Self-template synthesis of hierarchical CoMoS3 nanotubes constructed of ultrathin nanosheets for robust water electrolysis

Article abstract of DOI:10.1039/c7ta02768k

Exploration of pH-universal and durable catalysts with specific structure and high performance is desirable but challenging for electrochemical water splitting. Aiming at this goal, hierarchical CoMoS₃ nanotubes constructed of ultrathin nanosheet subunits are prepared via a self-sacrifice template method. The conversion from CoMoO₄ nanorods to hierarchical MoCoS₃ nanotubes is successfully realized through a facile solvothermal process. The obtained sample simultaneously possesses advanced structural superiority and synergism of ternary Co-Mo-S. Endowed with these advantages, MoCoS₃ can serve as a pH-universal and high-performance electrocatalyst for hydrogen evolution, delivering low onset overpotential, small overpotential required to generate current density of 10 mA cm^-2, and good stability. Moreover, it exhibits excellent catalytic performance in the electrochemical oxygen evolution reaction, making it a promising dual-functional catalyst for water electrolysis.

Full text of DOI:10.1039/c7ta02768k

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January 2016 Pages 1–330
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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

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Journal of Materials Chemistry A
►
Journal Name
ARTICLE TYPE
Self-template synthesis of hierarchical CoMoS nanotubes constructed
3
by ultrathin nanosheets for robust water electrolysis
a
a
b
a
a,
Jinxue Guo , Xinqun Zhang , Yanfang Sun , Lin Tang , Xiao Zhang
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x

Corresponding author. Tel.: +86 532 84022681; Fax: +86 532 84023927.
E-mail address: zhx1213@126.com (X. Zhang).
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Journal Name
ARTICLE TYPE
Exploration of pH-universal and durable catalysts with
specific structure and high-performance is desirable but
challenging for electrochemical water splitting. Aiming at this
goal, hierarchical CoMoS3 nanotubes constructed by
ultrathin nanosheet subunits are prepared via a self-sacrifice
doping Co heteroatoms into MoS
demonstrated improved catalytic activity.
al. have recently reported the synthesis of ternary M-MoS
Co, Ni) hollow structures for robust electrocatalytic hydrogen
production. Despite these aforementioned progresses, the
rational design and construction of hierarchical 3D architectures
2
have been prepared and
2
6-30
For example, Yu et
(M =
3
5
6
6
7
7
8
8
9
9
5
0
5
0
5
0
5
0
5
2
8
5
0
5
template method. The conversion from CoMoO nanorods to
4
constructed by ternary Co-Mo-S nanosheets as dual-functional
x
hierarchical MoCoS3 nanotubes is successfully realized
through a facile solvothermal process. The obtained sample
simultaneously possesses advanced structural superiority and
synergism of ternary Co-Mo-S. Endowed with these
catalysts, which possess combined advantages for catalytic
activity of highly exposed active edge sites, synergistic effect
between Co and Mo, and large specific surface area, have rarely
been reported and still remain a big challenge.
In the present work, we developed a novel self-sacrifice
template method to prepare hierarchical CoMoS3 nanotubes
constructed by ultrathin nanosheets through a facile solvothermal
1
advantages, MoCoS can serve as the pH-universal and high-
3
performance electrocatalysts for hydrogen evolution,
delivering low onset overpotential, small overpotential
-
2
required to generate current density of 10 mA cm , and good
stability. Moreover, it exhibits excellent catalytic performance
in electrochemical oxygen evolution reaction, making it a
promising dual-functional catalyst for water electrolysis.
process using CoMoO nanorods as precursors. The specific 3D
4
1
hollow tubular architecture constructed by hierarchical 2D
nanosheets possesses merits of exposed active edge sites, large
surface area, fluent electrolyte transport, as well as intrinsic
catalytic activity, delivering enhanced electrocatalytic
performance in terms of large catalytic current density, small
overpotentials, and good stability for both the HER and OER
production. More importantly, the present catalyst exhibits
excellent HER electrocatalytic performances in both acidic and
alkaline electrolyte, making it a promising pH-universal cathode
catalyst for water electrolysis.
Introduction
Hydrogen energy has been considered as the most promising
2
2
3
3
4
4
5
0
5
0
5
0
5
0
clean and renewable energy source facing the fossil fuels
1
exhaustion and environmental pollutions. Electrochemical water
splitting is one of the effective solutions for sustainable hydrogen
production, which consists of the cathodic hydrogen evolution
2
reaction (HER) and anodic oxygen evolution reaction (OER).
