Decoration of copper foam with Ni nanorods and copper oxide nanosheets to produce a high-stability electrocatalyst for the reduction of CO2: Characterization of the electrosynthesis of isonicotinic acid

Article abstract of DOI:10.1016/j.crci.2019.09.007

CuO–Cu₂O (Cu_xO) nanosheets were coated on a copper foam substrate by the electrochemical anodization method in an alkaline solution. Constant current coulometry was performed to electrodeposit Ni nanorods on the surface of a Cu/Cu_xO electrode. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) proved that the copper oxide nanosheets were anchored on the copper foam substrate and modified by Ni nanorods (Cu/Cu_xO/Ni). The process took place via a facile and inexpensive electrodeposition method. As the results indicate, owing to the synergistic effect of adjacent Cu_xO and Ni sites, a Cu/Cu_xO/Ni electrode has a very good and stable electrocatalytic activity to reduce CO₂. As tested in this study, the product of the electrocatalytic reduction of CO₂ (i.e. activated CO₂, or CO₂ ^??) can be used for the electrocarboxylation of pyridine in mild conditions. Once an electron is transferred from CO₂ ^?? to pyridine, a pyridine radical anion is formed. Based on the EC'C′CC mechanism, this radical anion reacts with CO₂ ^?? and produces isonicotinic acid as the main product. In addition, two pyridine radical anions react together and produce a 4,4′-bipyridine dimer. The high stability of the electrocatalyst during the electrolysis process and the simplicity of the workup make the proposed modified electrode appropriate for the electrosynthesis of some organic compounds.

Full text of DOI:10.1016/j.crci.2019.09.007

C. R. Chimie xxx (xxxx) xxx
Contents lists available at ScienceDirect
Comptes Rendus Chimie
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Full paper/M eꢀ moire
Decoration of copper foam with Ni nanorods and copper
oxide nanosheets to produce a high-stability electrocatalyst
for the reduction of CO : Characterization of the
2
electrosynthesis of isonicotinic acid
*
Safoora Mohammadzadeh, Hamid R. Zare , Hossein Khoshro
Department of Chemistry, Faculty of Science, Yazd University, Yazd, 89195-741, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
CuOeCu O (Cu O) nanosheets were coated on a copper foam substrate by the electro-
2
x
Received 13 July 2019
Accepted 23 September 2019
Available online xxxx
chemical anodization method in an alkaline solution. Constant current coulometry was
performed to electrodeposit Ni nanorods on the surface of a Cu/Cu O electrode. Scanning
electron microscopy (SEM) and X-ray diffraction (XRD) proved that the copper oxide
x
nanosheets were anchored on the copper foam substrate and modified by Ni nanorods
Keywords:
(
Cu/Cu
method. As the results indicate, owing to the synergistic effect of adjacent Cu
sites, a Cu/Cu O/Ni electrode has a very good and stable electrocatalytic activity to reduce
x
O/Ni). The process took place via a facile and inexpensive electrodeposition
Cu foam
x
O and Ni
CuOeCu
Ni nanorods
Cu/Cu O/Ni electrocatalyst
CO electroreduction
2
O nanosheets
x
CO
2
. As tested in this study, the product of the electrocatalytic reduction of CO
2
(i.e.
x
ꢀꢁ
activated CO
ditions. Once an electron is transferred from CO
formed. Based on the EC'C CC mechanism, this radical anion reacts with CO
2
, or CO
2
) can be used for the electrocarboxylation of pyridine in mild con-
2
ꢀꢁ
2
to pyridine, a pyridine radical anion is
0
ꢀꢁ
2
and produces
isonicotinic acid as the main product. In addition, two pyridine radical anions react
0
together and produce a 4,4 -bipyridine dimer. The high stability of the electrocatalyst
during the electrolysis process and the simplicity of the workup make the proposed
modified electrode appropriate for the electrosynthesis of some organic compounds.
©
2019 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1
. Introduction
reported to activate CO
The electrocatalytic reduction of CO
ways to activate it in mild conditions (i.e. room tempera-
ture and pressure) [12]. However, CO reduction at the
surface of an ordinary electrode requires high over-
potentials. Therefore, a range of electron transfer mediators
(catalysts) such as metal complexes [7,13] and organic
compounds [3,14] have been used for the electrocatalytic
2
and convert it into radical anions.
