Solvothermal Synthesis of Mesoporous 3D-CuCo2O4 Hollow Tubes as Efficient Electrocatalysts for Methanol Electro-Oxidation

Article abstract of DOI:10.1002/cctc.201901028

Transition metal oxides have attracted attention as promising electrode materials for energy storage and conversion devices with high electrochemical activity and stability. In this study, a simple and cost-effective solvothermal synthesis of rectangular 3D CuCo₂O₄ hollow tubes have been developed for methanol electro-oxidation application. Electrochemical analysis shows that CuCo₂O₄ hollow tubes exhibit superior electrochemical performance in terms of current density and cycling stability, with 75 mA cm^?2 and 90 % retention rate after 1000 cycles, respectively. The high electrochemical performances are mainly due to the morphological structure of CuCo₂O₄ hollow tubes, which possess high surface area and porosity, resulting to a faster electron-ion transfer, enhanced reactivity and stability. Given that the synthesis of CuCo₂O₄ hollow tubes involve a facile and cost-effective technique, the present approach, thus, opens a new era to novel materials for large-scale processes in different electrochemical applications.

Full text of DOI:10.1002/cctc.201901028

Accepted Article
Title: Solvothermal Synthesis of Mesoporous 3D-CuCo2O4 Hollow
Tubes as Efficient Electrocatalysts for Methanol Electro-oxidation
Authors: Diane Clare M. Tionco, Harsharaj S. Jadhav, Animesh Roy,
and Jeong Gil Seo
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the VoR from the journal website shown below when it is published
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To be cited as: ChemCatChem 10.1002/cctc.201901028
Link to VoR: http://dx.doi.org/10.1002/cctc.201901028
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Solvothermal Synthesis of Mesoporous 3D-CuCo2O4 Hollow
Tubes as Efficient Electrocatalysts for Methanol Electro-oxidation
Diane Clare M. Tiongco,[a] Harsharaj S. Jadhav,[a] Animesh Roy,[a] and Jeong Gil Seo*[a]
Abstract: Transition metal oxides have attracted attention as
promising electrode materials for energy storage and conversion
devices with high electrochemical activity and stability. In this study,
a simple and cost-effective solvothermal synthesis of rectangular 3D
CuCo2O4 hollow tubes have been developed for methanol electro-
oxidation application. Electrochemical analysis shows that CuCo2O4
hollow tubes exhibit superior electrochemical performance in terms
of current density and cycling stability, with 75 mA cm⁻2 and 90%
retention rate after 1000 cycles, respectively. The high
electrochemical performances are mainly due to the morphological
structure of CuCo2O4 hollow tubes, which possess high surface area
and porosity, resulting to a faster electron-ion transfer, enhanced
reactivity and stability. Given that the synthesis of CuCo2O4 hollow
tubes involve a facile and cost-effective technique, the present
approach, thus, opens a new era to novel materials for large-scale
processes in different electrochemical applications.
been studied.[5,7,13] At present, platinum and ruthenium alloys
have shown superior stability and catalytic activity; however,
their degradation and limited resources have caused
hindrance for the commercialization of DMFC.[9-10]
a
Consequently, transition metal oxides, such as Co3O4,
Fe3O4, ZnO, and NiCo2O4, are currently being explored with
respect to catalytic performance and cost reduction.[7,12,14-15]
Transition metal oxides improve electrocatalytic performances
thanks to their enhanced surface area and short electron-ion-
[1,16]
transport pathways.
In particular, CuCo2O4 has been widely
used as promising electrocatalysts for Li-ion batteries and
supercapacitors due to their abundance, high theoretical
capacity, low cost, ease of preparation, and environmental
friendliness.[2,17-18] More significantly, CuCo2O4 has a higher
electrochemical performance than the single component metal
oxides, copper oxides and cobalt oxides, since addition of metal
ion affects the morphology, particle size, and surface area of the
electrocatalyst.[9,19]
In addition, nanoparticle supports for transition metal oxides
are being explored for a more stable and active catalyst. Some
of which are carbon and nitrogen-doped nanomaterials, which
enhance the morphology and conductivity of the electrocatalyst.