However, the large scale commercialization of water electrolysis
is hampered by the lack of cost-effective and high-performance
catalysts, the pH-intolerant cathode materials, and the limited
lifetimes of electrode materials. At present, various transition
Experiment
The CoMoO nanorods are obtained via a previously reported
4
31
hydrothermal method. Typically, 1.5 mmol of Co(NO ) ·6H O
3
2
2
and 1.5 mmol of Na MoO ·2H O are dissolved in 30 mL of water,
2
4
2
metal sulfides, especially MoS , have been widely used to
2
which is transferred into an autoclave of 50 mL and heated at 180
3
-6
catalyze the water splitting. It is widely believed that, the active
o
C for 12 h. The resultant precipitate is collected with
7
-10
sites of MoS catalyst only locate at the edge plane. Therefore,
2
centrifugation, washed with ethanol and water in turn, and then
MoS -based nanostructures with exposed edge sites or engineered
o
2
vacuum dried at 60 C. 100 mg of the resultant CoMoO4
defect sites have been widely developed to pursue improved
nanorods and 300 mg of thioacetamide are dispersed into 30 mL
of ethanol with ultrasonic treatment. The dispersion is transferred
1
1-14
catalytic activity.
In recent years, three-dimensional (3D) hierarchical
architectures have received intensive attention due to the
structural advantages, paving the way in the applications of
o
in an autoclave of 50 mL for heating at 150 C for 24 h. The
powders are collected, washed, dried, and then heated in a tube
o
furnace at 400 C for 3 h in Ar atmosphere with a heating rate of
1
5-20
energy conversion and storage.
Specifically, hollow
o
1
C per minute to obtain the final products.
micro/nanostructures with well-defined interior voids can
facilitate mass/electron transfer and expose active edge sites to
Scanning electron microscope (SEM) is characterized with a
JEOL JSM-7500F. Transmission electron microscope (TEM),
high-resolution TEM (HRTEM), and the corresponding energy
dispersive X-ray spectroscopy (EDX) are obtained on a FEI
Tecnai G2 F30. Raman spectroscopy is recorded on a confocal
microprobe Raman system (LabRam-e010, 632 nm as the
excitation source). X-ray photoelectron spectra (XPS) are
collected on a RBD upgraded PHI-5000c ESCA system (Perkin
promote electrocatalytic activity. For instance, MoS nanosheets
2
constructed 3D nanotubes have been synthesized by Wang et al.,
which exhibit excellent lithium storage properties as anode
1
5
materials. Zhang and co-workers have demonstrated the
fabrication of hierarchical MoS2 microboxes assembled with
nanosheets, which showed enhanced electrochemical properties
2
0
for lithium storage and water splitting.
On the other hand, quite a few reports have shown that cobalt
1
00 Elmer). The crystallographic information of CoMoS nanosheets
3
constructed nanotubes is collected from powder X-ray diffraction
2
1-25
suflides are promising electrocatalysts for HER activity.
To
(
XRD, Philips X’-pert X-ray diffactometer). The total specific
surface is measured with the multipoint Braunauer-Emmett-Teller
BET) method.
combine the fascinating advantages of Mo and Co based sulfides,
the so-called ternary metal sulfides of Co-Mo-S prepared by
x
(
This journal is © The Royal Society of Chemistry [year]
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DOI: 10.1039/C7TA02768K
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Journal of Materials Chemistry A
The electrochemical measurements are performed on
CHI760D (CH Instruments, Shanghai, China) using
conventional three-electrode configuration. A glassy carbon (GC)
electrode serves as the working electrode. Graphite rod is used as
the counter electrode. Saturated calomel electrodes (SCE) is used
as the reference electrode. The catalyst ink is obtained by mixing
significantly because it is entirely constructed by nanosheets (Fig.
