2
S. Mohammadzadeh et al. / Electrochimica Acta 352 (2020) 136483
ꢀ
ꢁ
reduced form of 4-nitrobenzyl bromide with CO
2
to form 4-
XMU. The morphology of the modified electrodes was deter-
mined by atomic force microscope (AFM) images (Nanosurf,
Switzerland) and X-ray powder diffraction (XRD) patterns were
nitrophenylacetate. It is to be noted that 4-nitrophenylacetate de-
rivatives have been widely used as a mediator in the synthesis of
different medicines such as antitumor agents [25] and deprotecting
reagents [26]. To improve the performance of 4-nitrobenzyl bro-
taken in reflection mode CuK
a
(
l
¼ 1.5406 Å) radiation in the 2
q
ꢂ
ꢂ
range from 10 to 80 on a senware AW-DX300 X-ray diffractom-
eter. Electrochemical impedance spectroscopy (EIS) tests were
conducted at a steady-state potential. An AC amplitude potential of
10 mV superimposed on a DC potential was applied, and a fre-
quency span of 100 KHz down to 10 mHz was scanned. The Nyquist
plots of impedance data were analyzed using ZsimpWin software.
2
mide electrocatalyst toward the reduction of CO , a new nano-
composite of Cu nanoparticles/Pd nanoparticles/reduced graphene
oxide (Cu/Pd/rGO) was prepared via the simple electrodeposition
methods on the GCE surface. rGO is considered as support catalyst
[
27,28] because of its unique structure and properties, high specific
1
13
surface area, high electrical conductivity, great mechanical stability,
ease of preparation, low cost [29,30] and strong nanoparticle
anchoring [28,31]. Direct electrochemical reduction of graphene
oxide (GO) to rGO on the electrode surface is faster, more envi-
ronmentally friendly, and easier to control [32,33] than using
reducing agents such as hydrazine [34,35], sodium borohydride
H and C NMR were measured on a DRX-400 (Bruker) spec-
trometer with CDCl as a solvent in the presence of SiMe as an
3
4
internal standard. Fourier transform infrared (FTIR) spectrum
analysis was performed on an EQUINOX55 spectrometer.
2.2. Preparation of Cu/Pd/rGO/GCE
[
36] and ascorbic acid [37]. Applying composites of
grapheneemetal nanoparticles have attracted extensive attention
which is due to their enhance electron conductivity, high surface
area, catalytic properties and good biocompatibility [38e40]. Re-
searchers have reported that Pd and graphene bind strongly
because of generated interaction states and transmission channels
between them [41e43]. In other words, GO sheets act as scaffolds to
grow and anchor Pd nanoparticles (PdNPs) [44]. Because of some
attractive properties such as good electrical conductivity and cat-
alytic properties of copper nanoparticles (CuNPs) [45], it was also
used for electrode modification. In other words, CuNPs/PdNPs/rGO
modified GCE (Cu/Pd/rGO/GCE) was used for electrocatalytic
Prior to modification, the GCE surface was polished with a
0.05
was washed with double distilled water and sonicated for a few
minutes. For preparation of rGO modified GCE (rGO/GCE), 10.0
mm alumina slurry on a polishing cloth. The polished electrode
m
L
ꢁ
1
homogeneous suspension of GO (1 mg mL ) was dropped on the
polished GCE surface and dried in air to form GO/GCE, then it was
placed in a phosphate buffer (pH 5) to be reduced electrochemically
in the potential range of 0.5 V to ꢁ1.5 V and at potential scan rate of
ꢁ1
100.0 mV s . Finally, it was then washed and dried [32,33,49].
Next, Pd nanoparticles are electrochemically deposited on rGO/GCE
surface [50]. The electrode was immersed into a 0.5 M H
2
SO
lution containing 1.0 ꢃ 10 M potassium tetrachloro palladate (II),
and repetitive potential scan carried out between 1.2
4
so-
ꢁ
3
2
reduction of CO by 4-nitrobenzyl bromide. Objective of this paper
is to present the performance of 4-nitrobenzyl bromide, as an
a
V
ꢁ1
excellent mediator, for electrocatalytic reduction of CO
2
at the Cu/
and ꢁ0.25 V with scan rate of 100 mV s for seven cycles. Then,
produced Pd/rGO/GCE was rinsed with deionized water. To prepare
Cu/Pd/rGO/GCE, electrodeposition method was used easily in sul-
phuric acid solution (pH 1.5) containing 0.025 M copper sulphate
by consecutive cyclic voltammetry (30 scans) in the potential range
of 0.5 V to ꢁ0.6 V and at scan rate of 100 mV sꢁ [51].