2
is one of the easiest
Continuous emission of carbon dioxide (CO
dustrial activities has caused serious global warming and
climatic challenges [1e5]. Therefore, the conversion of CO
into useful organic compounds is of great interest and
importance [6,7]. CO is a stable compound, and the ki-
netics of its conversion into a radical anion (activated CO
2
) from in-
2
2
2
2
)
is very slow [8]. Several methods, such as chemical reduc-
tion [9], photochemical reduction [2], biological reduction
2
reduction of CO at low overpotentials. Most of the pro-
posed catalysts suffer from certain problems, such as
difficult and expensive synthesis, deactivation during the
electrocatalytic process, and workup complexity in the
[
10,11], and electrochemical reduction [4], have been
reduction of CO
electrosynthesis of organic compounds. In the literature,
2 2
and the use of activated CO for the
*
Corresponding author.
E-mail address: hrzare@yazd.ac.ir (H.R. Zare).
https://doi.org/10.1016/j.crci.2019.09.007
631-0748/© 2019 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
Comptes Rendus Chimie, https://doi.org/10.1016/j.crci.2019.09.007
2

2
S. Mohammadzadeh et al. / C. R. Chimie xxx (xxxx) xxx
there are reports on the application of Cu, Ni, Sn, Pt, Zn, Pb,
and Ti electrodes, as well as various oxidized forms of these
metals, for the electrochemical reduction of CO [3,15e24].
2
Among the transition metals and their oxides, copper and
copper oxides are widely used as electrode materials for
x x
containing Ni, Cu/Cu O, and Cu/Cu O/Ni electrodes as the
working electrodes, Ag/AgCl/KCl (sat'd) as the reference
electrode, and a Pt wire as the counter electrode. Controlled
potential coulometry (CPC) and constant current coulom-
etry (CCC) were performed using a SAMA 500 electro-
the electrochemical reduction of CO
abundance, low cost, and relatively good chemical stability
of these materials [3,25]. Despite these advantages, copper
2
. This is owing to the
x
analyzer system in an undivided glass cell with a Cu/Cu O/
2
Ni electrode as the cathode, a platinum plate (ca. 6 cm ) as
the counter electrode, and Ag/AgCl/KCl (sat'd) as the
reference electrode.
2
electrodes rapidly lose their activity for CO reduction [26].
Copper oxides with crystalline structures [20,27] and
different morphologies, however, have very good electro-
catalytic activity [25,28].
Nickel is applied in micromechanical devices, data
storage, magnetic sensors, catalyst manufacturing, and
X-ray powder diffraction (XRD) patterns were taken in
the reflection mode of Cu K
a
(
l
¼ 1.5406 Å) radiation in a 2
q
ꢂ
ꢂ
range from 30 to 80 on a senware AW-DX300 X-ray
diffractometer. The surface morphologies of the coatings
were studied by scanning electron microscopy (SEM)
(TESCAN, Vega3, and Czech).
2
protection against corrosion [29]. For CO reduction, Ni
electrodes show less electrocatalytic activity than copper
electrodes [30]. The electrocatalytic activity of Ni for the
x
2.2. Preparation of a Cu/Cu O nanosheets electrode
2
reduction of CO can be improved by using electrodes made
of Ni composites or Ni alloys [21,30e32]. For example, Hori
et al. used a Ni-modified copper electrode for the electro-
reduction of CO [27].
2
CuOeCu O (Cu O) nanosheets were coated on a copper
2
x
2
foam (0.25 cm ) by an electrochemical anodization method
in an alkaline solution [3]. Briefly, a piece of Cu foam was
first cleaned in a 1.0 M HCl solution to remove any oxide
layer on it. Then, the electrode was rinsed with water and
dried up under Ar steam. The copper foam, as the working
electrode, was immersed into a 3.0 M KOH aqueous solu-
There are reports on the use of carbon dioxide to pro-
mote the reduction of organic compounds [33,34]. As an
ꢀꢁ
example, activated CO (CO ) reduces pyridine, and iso-
2 2
nicotinic acid is finally formed as a major product [29].