1b). Interestingly, typical hollow tubular structure is clearly
observed in Fig. 1c. The hollow interior and hierarchical tubular
structure is further revealed by TEM image (Fig. 1d).
a
5
0
5
0
5
50
55
60
65
70
4
mg of hierarchical CoMoS nanotubes with 50 uL of Nafion
3
solution (5 wt.%) and 1.25 mL of water, which is then drop-
casted onto a glassy carbon electrode with the catalyst loading of
-
2
1
1
2
2
~ 0.5 mg cm . The HER tests are evaluated by linear sweep
voltammetry (LSV) tests in 0.5 M H SO4 and 1.0 M KOH,
2
respectively. The OER activity is tested in 1.0 M KOH. The
-
1
polarization curves are performed at a scan rate of 2 mV s . The
stability test is conducted using a rotating disk electrode with a
rotation speed of 1000 rpm for 10 h. The potentials are calibrated
by a reversible hydrogen electrode (RHE). Noting that, the
-
2
potential at a HER or OER current density of 1 mA cm is
defined as the onset potential. The electrochemical impedance
spectroscopy (EIS) tests are performed at the frequency range of
0.1 Hz to 100 kHz.
The electrochemical double-layer capacitance (Cdl)
measurements are performed on the potential range where no
faradic processes at varied scan rates of 20, 40, 60, 80, 100, 120,
-
1
and 140 mV s . The electrochemically active surface area (ECSA)
2
6
is determined from the obtained specific capacitance. The per
site turnover frequency (TOF) is also calculated based on the
Fig. 2 (a) Low and (b,c) high magnification TEM images of hierarchical
3
2
specific current density.
CoMoS
EDX elemental mapping images of S, Co, and Mo of the as-obtained
hierarchical CoMoS nanotubes.
3
nanotubes assembled with nanosheets. (d-g) TEM image and
Results and discussion
3
7
8
8
5
0
5
The hierarchical architecture of the ultrathin CoMoS3
nanosheets assembled nanotubes are detailedly characterized by
TEM. In Fig. 2a, the uniform nanotubes assembled by nanosheets
are clearly obtained. Closer examination of a tube clearly
indicates that the hierarchical CoMoS3 nanotube is indeed
composed of randomly oriented ultrathin nanosheets. The shell
thickness of the CoMoS nanotubes is estimated to be about 50
3
nm. This specific nanosheets assembled tubular structure assures
2
-1
a high BET surface area of 101 m g (Fig. S2), offering merits of
exposed active edge sites and large contact area for HER. Fig. 2c
displays the high-resolution TEM image of the rim of a tube in
Fig. 2a. Clearly, the interlaced “threads” corresponding to the
3
3
4
4
0
5
0
5
CoMoS
nanosheets with 2-4 packing layers are observed,
3
3
Fig. 1 Illustration of the synthesis of hierarchical CoMoS nanotubes
indicating the ultrathin nanosheets with abundant catalytic sites.
composed of ultrathin nanosheets from CoMoO
4
nanorods. SEM images 90 This is consistent with the XRD analysis (Fig. S1b). The reduced
(002) diffraction peak of CoMoS should be related to the
of (a) CoMoO and (b,c) CoMoS . (d) TEM image of CoMoS
4
3
3
.
3
depressed layer stack. It is demonstrated that the CoMoS3
nanosheets in the hierarchical hollow architecture only possess a
few layers. The ultrathin nanosheets assembled hierarchical
The formation process of hierarchical CoMoS3 nanotubes
composed of ultrathin nanosheet subunits, using CoMoO4
1
5
nanorods as precursors, is schematically shown in Fig. 1. The 95 tubular structures assure the high exposure of active edge sites
CoMoO4 nanorods with diameters of 150-200 nm are firstly
prepared via a simple hydrothermal method as the precursors (Fig.
1a and S1a). Then the precursors are used as self-sacrifice
template for the synthesis of CoMoS3 through a solvothermal
and good catalytic performance. The interlayer distance of 0.75
nm is determined for CoMoS , which is larger than that of 0.63
nm for MoS due to the Co doping, which is beneficial for robust
catalytic performance.
3
2
1
4,33
It is also in accordance with the (002)
sulfidation process. In the SEM images of Fig. 1b and c, the 100 diffraction peak in Fig. S1b. The EDX elemental mapping images
obtained CoMoS3 displays uniform one-dimensional (1D)
nanostructures. In comparison with the original CoMoO4
nanorods, the surface roughness of 1D CoMoS3 increases
(Fig. 2e-g) are recorded to further disclose the element
distributions of Co, Mo, and S. The three elements are distributed
homogeneously in the obtained hierarchical nanotubes,

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DOI: 10.1039/C7TA02768K
Journal of Materials Chemistry A
Page 4 of 8
confirming the successful formation of CoMoS3. The
corresponding EDX spectrum (Fig. S3) shows that the obtained
sample is composed of S, Co, and Mo elements with the atomic
ratio of 62.7 : 18.1 : 19.2, which are in good agreement with the
stoichiometric ratio of 3 : 1 : 1.
