Development of a new modified carbon paste electrode by silver chloride: Application to electrocatalytic oxidation of methanol

Article abstract of DOI:10.1007/s13738-015-0738-1

A new carbon paste electrode chemically modified with silver chloride is constructed. The silver chloride-modified carbon paste (SC-MCP) electrode was prepared by grinding the mixture of graphite powder and silicon oil (as a binder) with sufficient amount of silver chloride. Then, the electrode was placed in 0.1 mol L^-1 NaOH and the electrode potential was cycled between 170 and 800 mV (vs. Ag/AgCl) at a scan rate of 50 mV s^-1 for 20 cycles in a cyclic voltammetry regime until a stable voltammogram was obtained. The electrocatalytic activity of the SC-MCP electrode was examined for the oxidation of methanol. In CV studies, no oxidation response of methanol can be seen at the unmodified electrode, indicating the nonelectroactivity of methanol on this substrate. But at the SC-MCP electrode, a large anodic peak appears at 757.4 mV, indicating that the anodic oxidation of methanol could be catalyzed at SC-MCP electrode. This proves that the silver chloride bears the main role in electrocatalytic oxidation of methanol. Kinetic parameters such as the electron transfer coefficient (α) and the number of electrons involved in the rate-determining step (n _α) for the oxidation of methanol was determined utilizing cyclic voltammetry (CV). The modified electrode shows a stable and linear response in the concentration range of 5 × 10^-3-6 × 10^-2 mol L^-1 with a correlation coefficient of 0.9921.

Full text of DOI:10.1007/s13738-015-0738-1

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0738-1
ORIGINAL PAPER
Development of a new modified carbon paste electrode by silver
chloride: application to electrocatalytic oxidation of methanol
Ghasem Karim‑Nezhad1 · Sara Pashazadeh1
Received: 18 May 2014 / Accepted: 15 September 2015
© Iranian Chemical Society 2015
Abstract A new carbon paste electrode chemically modified
with silver chloride is constructed. The silver chloride-modified
carbon paste (SC-MCP) electrode was prepared by grinding the
mixture of graphite powder and silicon oil (as a binder) with
sufficient amount of silver chloride. Then, the electrode was
placed in 0.1 mol L−1 NaOH and the electrode potential was
cycled between 170 and 800 mV (vs. Ag/AgCl) at a scan rate of
50 mV s−1 for 20 cycles in a cyclic voltammetry regime until a
stable voltammogram was obtained. The electrocatalytic activ-
ity of the SC-MCP electrode was examined for the oxidation of
methanol. In CV studies, no oxidation response of methanol can
be seen at the unmodified electrode, indicating the nonelectro-
activity of methanol on this substrate. But at the SC-MCP elec-
trode, a large anodic peak appears at 757.4 mV, indicating that
the anodic oxidation of methanol could be catalyzed at SC-MCP
electrode. This proves that the silver chloride bears the main
role in electrocatalytic oxidation of methanol. Kinetic param-
eters such as the electron transfer coefficient (α) and the num-
ber of electrons involved in the rate-determining step (nα) for the
oxidation of methanol was determined utilizing cyclic voltam-
metry (CV). The modified electrode shows a stable and linear
response in the concentration range of 5 × 10−3–6 × 10−2 mol
Introduction
The mechanism and kinetics of methanol oxidation have
been studied under a wide range of conditions and on various
electrodes including Pt [1], binary and ternary alloys [2, 3],
modified electrodes [4, 5], nano composites [6, 7] and nickel
[8–10]. It has been shown that one promising approach for
minimizing over-voltage effects is through the use of an elec-
trocatalytic process at chemically modified electrodes [11, 12].
Carbon paste electrode (CPE) is a special kind of het-
erogeneous carbon electrode consisting of mixture pre-
pared from carbon powder (as graphite, glassy carbon
and other carbonaceous materials) and a suitable water-
immiscible or non-conducting binder [13]. The ease and
speed of preparation and of obtaining a new reproducible
surface, low residual current, porous surface, and low cost
of carbon paste are some advantages of CPE over all other
carbon electrodes. Therefore, CPE can provide a suitable
electrode substrate for preparation of modified electrodes
[14]. Modification of the paste matrix with various transi-
tion metal complexes [15–17] was reported in recent years.
These electrodes have been widely used in electroanalysis
due to their ability to catalyze the redox processes of some
molecules of interest, since they facilitate the electron
transfer [18].
L
−1 with a correlation coefficient of 0.9921.
Keywords Methanol · Modified carbon paste electrode ·
Electrocatalytic oxidation · Silver chloride · Cyclic
voltammetry
A variety of mediators ranging from organic molecules
to inorganic complexes such as prussian blue (PB) [19],
polyoxometalates [20, 21] and ruthenium complexes [22]
have been applied for the construction of CMCPE.
Ag is one of important metals and can be used not only
as modification metal but also as substrate metal in surface
modification [23]. We previously proved that the presence
of halides causes an increased activity in the electrocata-
lytic behavior of copper [24–26]. It seems that the presence
* Ghasem Karim-Nezhad
g.knezhad@gmail.com
1
Department of Chemistry, Payame Noor University, PO BOX
19395-3697, Tehran, Iran
1 3