Isonicotinic acid synthesis is significant because of its
participation in the synthesis of some pharmaceutically
important drugs such as isoniazid, terfenadine, and nial-
amide [35,36]. It also plays important roles as a plant
growth regulator (inabenfide), a photosensitive resin sta-
bilizer, an electroplating additive, and an anticorrosion re-
agent [37].
ꢂ
tion at 40 C, and the anodization process was carried out at
ꢁ2
a current density of 30 mA cm for 20 min. In addition, a
platinum (Pt) plate was used as the counter electrode.
Finally, the dark black film fabricated on the copper foam
was rinsed with deionized water and ethanol and dried in
ꢂ
an electrical oven at 60 C for 2 h.
In the present research, copper oxide nanosheets were
anchored on a copper foam and modified by Ni nanorods
via a facile and inexpensive electrodeposition method. The
copper foam was used as a substrate to provide a large
surface area for the growth of copper oxide nanosheets on
x
2.3. Preparation of a Cu/Cu O/Ni nanorods electrode
Ni was coated on a Cu/Cu
Watts-type bath [38,39]. The bath contained nickel sulfate
(NiSO $6H O, 0.10 M), nickel chloride (NiCl $6H O, 0.02 M),
a critical micelle concentration (CMC) of sodium dodecyl
x
O foam substrate using a
4
2
4
2
its 3D frame. Then, the modified electrode (Cu/Cu
was used for CO reduction. Finally, isonicotinic acid was
synthesized by the reaction of pyridine with activated CO
x
O/Ni)
ꢁ1
2
sulfate (SDS, 0.06 g L ) as a surfactant, and the complexing
agent of trisodium citrate (Na , 0.50 M). Citric acid
was added to the electrodeposition bath solution, and pH
was adjusted to 4.5. The Cu/Cu O electrode, as a cathode,
2
.
3 6 5 7
C H O
ꢀꢁ
2 2
, CO , has two roles
The results indicate that activated CO
in the electrosynthesis of isonicotinic acid. At first, CO
transfers one electron to pyridine and forms a pyridine
ꢀ
ꢁ
2
x
and the platinum plate, as an anode, were immersed into
the bath for Ni nanorod electrodeposition. The solution was
stirred moderately using a magnetic stirrer during the
electrodeposition process. The CCC method was used to
ꢀ
ꢁ
to form
radical anion. Then, this anion reacts with CO
isonicotinic acid in the presence of air [29].
2
2
. Experimental setup
.1. Chemicals and instruments
Tetrabutylammonium perchlorate (TBAP) (>98.0%),
electrodeposit the Ni nanorods on the Cu/Cu
surface.
x
O electrode
2
2.4. Electrolysis of pyridine in the presence of CO
2
at the Cu/
x
Cu O/Ni electrode surface
acetonitrile (ACN), potassium hydroxide (KOH), and pyri-
dine (99.8%) were purchased from Merck Company and
used without any further purification. Argon (Ar), carbon
The CPC method was used to run the process of pyridine
electrolysis in 50.0 mL of ACN containing 0.1 M TBAP and
1.0 mmol of pyridine. Before every experiment, the solution
dioxide (CO
purity of 99.99% and the thickness of 2 mm), and Ni foam
with the purity of 99.99% and the thickness of 1.5 mm)
2
) with the purity of 99.995%, Cu foam (with the
was bubbled with Ar gas for 10 min. CO
into the solution during the electrolysis, and a constant
potential of ꢁ1.5 V was applied to the Cu/Cu O/Ni working
electrode. The results showed that pyridine conversion was
2
was also bubbled
(
were also used.