60
5
0
5
0
5
0
5
0
5
0
5
65
1
1
2
2
3
3
4
4
5
5
Fig. 4 HER performance of hierarchical CoMoS
SO : (a) Polarization curves of MoS , CoS , CoMoS
CoMoS nanotubes, and Pt/C electrodes in 0.5 M H SO . (b) Tafel plots,
c) time-dependent current density curve under static overpotential of 145
mV, (d) polarization curve after continuous durability test of 10 h.
Electrochemical capacitance measurements of hierarchical CoMoS
nanotubes: (e) measured capacitive currents plotted as the function of
scan rate, (f) The EIS spectra of MoS , CoS , CoMoS nanoparticles and
CoMoS nanotubes,. The inset in (f) shows the corresponding TOF value.
3
nanotubes in 0.5 M
7
7
8
0
5
0
H
2
4
2
2
3
nanoparticles,
3
2
4
(
Fig. 3 (a) Survey XPS spectrum of hierarchical CoMoS
resolution XPS spectra of (b) Mo 3d and S 2s, (c) Co 2p, and (d) S 2p of
hierarchical CoMoS nanotubes.
3
nanotubes. High
3
3
2
2
3
To probe the chemical states of Co, Mo, and S elements in
hierarchical CoMoS3 nanotubes, the XPS measurements are
performed. The XPS survey spectrum (Fig. 3a) shows the
overview of the chemical species, in which the XPS peaks
associated with S, Co, Mo, C, and O elements are detected. Fig.
3
The obtained hierarchical CoMoS3 nanotubes serve as dual
catalysts for water electrolysis. Generally, the HER performance
of metal sulfides is achieved in sulfuric acid solution. Therefore,
we firstly measured the electrocatalytic HER activity of
hierarchical CoMoS nanotubes in 0.5 M H SO using a three-
electrode system. Fig. 4a displays the HER polarization curves of
85 various catalysts, and Pt/C electrode is also supplied for
comparison. The MoS (Fig. S5a) and CoS (Fig. S5b) catalysts
show poor catalytic activity. Interestingly, CoMoS particles (Fig.
S5c) deliver improved catalytic performance than pristine MoS2
and CoS , indicating the synergistic effect between Co and Mo in
90 ternary sulfides. The doped Co atoms in MoS tend to substitute
the Mo atoms, resulting in unsaturated
unsaturated S atoms serve as active sites to enhance the HER
activity. The formation of Co-Mo-S can reduce the hydrogen
adsorption energy to 0.10 eV, which is much lower than that of
0.18 eV for Mo-S edges and could weaken the hydrogen
adsorption, thus greatly facilitating the proton adsorption kinetics
and hydrogen evolution. In comparison with CoMoS particles,
remarkably enhanced catalytic activity is obtained from CoMoS3
nanotubes, due to the specific structural advantages. CoMoS3
00 exhibits efficient electrocatalytic HER performance with a low
onset overpotential of about 80 mV, beyond which the cathodic
current increases rapidly when the potential negatively shifts.
This value is equal to the best value of 75 mV in Ref. 28, which is
the best result for Co-Mo-Sx catalysts to our knowledge.
05 Importantly, the η10 (the potential required to afford a current
3
b shows the high-resolution XPS spectra of Mo 3d and S 2s
3
4
peaks. The peak of 226.4 eV is assigned to the S 2s. Two well
defined peaks with binding energies of 229.3 and 232.5 eV
correspond to Mo 3d5/2 and Mo 3d3/2, respectively, indicating
the presence of Mo state.
eV is attributed to the Mo state, which is due to the partial
oxidation of exposed Mo . The Co 2p spectrum (Fig. 3c)
includes two regions of Co 2p and Co 2p1/2, which is consistent
with the previous reports.
from the CoMoS phase.
are ascribed to Co state. In the S 2p spectrum in Fig. 3d, the
peaks at 162.1 and 163.2 eV are assigned to the S 2p and S
3
2
4
4
+
12,34,35
The weak peak located at 236
6
+
2
2
4
+ 28
3
2
4-36
/3
3
2
The peak located at 779.1 eV is
And the peaks of 781.6 and 791.8 eV
3
4,35
2
2
+
S atoms. These
3
/2
3
0
2
- 34-36
2
p1/2 orbitals of S .