Pd/rGO nanocomposite modified electrode surface.
2
. Experimental
1
2.1. Chemicals and apparatus
4
-Nitrobenzyl bromide (99%), tetrabuthyl ammonium perchlo-
2.3. Electrolysis procedure
rate (TBAP) (>98.0%), potassium tetrachloro palladate (II) (98%),
copper (II) sulphate (99%), acetonitrile solvent (ACN) (99.9%) were
purchased from Merck Company. Acetonitrile (ACN) were purified
All the electrolysis experiments were performed at constant
potential coulometry (CPC) in 50.0 ml of ACN solution containing
0.05 M TBAP. Before each experiment, a definite amount of 4-
nitrobenzyl bromide was added to the solution, and Ar gas was
bubbled for 20 min. During the electrolysis, consumption of the
initial compound, i.e. 4-nitrobenzyl bromide, was followed by TLC
tests of aliquots withdrawn from the reaction mixture. In the TLC
tests, the spots were identified by irradiation of ultraviolet light. At
the end of the electrolysis, 5.0 mL of 0.5 M HCl was added to the
solution, and it was stirred for 30 min at room-temperature. Af-
terwards, the solvent was evaporated, and the residue was sepa-
rated with a silica gel column under gradient elution. The result of
according Ref [46]. ACN was treated with heated neutral A1
6
2
O
3
at
00 C under vacuum (3 h) and then was passed through molecular
sieves 4 Å (B.D.H.). The obtained solvent was distilled under N flux
at pressure of 4e5 Torr and finally was collected over P . TBAP
ꢂ
2
2 5
O
recrystallized from an ethanol solution and was dried under vac-
ꢂ
uum at 60 C [46,47]. A phosphate buffer (pH 5) was prepared with
0
.1 M H
3
PO
4
and 2.0 M NaOH. GO was prepared based on the
and Ar had a purity
modified Hummers’ method [48]. Gases of CO
2
of 99.995%. All the measurements were performed at room tem-
perature. Cyclic voltammetry was carried out using an EG&G
PARSTAT 2273 equipped with a Power Suite software program in a
conventional three-electrode electrochemical cell containing bare
and various modified GCE with a diameter of 2 mm as the working
electrode, Ag/AgCl/KCl (sat’d) as the reference electrode, and a Pt
wire as the counter electrode. A SAMA 500 electroanalyzer was
used for constant potential coulometry (CPC) experiments. Divided
and undivided glass cells were used in the electrolysis and vol-
tammetric experiments, respectively. The cells were equipped each
with a gas inlet and outlet, a graphite rod as the cathode, an Ag/
2
the 4-nitrobenzyl bromide electrolysis in the absence of CO (under
an Ar flow) and at the constant potential of ꢁ0.89 V showed con-
ꢁ1
sumption of about 1.1 F mol . Under these conditions, the Faradaic
yield in the bare GCE and various modified electrodes surface is
1
about 91%. Also, the H NMR spectral characteristics of the product
were as follows:
d
3.09 ppm (s, 4H),
d
7.55 ppm (d.d, 4H, j ¼ 3.2),
d
7.72 ppm (d.d, 4H, j ¼ 3.2) which are related to 1,2-bis(4-
nitrophenyl) ethane compound (Fig. S1). The approximate yield of
this product at the surface of various electrodes was reported in
AgCl/KCl (sat’d) electrode as the reference and a platinum plate
Table 1. The electrolysis of 4-nitrobenzyl bromide under bubbling of
2
ꢁ1
(
ca.5 cm ) as the anode. Acetonitrile and TBAP were used as a
CO
presence of CO
modified electrodes surface is about 98%. Final products in the
presence of CO were 4-nitrophenylacetate and oxalate as the main
2
at the potential of ꢁ0.80 V consumed about 2.04 F mol . In the
solvent and a supporting electrolyte respectively. Surface mor-
phologies were analyzed with high-resolution field emission
scanning electron microscopy (FESEM), model MIRA3TESCAN-
2
, the Faradaic yield at the bare GCE and the various
2