Carbon-based materials include reduced graphene oxide,
carbon nanotubes, and graphene, which serve as a support due
to their high surface area and conductivity.[11,20-21] On the other
hand, nitrogen doping increases the stability and conductivity of
the catalyst.[22] Other studies make use of surface capping
agents, such as PVP and decylamine, to promote uniform
nucleation, enhance thermal stability, and reduce agglomeration
of nanoparticles.[23-25] To further enhance the electrochemical
activity of bimetallic oxides, synthesis of these electrodes
through hydrothermal, solvothermal, electrochemical synthesis
is explored. However, the use of toxic solvents and high
temperature are still prominent in synthesizing an electrocatalyst.
Thus, development of simple, environment-friendly and
economical synthesis method is still being investigated.[9,26]
To date, only two reports have been conducted regarding
CuCo2O4 electrodes for methanol oxidation such as the nano-
sized CuCo2O4 spinel-type that were synthesized by co-
precipitation method, which exhibited 45 mA cm-2 at 10 mV s-1,
and the mesoporous CuCo2O4 nanograsses that were prepared
by hydrothermal approach, which has a discharge capacity of 60
mA cm-2 at 5 mV s-1.[27-28] Herein, we have reported a facile and
cost-effective solvothermal synthesis of 3D rectangular CuCo2O4
hollow tube-like structure as an electrocatalyst for methanol
Introduction
The increasing demand for clean and sustainable next-
generation energy sources has led researchers to develop
alternative energy conversion and storage devices. Among
these, the advancement of batteries, supercapacitors, and fuel
cells have emerged to address the current environmental issues
and meet the future energy requirements.[1-4] Recently, fuel cells
have attracted great attention due to their high efficiency, low
environmental gas emissions, and direct conversion of chemical
to electrical energy. In particular, direct methanol fuel cells
(DMFCs) are a promising storage system due to their high
volumetric energy density, low cost, and ease of handling and
storage of liquid fuel.[5-8] Besides hydrogen-fed fuel cells,
methanol has been considered as a favorable option due to its
safe handling and storage, high energy density, and
availability.[9-12] Despite all the advantages, commercialization of
DMFC is yet to be proven due to the problems arising from the
stability and life cycles of electrocatalysts.
Platinum, which is the most common and effective catalyst
used, exhibits higher energy conversion and catalytic activity
than other electrocatalysts, but due to its high cost and catalytic
poisoning, continuous development of noble and non-noble
based catalysts such as alloys and transition metal oxides have
[a]
D. C. M. Tiongco, Dr. H.S. Jadhav, A. Roy, Prof. J. G. Seo
Department of Energy Science and Technology
Myongji University
electrooxidation.
The
CuCo2O4
demonstrated
higher
electrochemical activity and stability as compared to the
previous research studies and to its monometallic form when
used as an electrocatalyst. The high electrochemical
performance exhibited by 3D rectangular CuCo2O4 hollow tubes
Nam-dong, Cheoin-gu, Yongin-si, Republic of Korea
E-mail: jgseo@mju.ac.kr
Supporting information for this article can be found under (via a link
at the end of the document)
thus suggests that the synthesized electrode could be
a
potential active material for methanol electro-oxidation
application.
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Results and Discussion
Physicochemical Characterization of CuCo2O4
Nanoparticles
CuCo2O4 tubes were synthesized through solvothermal process
followed by annealing in air atmosphere. TGA analysis was
carried out to determine the oxide phase formation temperature
for Cu-Co hydroxide precursors as observed in Figure S1
(supplementary information). A total weight loss for all samples
was observed around 52% in the conversion of Cu-Co precursor
to its oxide phase, CuCo2O4.
molecules present in the precursor. The second weight loss,
between 200
of Cu-Co hydroxide to CuCo2O4. Beyon
loss was observed, which indicates the complete conversion of
the reaction.[29] Thus,
atmosphere to obtain the oxide phase of the Cu-Co hydroxide
precursors.