x
Linear sweep voltammetry was carried out using an
EG&G PARSTAT 2273 equipped with the Power Suite soft-
ware in a conventional three-electrode electrochemical cell
ꢁ1
about 100% after 3.0 F mol of the starting compound
(pyridine) was spent at room temperature. After the
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
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3
electrolysis, the solvent was evaporated completely, and
the residue was dissolved in diethyl ether and filtered (5 ꢃ
0 mL). As the ether evaporated, the product was identified
2
1
13
by Fourier-transform infrared (FTIR), H, and C nuclear
magnetic resonance (NMR) spectroscopies. The spectral
characteristics of the products were determined as follows
(
see Figs. S1eS6 of the Supplementary Information): iso-
1
nicotinic acid: H NMR (CDCl
.2),
7.66 (d.d, 2H, j ¼ 3.2),
CDCl , 100.6 MHz): 128.72, 130.83, 132.41, 167.63 ppm,
IR: 3379 cm (OeH), 1714, 1665 (C¼O), 1590 (C¼C), 1095
3
, 400 MHz):
d
7.47 (d.d, 2H, j ¼
13
3
(
d
d
7.95 (s, 1H, CO
2
H), C NMR
3
d
ꢁ1
0
1
1
(
3
C-O),; 4,4 - bipyridine: H NMR (CDCl , 400 MHz): H
13
NMR: 7.48 (d, 4H, j ¼ 6), 8.68 (d, 4H, j ¼ 5), C NMR (CDCl
3
,
1
1
00.6 MHz): 121.44, 145.57, 150.67 ppm; FT-IR: 1696,
d
ꢁ1
ꢁ1
653 cm (C¼N), 1578, 1555 cm (C¼C), 1453, 1248, 1085,
ꢁ
1
and 756 cm
.
3
. Results and discussion
Fig. 2. The SEM image of the framework of Cu foam electrode. SEM, scan-
ning electron microscopy.
3
.1. Characterization
x
Fig. 1 displays the XRD pattern of the (A) Cu/Cu O and
(
B) Cu/Cu
crystallographic parameters obtained from the XRD data of
the Cu/Cu O and Cu/Cu O/Ni electrodes are in accordance
with the crystallographic planes of Cu (JCPDS No. 00-004-
836), CuO (JCPDS No. 00-045-0937), and Cu O (JCPDS No.
1-074-1230). In addition, as it can be seen in the XRD
pattern, there exist three broad peaks (signed as *) for the
Cu/Cu O/Ni electrode in a position between the peaks of
pure Cu (JCPDS No. 00-004-0366) and Ni (JCPDS No. 00-
01-1258). These broad peaks have more prominence and
x
O/Ni electrodes. As the figure suggests, the
in the diffraction peaks. In addition, the reduction of the
oxidized forms of copper along with Ni ions must have
x
x
increased the peak intensity of Cu. The diffraction peak at
ꢂ
0
0
2
the 2
q
angle of 37.6 is probably related to the nickel oxide
(JCPDS No. 00-047-1049).
To study the surface morphology of the Cu foam, Cu/
x x
Cu O, and Cu/Cu O/Ni, SEM micrographs were taken. As
Fig. 2 shows, the Cu foam has a three-dimensional (3D)
interconnected microporous structure with a smooth sur-
face. Fig. 3AeD show the SEM micrographs with different
x
0
less shift than the copper peaks. The explanation for this
result is that the CueNi alloy could possibly be formed by
the substitution of Cu with Ni [40], and little shifts occurred
magnifications of the CuOeCu
2
O nanosheets obtained by
anodization. As it can be seen, after anodization in air, the
2 x 2 x
Fig. 1. XRD pattern of the (A) Cu/CuOeCu O (Cu/Cu O) and (B) Cu/CuOeCu O/Ni (Cu/Cu O/Ni) foam electrodes. XRD, X-ray diffraction.
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
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S. Mohammadzadeh et al. / C. R. Chimie xxx (xxxx) xxx
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Fig. 3. (A)e(D) The SEM images of Cu/CuOeCu O nanosheets with different magnification. SEM, scanning electron microscopy.
surface of the Cu framework was covered by a dense array
of uniform, straight, and long nanosheets. In addition, the
electrode surface morphology showed that the nanosheet
clusters on the Cu foam skeleton formed flower-like
nanostructures (Fig. 3D). The SEM micrographs (with
different magnifications) of the Ni nanorods electro-
show the voltammetric responses of the same electrodes in
a solution containing CO . A comparison of the voltam-
mograms in the absence (voltammograms (a) and (b)) and
the presence of CO (voltammograms (c) and (d)) showed
that the cathodic currents increased in the presence of CO
This result indicates that both electrodes are electro-
2
2
2
.
