.A. Wu, F. Wu, B.L. Yi, Carbon-supported platinum catalysts for on-site
hydrogen generation from NaBH4 solution, Mater. Lett. 60 (2006) 2236e2239.
58] N. Patel, B. Patton, C. Zanchetta, R. Fernandes, G. Guella, A. Kale, et al., Pd-C
powder and thin film catalysts for hydrogen production by hydrolysis of so-
dium borohydride, Int. J. Hydrogen Energy 33 (2008) 287e292.
59] F. Baydaroglu, E. Ozdemir, A. Hasimoglu, An effective synthesis route for
improving the catalytic activity of carbon-supported Co-B catalyst for
hydrogen generation through hydrolysis of NaBH4, Int. J. Hydrogen Energy 39
[
[
(
2014) 1516e1522.