The XRD analysis was used to determine the phase of
precursor, CuCo-3, CuCo-4, and CuCo-5; the obtained
diffraction patterns are shown in Figure 1a. XRD pattern of the
precursor shows that all peaks correspond to Cu-Co hydroxide
phase as shown in Figure S4. The samples synthesized without
PVP, CuCo-3, and CuCo-5 showed the co-existence of CuO
along with CuCo2O4, as shown in Figure 1a. On the other hand,
CuCo-4 showed pure phase of CuCo2O4 only. Absence of CuO
or other impurity peaks reveals the phase purity of CuCo-4. This
specifies that the solvothermal reaction time greatly affects the
presence of CuO in the sample. The characteristic diffraction
peaks of CuCo2O4 (JCPDS No. 01-1155) at 19.0, 31.4, 37.0,
39.0, 56.0, 59.6, orrespond to the (220), (311), (222),
(400), (422), (511), and (440) crystal planes, respectively.
FT-IR analysis was also investigated to determine the
molecular changes and to confirm the pure phase formation of
CuCo2O4 after annealing. Figure S5 shows the FT-IR spectrum
of the precursor. As shown, the absorption bands of the Cu-Co
precursor range from 500 to 1600 cm⁻1. The peaks from 500 to
700 cm⁻1 correspond to the trace amounts of metal present in
the precursor, and the peaks from 1300 to 1600 cm⁻1
correspond to the C-N and O-H bonds of PVP and alcohol,
respectively.[25-30] Consequently, Figure 1b shows the FT-IR
spectra of CuCo-3, CuCo-4, and CuCo-5. It can be seen that the
C-N and O-H groups that were dominant in the precursor
material disappeared due to the decomposition of PVP at high
temperature, and the intensity of peaks corresponds to the metal
Figure 1. (a) XRD patterns and (b) FT-IR spectra of CuCo2O4
- - - .
The composition and oxidation state of elements in
CuCo2O4 were investigated using XPS analysis (Figure 2). As
illustrated in Figure 2a, the full survey spectrum displays the
presence of Cu, Co, and O elements for CuCo-4 sample. Figure
2b-c further shows the high-resolved deconvoluted spectra of Co
2p, Cu 2p, and O 1s. From the Gaussian fitting method, Co 2p is
composed of spin orbits Co2+ and Co3+ together with two weak
satellite peaks that are attributed to the characteristic of Cu2+.[4]
The peaks at 779.65 eV and 794.95 eV are associated to Co3+,
and the peaks at 781.45 eV and 797.2 eV are associated to Co2+
species in the CuCo2O4 nanoparticle.[9] The XPS spectra of Cu
2p (Figure 2c) shows that the copper element also has two
valences of Cu2+ (Cu 2p1/2 at 953.85 eV) and Cu3+ (Cu 2p3/2 at
933.95 eV), together with two weak satellite peaks.[4,9] As for the
O1s spectra, three kinds of oxygen species are observed as
shown in Figure 2d. The high intensity peak at O1 (529.65 eV) is
attributed to the metal (Cu/Co) oxygen bond, while the fitting
oxides has significantly increased. As observed,
a more
prominent peak at 544 and 648 cm⁻1 were observed in the
CuCo2O4 samples, which are attributed to Cu2+─O2⁻ and
[31-33]
Co3+─O2⁻ stretching vibrations.
The FT-IR spectra of
CuCo-3, CuCo-4, and CuCo-5 showed only presence of two
peaks (at 544 and 648 cm⁻1), which confirms the pure phase
formation of CuCo2O4.[3,34]
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Figure 2. XPS analysis of CuCo2O4 hollow tubes (a) survey spectra, and deconvoluted spectra of (b) Co 2p, (c) Cu 2p, and (d) O 1s for CuCo-4 sample.
Figure 3. FE-SEM images of (a-c) CuCo-3, (d-f) CuCo-4, and (g-i) CuCo-5 at different magnification.