ꢀꢁ
deposited at the Cu
x
O nanosheets surface are presented in
catalytically active for the reduction of CO
2
to CO
2
based
0
Fig. 4AeD. It can be seen that the Ni nanorods have grown
on an EC mechanism [41]. To investigate the simultaneous
in a random orientation.
effect of the electrocatalytic activity of Ni and Cu/Cu
linear sweep voltammetry (voltammogram e) was carried
out to check the CO electrocatalytic reduction at the sur-
face of the Ni nanorodsemodified Cu/Cu O (Cu/Cu O/Ni)
electrode. The results indicate that a Cu/Cu O/Ni electrode
has better electrocatalytic activity to reduce CO than a Ni
electrode or a Cu/Cu O electrode alone. The high electro-
catalytic performance of the Cu/Cu O/Ni electrode is
probably due to the synergistic effect of the adjacent Cu
and the Ni sites of this proposed modified electrode [42].
Voltammograms (e) to (h) correspond to the Cu/Cu O/Ni
electrodes after the deposition of Ni nanorods on a Cu/Cu
electrode for different times of 600, 1200, 1500, and 1800 s
in the presence of CO . As it can be seen, an increase in the
x
O,
3
.2. Electrochemical activation of CO
2
by the Cu/Cu
x
O/Ni
2
electrode and its application in the electrosynthesis of
isonicotinic acid
x
x
x
2
The electrocatalytic activity of the Ni, Cu/Cu
x
O, and Cu/
x
Cu
x
O/Ni electrodes for CO reduction was evaluated. Fig. 5
2
x
shows the linear sweep voltammograms of these elec-
trodes in an ACN solution (0.10 M TBAP) in a potential range
from ꢁ0.46 to ꢁ2.0 V. Voltammograms (a) and (b) of Fig. 5
x
O
x
show the voltammetric responses of the Ni and Cu/Cu
x
O
x
O
electrodes in an ACN solution after being bubbled with Ar
gas for 10 min, respectively. Voltammograms (c) and (d)
2
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
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Fig. 4. (A)e(D) The SEM images of Ni nanorods electrodeposited at the Cu
x
O nanosheets surface (Cu/CuOeCu
2
O/Ni) with different magnification. SEM, scanning
electron microscopy.
time of Ni nanorods deposition on the Cu/Cu
surface to 1200 s improved the electrocatalytic activity of
the modified electrode for the reduction of CO . The
decrease in the catalytic current at a higher Ni deposition
time to 1800 s was probably due to the increase in the
x
O electrode
there was no interaction between pyridine and the modi-
fied electrode. The direct reduction of CO on bare glassy
2
2
carbon electrode occurs at potentials more negative than
ꢁ2.0 V vs saturated calomel electrode (SCE) in most sol-
vents [43]. As already mentioned, the increase in the cur-
rent response of voltammogram (c), compared with
voltammogram (a), was due to the electrocatalytic reduc-
thickness of the Ni layer on the Cu/Cu
x
O surface. In other
words, the higher the deposition time, the fewer the Cu
x
O
sites exist adjacent to Ni sites, and the weaker the syner-
gistic effect of these sites.
tion of CO
took place according to Eqs. 1 and 2:
2 x
at the Cu/Cu O/Ni electrode (Cat). The reduction
To continue, the use of the CO
2
product obtained
, or
) was investigated for the electrocarboxylation of
pyridine in mild conditions. Fig. 6 shows the voltammetric
responses of the Cu/Cu O/Ni electrode in a solution after
bubbling Ar in it (voltammogram (a)). The solution con-
tained pyridine (voltammogram (b)) and CO (voltammo-
through electrocatalytic reduction (i.e. activated CO
2
ꢁ
ꢁ
ꢀꢁ
2
Cat þ e /Cat
E
(1)
CO
x
ꢁ
ꢀꢁ
/Cat þ CO2
0
Cat þ CO
2
C
(2)
2
gram (c)) in a potential range from ꢁ0.46 to ꢁ2.0 V. As
shown, the voltammogram of the electrode remained un-
changed after the addition of pyridine, which indicates that
the reduction of pyridine would not take place even by
applying the potential of ꢁ2.0 V. It is also indicated that
Voltammogram (d) belongs to the Cu/Cu
lution containing 1.0 mM of pyridine in the presence of CO .