The XPS analysis indicates the formation
of CoMoS . The CoMoS phase is further confirmed by Raman
3
3
9
5
spectrum (Fig. S4), in which all the vibrational modes are well
2
8,34
consistent with the previous results of CoMoS3.
Moreover, the
3
XRD peaks associated with CoMoO are totally absent in the
4
XRD spectrum of CoMoS3 (Fig. S1b), showing the complete
transformation from CoMoO to CoMoS .
4
3
1
1
-
2
density of 10 mA cm ) for CoMoS is only 143 mV, which is
3
much lower than most of the reported MoS -based HER catalysts
2
8
in H SO solution, such as amorphous MoS2 (200 mV),
2
4

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Page 5 of 8
Journal of Materials Chemistry A
1
2
graphene quantum dots (GQDs) doped MoS (200 mV), MoS2-
performance of catalysts. In the inset of Fig. 4e, CoMoS3
2
27
37
CoMo S /graphene (181 mV), metallic MoS (187 mV),
MoO @MoS nanowires (235 mV), and MoS /CNT-graphene
255 mV). The detailed comparison is shown in Fig. S6, in
60 nanotubes exhibit much higher TOF values than MoS (Fig. S9d)
2
4
2
2
3
8
at high potential region, showing that CoMoS3 possesses
3
2
2
3
9
8,32
(
improved intrinsic catalytic activity for per catalytic site,
5
0
5
0
5
0
5
0
5
0
5
which the η10 of 143 mV for our present hierarchical CoMoS3
nanotubes is among the best results, including amorphous
assigning to synergistic effect of ternary Co-Mo-S . Moreover,
the HER reaction kinetics are probed by EIS technique. The arc
x
3
6
40
CoMoS (143 mV), edge terminated MoS (149 mV), Ni-Co- 65 in the Nyquist plots (Fig. 4f) is associated with the charge transfer
4
2
3
4
MoS2 nanoboxes (155 mV), O-doped MoS /graphene (163
mV), MoS /N-doped carbon nanoboxes (165 mV), and M–
MoS3 (M = Co, Ni) hollow structures (171 mV), which is
resistance. Clearly, CoMoS particles deliver much lower charge
2
3
3
3
41
resistance than MoS and CoS , due to the formation of ternary
2
2
2
2
8
1
1
2
2
3
3
4
4
5
5
Co-Mo-S. For CoMoS nanotubes, the charge resistance is further
3
slightly junior than the hybrid MoS /carbon catalysts, such as
decreased, assigned to the specific architecture.
2
4
2
MoS /N-doped CNT (110 mV) and Li-MoS /carbon fiber (118
70
2
2
4
3
-1
mV). In Fig. 4b, the corresponding Tafel slope of 78 mV dec
supplies the favorable kinetics, which corresponds to the Volmer-
Heyrovsky mechanism.
2
8,33,34
Durable stability is another important criterion for good
electrocatalysts. To estimate it, the long-term stability test is
75
performed by prolonging water electrolysis at
a fixed
overpotential of 145 mV (Fig. 4c). The current density of
CoMoS nanotubes shows small fade from the initial 10.7 mA
3
-
2
-2
cm to that of 9.8 mA cm after 10 h, delivering a relative high
current retention of 91.2%. After the long-term durability test,
80
CoMoS nanotubes are characterized with SEM (Fig. S7a) and
3
TEM (Fig. S7b). One can see that the structure of hierarchical
nanocubes can be maintained with slight degradation, which
should be responsible for the good catalytic stability of our
sample. The atomic ratio of 62.3 : 18.4 : 19.3 is collected with
EDX technique for S, Co, and Mo elements, which is similar to
the value for freshly prepared CoMoS3 nanotubes, further
confirming the good stability of the catalysis. Additionally, the
LSV polarization curve is also collected from the electrode after
85
Fig. 5 HER performance of CoMoS
3
in 1 M KOH: (a) Polarization curves
nanotubes, and Pt/C
continuous 10 h durability test. One can see from Fig. 4d that, the 90 of MoS
2
, CoS , CoMoS nanoparticles, CoMoS
2
3
3
CoMoS exhibits similar polarization curve in comparison with
electrodes in 1 M KOH, (b) Tafel plots, (c) time-dependent current
density curve under static overpotential of 135 mV, (d) polarization curve
after continuous durability test of 10 h.