J IRAN CHEM SOC
1200
1000
800
600
400
200
0
of halides can cause an increased activity in the electrocata-
lytic behavior of silver similar to copper.
1200
900
600
300
0
j
y = 7.437x + 344.87
R² = 0.9901
The results showed that in comparison to bare carbon
paste and silver electrodes, electrochemical behavior of
methanol has been greatly improved at silver chloride-
modified carbon paste (SC-MCP) electrode, indicating that
the anodic oxidation of methanol could be catalyzed at sil-
ver chloride-modified carbon paste electrode.
y = -3.4752x - 181.07
R² = 0.9902
-300
-600
-900
a
0
20
40
60
80
100
120
V( mvs-1
)
-200
-400
-600
Experimental
Reagents and instrumentation
0.17
0.27
0.37
0.47
0.57
0.67
0.77
0.87
E/V vs.Ag/AgCl
Methanol and other reagents were of analytical grade sup-
plied by Merck (Darmstadt, Germany) and Sigma Aldrich
and were used without further purification. Distilled water
was used for the preparation of all solutions. All electro-
chemical measurements were carried out in a three-electrode
cell using an Autolab electrochemical system (Eco Chemie,
Utrecht, the Netherlands) equipped with PGSTAT-12 and
GPES software. A bare or modified carbon paste electrode
(unmodified or modified) was used as a working electrode;
Ag/AgCl/saturated KCl and a Pt wire were used as reference
electrode and counter electrode, respectively. All experi-
ments were carried out at room temperature.
Fig. 1 Cyclic voltammograms of SC-MCP electrode in 0.1 mol
L−1 NaOH at various potential scan rates: a 10, b 20, c 30, d 40, e
50, f 60, g 70, h 80, i 90 and j 100 mV s−1. Inset The dependency
of anodic and cathodic peak currents vs. scan rate. (Inner to outer,
respectively)
2600
2200
Bare silver electrode in 50 mM methanol
Bare CPE in absence methanol
1800
Bare CPE in50 mM methanol
Sc-MCP electrode in abcence methanol
1400
SC-MCP in 50 mM methanol
Preparation of silver chloride‑modified carbon paste
electrode
1000
600
200
The carbon paste electrode modified with silver chloride
was prepared by hand mixing 71 % graphite powder, 9 %
silver chloride and 20 % paraffin oil in an agate mortar to
get homogeneous carbon paste. Then, paste was packed
into the end of a polyethylene syringe (2 mm in diameter).
A copper wire inserted into the carbon paste provided an
electrical contact. Before each measurement, pushing
an excess of paste out of the tube and then polishing the
freshly exposed paste with weighing paper obtained a new
surface. Also, unmodified carbon paste was prepared in the
same way but without adding silver chloride to the mix-
ture. Then, the electrode was placed in 0.1 mol L−1 NaOH
and the electrode potential was cycled between 170 and
800 mV (vs. Ag/AgCl) at a scan rate of 50 mV s−1 for 20
cycles in a cyclic voltammetry regime until a stable voltam-
mogram was obtained. The electrode was rinsed with dis-
tilled water, and applied for electrochemical studies.
-200
-600
-1000
-1400
-1800
0.17
0.27
0.37
0.47
0.57
0.67
0.77
0.87
E/V vs.Ag/AgCl
Fig. 2 Cyclic voltammograms of bare CPE, silver and SC-MCP
electrode in 0.1 mol L−1 NaOH solution in the absence and pres-
ence of 50 mmol L−1 methanol. Conditions: potential range—170–
850 mV scan rate of 50 mV s−1
the electrode was placed in 0.1 mol L−1 NaOH and the
electrode potential was cycled between 170 and 800 mV
(vs. Ag/AgCl) at a scan rate of 50 mV s−1 for 20 cycles
in a cyclic voltammetry regime until a stable voltammo-
gram was obtained (not shown). Results showed that with
increase of the scan number, the currents for both anodic
and cathodic peaks increase steadily for up to 20 runs. After
Results and discussion
Electrochemical properties of the prepared SC-MCP elec-
trode were investigated. For the activation of this electrode,
1 3