2
x
O/Ni in a so-
As reported in the literature [33], electrocatalytic activated
ꢀꢁ
CO
2
(CO
2
) transfers an electron to the aromatic ring of
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
Comptes Rendus Chimie, https://doi.org/10.1016/j.crci.2019.09.007
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S. Mohammadzadeh et al. / C. R. Chimie xxx (xxxx) xxx
Fig. 5. Linear sweep voltammograms of the (a) Ni electrode and (b) Cu/Cu
CO , (d) as (b) after addition of CO , (e) to (h) as (d) after deposition of Ni nanorods at the Cu/Cu
800 s, respectively. Scan rate: 0.1 V s . ACN, acetonitrile; TBAP, tetrabutylammonium perchlorate.
x
O electrode in ACN (0.1 M TBAP) solution after removing O
2
, (c) as (a) after addition of
2
2
x
O electrode surface for different times of 600, 1200, 1500 and
ꢁ
1
1
Fig. 6. Linear-sweep voltammograms of Cu/Cu
x 2
O/Ni electrode in ACN (0.1 M TBAP) solution after (a) removing O , (b) addition of 1.0 mM pyridine, (c) addition of
ꢁ
1
CO and (d) as (b) after addition of CO . Scan rate: 0.1 V s . ACN, acetonitrile; TBAP, tetrabutylammonium perchlorate.
2
2
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
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Fig. 7. Controlled potential coulometry of pyridine in the presence of CO
2
at the Cu/Cu
x
O/Ni electrode surface over a period of 10 h. Potential step: ꢁ1.5 V.
pyridine, leading to a radical anion of pyridine (Eq. 3) and
the produced CO returns to the electrocatalytic cycle.
2
ꢀ
ꢁ
2ꢁ
2
Py /PyePy
ðCÞ
(6)
Py þ COꢀꢁ/Py þ CO
ꢀꢁ
ðC0Þ
(3)
2
2
þ
ꢁ
ꢁ
2H
PyePy2 / PyePy ðCÞ
(7)
A comparison of voltammograms (c) and (d) shows the
electrocatalytic current decreases inthe presence ofpyridine.
Based on this explanation, the electrochemical mecha-
nism of 4,4 -bipyridine is the same as thatof isonicotinic acid.
To determine the main product of the reaction and to
understand the mechanism of the pyridine radical anion re-
action, controlled potential coulometry was performed at
0
ꢀꢁ
2
do not participate in the elec-
This suggests that some CO
trocatalytic reduction of pyridine (Eq. 3) but react with Py
Eq. 4).
The produced pyridine radical anions can participate in
two reactions as follows. Pyridine radical anions react with
ꢀ
ꢁ
(
ꢁ
1.50 V in a solution containing CO
Cu O/Ni electrode, as described in section 3. Then, the
coulometric products were separated and characterized by
2
and pyridine at the Cu/
ꢀꢁ
2
to form dianions of isonicotinic
x
the radical anions of CO
acid, as an intermediate (Eq. 4). Then, isonicotinic acid is
obtained through the oxidation of the intermediate (Eq. 5)
1
13
FTIR, H, and C NMR spectroscopy. The spectral character-
istics (see Figs. S1-S4 and Supporting Information) confirmed
[
33].
0
isonicotinicacidand4,4 -bipyridineasthefinalproductswith
yields of 80% and 20%, respectively. Therefore, it is logical to
Py þ COꢀ2ꢁ/PyCOO
ꢀ
ꢁ
2ꢁ
ðCÞ
(4)
(5)
ꢀꢁ
conclude that the radical anion of pyridine reacts with CO
2
and leads to the production of isonicotinic acid as the main
product. The coulometry current of pyridine in the presence
of CO
2
was also recorded for a long time (10 h) as in Fig. 7. The
ꢁ
2
O2
steadycurrentdensity (averagez1.32 mA cm ) implies that
2ꢁ
PyCOO /PyCOOH ðCÞ
x
no obvious deactivation of Cu/Cu O/Ni occurred during the
0
coulometry.