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peaks at O2 (531 eV) and O3 (532.2 eV) correspond to the
oxygen defects of small-particle metal oxide and physically
chemisorbed water molecules, respectively.[4,9,17-18]
the hollow nature of CuCo-4 with rectangular tube-like structures.
The high-resolution TEM images (Figure 4c-d) clearly show that
the hollow tube structure is composed of numerous
interconnected nanoparticles with plenty of mesopores in
between, which is beneficial for the diffusion of electrolyte during
electrochemical reaction.[11,38-41] Figure 4e illustrates the HR-
TEM image of the hollow tube with an interplanar spacing of
0.24 nm for (311) crystal plane of the CuCo2O4. In addition,
SAED patterns of CuCo-4 hollow tube as shown in Figure 4f
indicates its polycrystalline nature and all the diffractions rings
can be assigned to the structural phase of CuCo2O4, which is in
good agreement with the XRD results.
FE-SEM analyses of all synthesized samples were carried
out to determine effect of solvothermal reaction time on the
morphology of CuCo2O4 (Figure 3). FE-SEM images of the
precursor reveal the formation of solid rectangular tube-like
structure (Figure S6). CuCo-3 showed less uniform formation of
tube-like structure (Figure 3a-c). Furthermore, CuCo-4 displays
the uniform formation of tube-like structure with proliferation in
its width and length (Figure 3d-f). When the reaction time was
increased to 5h, the original shape of tube-like structure gets
destroyed as shown in Figure 3g-i. This indicates that the
The specific surface area serves as a determining factor for
reaction time is an important parameter in determining the shape, reaching high performance in electrochemical application.[4,41]
size and morphology of the final product. On the other hand, the
CuCo2O4 sample prepared without PVP and refluxed for 4 h
showed an irregular shape with a bunch of agglomerated
particles (Figure S7). Addition of PVP also affects the size,
distribution and dispersion of CuCo2O4 particles, and reduces
the agglomeration of the metal oxide during the synthesis
process.[35-37] Energy-dispersive X-ray (EDX) spectroscopic
analysis and elemental colour mapping of all samples were
carried out as displayed in Figure S8. Elemental colour mapping
showed uniform distribution of Cu, Co and O within the obtained
structure. Furthermore, EDX analysis reveals the weight
percentage ratio of Cu/Co, which was consistent with the
designed ratio in the precursor solution.
BET analysis, as shown in Figure S10, was performed to
determine the specific surface area of the electrode materials.
As observed, the adsorption-desorption isotherm for CuCo2O4
synthesized for 3, 4, and 5 h display a type IV isotherm with type
H3 hysteresis loop.[42] The CuCo2O4 exhibits a surface area of
12.4, 22.2, and 8.4 m2 g⁻1 for CuCo-3, CuCo-4, and CuCo-5
samples, respectively. CuCo-4 exhibits two times higher specific
surface area than the monometallic Co3O4. This indicates that
introduction of another metal ion into Co3O4 structure can
increase the specific surface area and consequently higher
number of active sites will be available for electrochemical
reaction.[3] Furthermore, insets of Figure S10 showed the BJH
pore size distribution of respective samples. CuCo2O4 sample
with the highest specific surface area possesses a pore size
distribution between 10-40 nm. The higher specific surface area
and mesoporous pore size distribution of CuCo2O4 can thus
result in higher electrochemical performance for methanol
oxidation, as compared to that of Co3O4 electrode. [33]
The hollow nature and structure of CuCo-4 tubes were
investigated by TEM, HR-TEM, and selected area electron
diffraction (SAED) analysis as shown in Figure 4. Compared to
the broken and irregular solid structure of CuCo2O4 without PVP
(Figure S9), the low-resolution TEM images (Figure 4a-b) reveal
Figure 4. (a-d) Low and high magnified TEM images, (e) HR-TEM image and (f) SAED pattern of the CuCo-4 hollow tube.
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Electrochemical Analysis of CuCo2O4
5b, the onset potential of CuO, Co3O4 and CuCo2O4 electrodes
range from 0.3 to 0.35V, respectively. The obtained onset
potential in the present study is smaller as compared to the
previously reported oxide-based electrocatalysts for methanol
oxidation.[44-47] Therefore, the higher current density and lower
onset potential of CuCo-4 electrode exhibits its superior
electrochemical performance towards methanol oxidation.