3
the initial cycle. A low η10 of 169 mV can be retained after
durability test of 10 h, showing a small fade of 26 mV. All these
characterizations indicate the good catalytic stability of the
hierarchical CoMoS3 nanotubes. The amount of generated
hydrogen is quantitatively measured by gas chromatography
95
The electrochemical HER performance of hierarchical CoMoS3
nanotubes is also measured in 1.0 M KOH solution. In Fig. 5a, no
obvious HER activity can be obtained from MoS2 and CoS2
(GC), which is compared with the theoretically calculated
amounts of hydrogen to determine the Faradaic efficiency (FE).
The good agreement of the two sets of values (Fig. S8) shows the
high FE of nearly 100%.
Concluded from the above results, the formation of ternary
metal sulfides should be partially responsible for the improved
catalytic activity of the present sample. Besides, there are other
origins contributing to the enhanced HER performance,
catalysts. The evident catalytic activity of CoMoS particles is
3
assigned to the synergistic effect derived from the ternary metal
100 sulfides of Co-Mo-S. The improved activity of CoMoS3
nanotubes than CoMoS particles is due to the specific structural
3
advantages. CoMoS nanotubes deliver the onset overpotential at
3
about 65 mV, which is even lower than its onset potential for
HER in 0.5 M H SO . When the potential further shifts to
2
4
especially the structural advantages of the specific nanosheets 105 negative region, the cathodic current density increases sharply,
constructed tubular architecture. To reveal this, the double-layer
-
2
achieving a current density of 10 mA cm at the overpotential of
capacitance of CoMoS nanotubes is measured. Based on this, the
133 mV. This value is also lower than the η10 of 143 mV in acidic
3
corresponding electrochemical surface area and per site turnover
solution. Because the HER catalytic performance of MoS -based
2
frequency are obtained. Clearly, CoMoS nanotubes (Fig. S9a)
catalysts in alkaline solution has rarely been reported, we
3
deliver much higher non-faradic capacitive current than MoS2 110 compare the overpotential required to generate a current density
-
2
(
Fig. S9b). In Fig. 4e, CoMoS nanotubes exhibit an extremely
of 10 mA cm (η ) between our sample and other reported
3
10
-
2
-2
higher C of 11640 μF cm than pristine MoS (662 μF cm , Fig.
electrocatalysts in alkaline electrolytes (Fig. S10). Strikingly, the
dl
2
S9c), revealing the high exposure of catalytic edge sites in
η10 of CoMoS nanotubes is lower than most of the documented
3
hierarchical CoMoS nanotubes composed of ultrathin nanosheets.
non-noble-metal catalysts, making it a promising candidate for
3
Besides the numbers of active sites, the activity of per catalytic 115 HER electrocatalyst in alkaline solution. The corresponding Tafel
-
1
site is another crucial criterion that determines the HER
plots are displayed in Fig. 5b, with a Tafel slope of 105 mV dec .

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Journal of Materials Chemistry A
Page 6 of 8
Moreover, the long-term durability test (Fig. 5c) is also
320 mV after 10 h, showing a current retention of 88.4%. The
performed, in which the CoMoS3 delivers a relatively good 60 polarization curve obtained after long-term test (Fig. S14) shows
catalytic stability at a fixed overpotential of 135 mV, generating
stable current density for more than 10 h with small decrease
from the initial 10.8 mA cm to the final 9.7 mA cm with a
current retention of 89.8%. After 10 h, a similar polarization
a slightly depressed catalytic performance, exhibiting a η10 of 425
mV. The EDX results obtained from the catalyst after catalysis
test show that the atomic ratio of S : Co : Mo is about 61.9 : 18.6 :
19.5, indicating the good stability of CoMoS3 nanotubes.
-
2
-2
5
0
5
0
5
0
5
0
5
0
5
curve (Fig. 5d) can be retained. In comparison with the initial 65 Moreover, CoMoS3 nanotubes exhibit high FE (Fig. S15) of
cycle, a decreased η10 of 184 mV is obtained, with a fade of 51
mV on overpotential. The overpotential fade in KOH is larger
than that (26 mV) in acidic solution, which suggests that CoMoS3
exhibits junior HER stability in alkaline solution, although further
in-depth research is needed for the specific mechanism. The FE
nearly 100% for oxygen evolution in 1 M KOH.