In summary, the proposed EC'C CC mechanism involves
three steps including one-electron electrocatalytic reduc-
0
ꢀꢁ
0
tion of CO
chemical reaction of Py and CO
2
(EC ) followed by reaction (3) to form Py (C ),
4. Conclusion
ꢀ
ꢁ
ꢀꢁ
2
(C) as shown in reaction
4) and, finally, oxidation of the produced intermediate
(
(
A Cu/Cu
trocatalyst, and the electrochemical reduction of CO
carried out by means of that electrode at a low over-
potential in an acetonitrile solvent. The Cu/Cu O/Ni elec-
trode was prepared by decorating the surface of a copper
foam with Cu O nanosheets and Ni nanorods (Cu/Cu O/Ni).
x
O/Ni electrode was fabricated as a new elec-
PyCOO2 ) to produce isonicotinic acid (C) in accordance
ꢁ
2
was
with reaction (5).
On the second track, two pyridine radical anions react
x
0
together and produce a 4,4 -bipyridine dimer, as shown in
Eqs. 6 and 7 [33].
x
x
Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
Comptes Rendus Chimie, https://doi.org/10.1016/j.crci.2019.09.007
2

8
S. Mohammadzadeh et al. / C. R. Chimie xxx (xxxx) xxx
As the results showed, the simultaneous use of Ni and
CuOeCu O (Cu O), rather than each one alone, in an elec-
trode increases its electrocatalytic activity for the reduction
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(
2
x
[
(
ꢀ
ꢁ
of CO
tion of CO
2
. CO
2
, as the product of the electrocatalytic reduc-
, was used for the electrosynthesis of isonicotinic
[
15] Y. Hori, R. Takahashi, Y. Yoshinami, A. Murata, J. Phys. Chem. B 101
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2
(
acid in mild conditions. The spectral characteristics of the
products indicated that, beside isonicotinic acid as the main
[
[17] D. Allam, S. Bennici, L. Limousy, S. Hocine, C. R. Chimie 22 (2019)
227.
0
product with the yield of 80%, 4, 4 -bipyridine was formed
[18] L. Angelo, K. Kobl, L.M.M. Tejada, Y. Zimmermann, K. Parkhomenko,
ꢀ
ꢁ
with the yield of 20%. CO
2
had a dual role in the electro-
A.C. Roger, C. R. Chimie 18 (2015) 250.
synthesis of isonicotinic acid. First, it induced the indirect
electrocatalytic reduction of pyridine to pyridine radical
anions. Second, it reacted with pyridine radical anions to
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[
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[
0
form isonicotinic acid based on an EC'C CC mechanism. The
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[
23] S. Nitopi, E. Bertheussen, S.B. Scott, X. Liu, A.K. Engstfeld, S. Horch,
B. Seger, I.E.L. Stephens, K. Chan, C. Hahn, J.K. Nørskov, T.F. Jaramillo,
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pyridine radical anions reacted with themselves to form 4,
0
4
-bipyridine based on the same mechanism. Furthermore,
as the data obtained through coulometry showed, long-
term use of the proposed electrode does not lead to any
noticeable loss of activity for CO electroreduction.
2
[24] H. Yang, Y. Huang, J. Deng, Y. Wu, N. Han, C. Zha, L. Li, Y. Li, J. Energy
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The authors are grateful for the support of the Iran Na-
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Utilization 27
Appendix A. Supplementary data
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2018) 1e10.
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2
(
[
Supplementary data to this article can be found online
at https://doi.org/10.1016/j.crci.2019.09.007.
230e247.
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Please cite this article as: S. Mohammadzadeh et al., Decoration of copper foam with Ni nanorods and copper oxide nanosheets to
produce a high-stability electrocatalyst for the reduction of CO : Characterization of the electrosynthesis of isonicotinic acid,
Comptes Rendus Chimie, https://doi.org/10.1016/j.crci.2019.09.007
2