Furthermore, due to the complex nature of the reactions
involved in electrooxidation, the exact electrochemical behavior
of copper and cobalt oxides needs to be further investigated.
The possible mechanism from the cathodic potentials, CoOOH
and CuOH may form at the outer surface of the CuCo2O4
electrode as described in the following equation:
Cyclic voltammetry (CV), chronoamperometry (CA), and
electrochemical impedance spectroscopy (EIS) techniques were
used to investigate the electrochemical performance of CuCo2O4.
The electrochemical performance of CuO, Co3O4 and CuCo2O4
electrodes were investigated in a three-electrode configuration
using 1 M KOH with and without 0.5 M methanol as the
electrolyte at a scan rate of 10 mV s⁻1. The catalytic activity of
bare Ni foam was also tested to reveal its negligible current
density in comparison with other electrodes towards methanol
oxidation (Figure 5). As shown in Figure 5a and Figure S11a,
the area under the CV curves of monometallic CuO and Co3O4
electrodes are smaller than the CuCo2O4 samples reacted for 3,
4 and 5 h. Higher area under the curve of all the CuCo2O4
electrodes indicates a higher electrochemical activity than that of
CuO and Co3O4 electrodes.[43] Also, as illustrated in Figure 5a,
CuCo-4 has the largest enclosed area, which confirms that it has
the highest electrochemical activity among the other CuCo2O4
electrodes. Furthermore, the reduction and oxidation peaks
present in the working electrode correspond to the faradic redox
reaction involving Cu2+/Cu+ and Co3+/Co2+ paired with OH⁻
ions.[1,43]
In addition, Figure 5b and Figure S11b show the CV curves
of CuO, Co3O4 and CuCo2O4 electrodes in 1M KOH electrolyte
with 0.5 M methanol addition within the potential window of
− 1 ⁻1. Addition of methanol
significantly increased the anodic current density of all
electrodes. Among all tested electrodes, monometallic CuO and
Co3O4 exhibited the lowest current densities of 24 mA cm⁻2 and
35 mA cm⁻2, respectively, while CuCo-4 showed the highest
current density of 75 mA cm⁻2. The increased current density of
CuCo-4 electrode is almost 3.5-fold higher than that of CuO and
2-fold higher than Co3O4, which is mainly attributed to the co-
existence of Co and Cu elements. The addition of Cu ion
improves the overall characteristic of the CuCo-4 electrode in
terms of surface area, porosity, ion-electron transport, and
electrochemical activity.[4,9,43] Besides current density, the onset
potential is another key factor in determining the performance of
electrocatalysts in methanol oxidation.[9] As observed in Figure
(1)
(2)
(3)
As defined in equation (1), the catalyst reacts with the reactant
that leads to a forward shift to the reaction. Afterwards, the
resulting intermediate species are converted to their products as
shown in equations (2) and (3). Furthermore, reaction of OH⁻
species with copper intermediates are highly favored than with
cobalt intermediates since the latter reaction has the tendency to
form other products that could dissolve water, which then
causes intermediate poisoning that could interfere in the
electrochemical reaction.[1,9]
Chronoamperometry (CA) test was carried out to study the
electrochemical activity and stability of all electrodes. This
method measures the current-time dependence of the electrode
in a diffusion-controlled medium.[48-51] As shown in Figure 6a and
Figure S12, CA test of bare Ni foam, CuCo2O4 electrodes
synthesized with and without PVP, CuO and Co3O4 were carried
out at 0.5 V (vs. SCE) for 2500 seconds. Negligible current from
bare Ni foam in CA test further reveals its inactivity towards
methanol oxidation. CA test clearly shows that among all
electrodes, CuCo-4 exhibits a higher current density with 100%
retention rate even after 2500 seconds.
Figure 5. Cyclic voltammograms of CuCo2O4 (without PVP), CuCo-3, CuCo-4, and CuCo-5 in (a) 1M KOH and (b) 1 M KOH and 0.5 M methanol.