1
1
2
2
3
3
4
4
5
5
Conclusions
In summary, we report, for the first time, the successful synthesis
for CoMoS nanotubes in KOH is also obtained (Fig. S11), in
3
70
of hierarchical MoCoS nanotubes constructed by 2D ultrathin
3
which the FE is close to 100%.
nanosheet subunits, using a self-sacrifice template method that
starts from CoMoO4 nanorods. Guaranteed by the specific
structure and synergism of ternary Co-Mo-S, our present sample
is given the opportunities to function as highly active and stable
75 catalysts for high-efficiency water electrolysis, including HER in
acidic/alkaline solution and OER in alkaline solution. In H SO ,
To better understand the enhanced catalytic performance in
alkaline solution, the double-layer capacitance (Fig. S12a) of
CoMoS3 nanotubes in KOH is also obtained, and the
corresponding Cdl (Fig. S12b) and TOF (Fig. S12c) value are
-
2
calculated. As shown in Fig. S12b, a high C of 10460 μF cm is
dl
2
4
achieved due to structural advantages of the highly exposed
active edge sites, which is equal to the value in H SO .
the CoMoS nanotubes deliver excellent HER catalytic activity,
3
2
4
with low onset overpotential of 80 mV and small η10 of 143 mV,
as well as stable catalytic performance for more than 10 h.
Additionally, the catalyst exhibits robust catalytic performance
towards both HER and OER in alkaline solution, such as low
onset overpotentials of 65 mV for HER and 1.47 V for OER, and
small overpotentials of 143 mV for HER and 320 mV for OER
Interestingly, one can see from Fig. S12c that CoMoS nanotube
3
exhibits higher TOF values in KOH than that in H SO ,
2
4
80
suggesting that CoMoS possesses high catalytic active per active
3
sites in KOH, which should be responsible for the improved
catalytic performance in alkaline solution.
-
2
to afford a current density of 10 mA cm . We believe that, the
present synthesis method may pave a way into the fabrication of
hollow and/or hierarchical metal sulfide-based architecture using
nanostructured metal oxides as precursors for energy conversion
and storage applications. The study on the HER performance of
CoMoS3 in KOH would set an example to extend the HER
applications of various metal sulfides in alkaline solution.
8
5
90
Acknowledgment
We thank for the financial support from Natural Science
Foundation (2016GGX104019, ZR2014JL015, ZR2014EMM004)
of Shandong Province.
Fig. 6 OER performance of CoMoS
3
in 1 M KOH: (a) Polarization curves
nanotubes, and RuO
2
of MoS , CoS , CoMoS nanoparticles, CoMoS
2
2
3
3
95
electrodes in 1 M KOH, (b) time-dependent current density curve under
static overpotential of 320 mV.
Notes and references
Furthermore, CoMoS is tested as the electrocatalyst for the
a
3
Key Laboratory of Rubber-plastics, Ministry of Education/Shandong
OER in alkaline solution, which exhibits good catalytic activity
Provincial Key Laboratory of Rubber-plastics, Key Laboratory of Sensor
Analysis of Tumor Marker (Ministry of Education), College of Chemistry
and Molecular Engineering, Qingdao University of Science & Technology,
Qingdao 266042, China
and durability. As is shown in Fig. 6a, CoMoS particles show
3
better catalytic performance than pristine MoS2 and CoS2,
100
indicating that doped Co could boost the catalytic activity of
MoS . It is reported that, Co species are liable to interact with
b
2
College of Science and Technology, Agricultural University of Hebei,
4
4
water molecules via the formation of Co-O bonds. This can
expedite the oxygen evolution and achieve improved OER
Cangzhou 061100, China
† Electronic Supplementary Information (ESI) available: [details of any
activity. In comparison with CoMoS3 particles, CoMoS3 105 supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
nanotubes exhibit a remarkably superior OER activity with an
onset potential of ~1.47 V and η10 of ~320 mV, assigning to the
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Journal of Materials Chemistry A
Page 8 of 8
View Article Online
DOI: 10.1039/C7TA02768K
This paper reports the hierarchical CoMoS
3
nanotubes constructed by ultrathin nanosheet subunits as
the dual-catalyst for robust electrochemical water splitting.