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Along with the higher current density and low onset
potential of any electrocatalyst, its long-term stability is also
crucial. As shown in Figure 6b and Figure S13, the long-term
stability and efficiency of the synthesized samples with and
without PVP were confirmed by using CV test at a scan rate of
10 mV s-1 for 1000 cycles. Among all the cycling tests, CuCo-4
exhibited the highest current density before and after 1000
cycles, and even after replacing the solution with a new
electrolyte. Initially, after the first cycle, CuCo-4 electrode
reflects the current density of 75 mA cm-2, and after 1000 cycles,
it decreased to a current density of 60 mA cm-2. After replacing
with a new electrolyte, 90% of the original current density value
was retained, which shows that the decrease in current density
was due to the consumption of methanol during the cycling
test.[4,9] Due to the long-term stability and high specific surface
area of CuCo-4 hollow tubes, it has shown higher
electrochemical performance towards methanol oxidation as
compared to plenty earlier reports summarized in Table S1.[7,9,27-
electrocatalyst when subjected to cycling test as shown in Figure
6c. No particular change was observed even after 1000 cycles.
This further confirms the structural and morphological stability of
the sample even after long-term stability test.
EIS analysis was carried out before and after the cycling
stability of CuCo-4 electrode to determine the charge transfer
resistance, which could affect the electrocatalytic activity and
stability of the electrode. Figure 6d shows the Nyquist plots
recorded in 1 M KOH with 0.5 M methanol with an amplitude of
1 v q 1 MHz − 1 Hz B N q
plots showed depressed semi-circle in a high frequency, which
is related to the charge transfer resistance between the
electrolyte and the active material, and a low frequency line,
which is related to the redox capacitance behavior of the
electrode.[47,55-56] In addition, as shown in Figure 6d, the initial
Ω Ω 1
cycles. This could be attributed to the adsorption of methanol or
oxidation of intermediates in the electrode, which then leads to a
decrease in the current density. However, since there was no
obvious change in the diameter of the semicircle, the CuCo-4
electrode has a high tolerance to intermediate poisoning. In
addition, a small amount of charge transfer resistance means a
fast electron transfer in the electrode and at the electrode-
electrolyte interface, which then indicates that the electrode has
good stability.[3,7]
28,45-46,52-54]
For instance, nano-sized CuCo2O4 spinel-type,
synthesized by co-precipitation method, exhibited 45 mA cm-2 at
10 mV s-1.[53] Mesoporous CuCo2O4 nanograsses synthesized on
copper foam through hydrothermal approach obtained 60 mA
cm-2 at 5 mV s-1.[54] In the present study, novel synthesis of
CuCo-4 electrocatalyst by solvothermal method achieved 75 mA
cm-2 at 10 mV s-1. FE-SEM analysis of the electrode was also
carried out to investigate the morphological change of the
Figure 6. (a) Chronoamperometry test of CuCo-4 hollow tubes in comparison with CuCo2O4 (without PVP), CuCo-3 and CuCo-5, (b) cycling stability of CuCo-4
using CV, (c) FE-SEM image of CuCo-4 after the cycling test and (d) Nyquist plot of CuCo-4 before and after cycling test.
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surface area and pore size distribution of the CuCo2O4 sample were all
studied using a Belsorp mini-II (BEL, Japan) with a Brunauer-Emmett-
Teller (BET) method.
Conclusions
In conclusion, we have demonstrated synthesis of CuCo2O4
hollow tubes through a facile, cost effective solvothermal method
followed by calcination and evaluated for methanol
electrooxidation. Compared to its monometallic form, CuCo2O4
hollow tubes exhibited excellent electrocatalytic activity for
methanol electrooxidation with a current density of 75 mA cm⁻2
and a retention rate of 90% after 1000 cycles. The high
electrochemical performance of the CuCo2O4 hollow tubes could
be attributed to the presence of copper ions and higher specific
surface area with abundant active sites material. Thus, the
present study suggests that the morphology of electrocatalyst
can play a crucial role in determining its electrochemical
performance for methanol oxidation. Furthermore, the present
synthesis approach can offer diverse opportunities for design
and synthesis of several oxide-based materials for energy
storage and conversion applications.
Electrochemical measurements
The electrochemical properties of CuCo2O4 electrode for methanol
oxidation
were
determined
by
cyclic
voltammetry
(CV),
chronoamperometry (CA), and electrochemical impedance spectroscopy
(EIS) using a three-e - -
electrode cell system in aqueous 1M KOH electrolyte, with and without
0.5 M methanol, consisted of CuCo2O4 as a working electrode, a
platinum mesh as a counter electrode, and a saturated calomel electrode
(SCE) as a reference electrode. CV measurements were done at a scan
rate of 10 mV s-1, chronoamperometry at a potential of 500 mV, and EIS
analysis with an amplitude of 10 mV over the frequency range of 1 MHz-
1 Hz.
For the working electrode preparation, 4 mg of the active material was
μL NM 1 μL N -sonification for 5
1 μL k N
0.5cm X 0.5cm area an v .
Experimental Section
Materials
Acknowledgements
Copper (II) acetate monohydrate (CuAc, 99.0% assay, Sigma-Aldrich),
cobalt (II) acetate tetrahydrate (CoAc, 99.0% assay, Sigma-Aldrich), and
polyvinylpyrrolidone (PVP, MW=10000, Sigma-Aldrich) were utilized as
precursors without any further purification. Ethanol (anhydrous, 99.9%)
was purchased from Daejung chemicals.
This work was supported by Nano-Material Fundamental
Technology Development (2016M3A7B4909370) through the
National Research Foundation of Korea (NRF) funded by the
Ministry of Science, ICT, and Future Planning. This work was
supported by the Energy Efficiency
& Resources (No.
20163010092210) of the Korea Institute of Energy Technology
Evaluation and Planning (KETEP) grant funded by the Korea
government Ministry of Trade, Industry & Energy.
Synthesis of CuCo2O4
Initially, 0.67 g of CuAc, 1.66 g of CoAc, and 6.0 g of PVP were dissolved
in 200 mL of ethanol under magnetic stirring for 30 min to obtain a
homogeneous solution. The resulting mixture was heate
v
v
v v -
⁻1 to obtain
CuCo2O4 hollow tubes. One sample was prepared without PVP and was
synthesized for 4 h in comparison to other samples. CuO and Co3O4
samples were also synthesized with a similar process using precursors
containing only CoAc and CuAc, respectively, as control samples.
CuCo2O4 z v
were named as CuCo-3, CuCo-4,
and CuCo-5, respectively, in further discussion.
Keywords: Metal oxides • Hollow tubes • Electrocatalyst •
Methanol oxidation • CuCo2O4
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diffraction (XRD, Rigaku, D/max- Kα ˚
performed to determine the phase and purity of the sample. Fourier
transform infrared spectra (FT-IR) were recorded on an Agilent, Cary 630
FT-IR spectrometer in the range of 450 to 4000 cm⁻1. The surface
morphology and elemental distribution were analyzed by field emission
scanning electron microscopy (FE-SEM, Hitachi S4800) and X-ray
spectrometer (EDS), respectively. Transmission electron microscopy
(TEM, JEOL JEM-200CX) was carried out to determine the hollow nature
and structure of calcined sample. The oxidation states of elements and
its composition in CuCo2O4 sample were analyzed using X-ray
photoelectron spectroscopy (XPS Thermo, ESCALAB-MKII). The specific
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Entry for the Table of Contents
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CuCo2O4 hollow tubes serve as
superior electrocatalysts for
methanol electro-oxidation
Diane Clare M. Tiongco, Harsharaj S.
Jadhav, Animesh Roy, and Jeong Gil
Seo*
Page No. – Page No.
Solvothermal Synthesis of
Mesoporous 3D-CuCo2O4 Hollow
Tubes as Efficient Electrocatalysts
for Methanol Electro-oxidation
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