J IRAN CHEM SOC
Table 1 Comparison of some
electrochemical parameters of
SC-MCP electrode for methanol
oxidation with electrodes
reported in literature
Electrode
Ep(mV)
Ip(μΑ)
Tafel slope
α
J0(A cm−2
)
References
CCMCa
SOFMSb
Al/Pd/PoPD/Ptc
Pt|PoPD|CCEd
Ni/Al LDH/NMCCe
Pt|CCEf
820
1950
1169
4440
14,400
790
95
132
–
0.64
0.45
–
7.94 × 10−8
[24]
757.4
560
4.89 × 10−7
[28]
–
[30]
810
–
–
–
[33]
705
120.6
–
0.49
–
8.95 × 10−7
[37]
0.89
698.7
752
88,000
538.3
2265
–
[38]
Silver
SC-MCPg
119
83.8
0.496
0.66
2.40 × 10−8
8.85 × 10−7
Present work
Present work
a
CCMC copper chloride-modified copper electrode
b
c
d
e
f
Silver oxyfluoride-modified silver electrode
Poly(phenylenediamines) film palladized aluminum electrodes, modified by Pt micro-particles
Pt|PoPD|CCE Pt nanoparticles/poly(o-phenylenediamine) (PoPD)/carbon ceramic electrode
Ni/Al LDH/NMCC Ni/Al LDH nanoparticles modified carbon ceramic electrode
Pt|CCE Carbon ceramic electrode (CCE) modified with platinum particles
SC-MCP silver chloride-modified carbon paste electrode
g
20 runs, the SC-MCP electrode shows reproducible cyclic
voltammograms. A pair of redox peaks was observed which
correspond to the couple Ag(II)/Ag(I) can be described by
the reaction (1):
substrate. But at the SC-MCP electrode, a large anodic
peak appears at 757.4 mV. In the negative scan, there
is an oxidation peak at 500 mV, and it is caused by
reoxidation of intermediate product of methanol. The
great increase of the oxidized peak at 757.4 mV and the
deoxidized peak at 500 mV indicates that the SC-MCP
electrode displays preferable electrocatalytic activ-
ity toward methanol oxidation. Figure 2 also compares
the cyclic voltammogram of SC-MCP electrode with
that obtained by silver electrode. In comparison with
the data at silver electrode, an increase of threefolds
in peak current of methanol was observed at the SC-
MCP electrode. Our measurements using K4Fe(CN)6/
K3Fe(CN)6 system showed that the surface area of the
bare CPE, silver and SC-MCP electrodes is almost
the same. Thus, the increased activity of the electrode
related to the presence of halide. The increased activ-
ity probably related to a more favorable adsorption of
reactant or of intermediates leading to a higher sur-
face concentration of electroactive molecules ready
for being oxidized or it is due to the partial delocaliza-
tion of the electronic density of methanol into the solid
with possible consequent bond pre-dissociations which
facilitates the oxidation or both.
2AgCl + 2OH- (AgCl)2O + H2O + 2e-
(1)
Next, the cyclic voltammograms of the modified elec-
trode were recorded in 0.1 mol L−1 NaOH at various
potential sweep rates (Fig. 1). With the increase of the
scan rate, the redox current increased. The peak currents
(Ipa and Ipc) are proportional to sweep rates in the range of
10–100 mV s−1 (Inset of Fig. 2), which showed the elec-
trochemical activity of the surface redox couple. The value
of Γ* was 6.31 × 10−5 mol cm−2 for n = 2, which were
calculated from the slope of anodic peak current vs. scan
rate using [27]:
ꢀ
ꢁ
n2F2
Ip =
νAΓ ∗
(2)
4RT
where v is the sweep rate, A is the geometric surface area,
and Γ is the surface coverage of the redox species.
To reveal the electrocatalytic activity of SC-MCP
electrode toward the oxidation of methanol, the vol-
tammetric experiments were carried out on both modi-
fied and unmodified CPEs in the presence of methanol.
Figure 2 shows the cyclic voltammograms of SC-MCP
electrode in the absence and presence of methanol in
0.1 mol L−1 NaOH solution. As shown, no oxida-
tion response of methanol can be seen in the potential
range from 170 to 850 mV on unmodified electrode,
indicating the nonelectroactivity of methanol on this
Table 1 compares some electrochemical parameters
of SC-MCP electrode for methanol oxidation with elec-
trodes reported in literature. It was found that the elec-
trochemical behavior of methanol was improved at SC-
MCP electrode.
As suggested in literatures [24], the total oxidation
process of methanol consists of a pattern of paral-
lel reactions which can, in principle, be formulated as
follows:
1 3

J IRAN CHEM SOC
COad
(3)
HCHO, HCOOH
CO2
CH3OH
(adsorbed intermediates)
CO2
Both of these pathways require a catalyst, which should
be able to (a) dissociate the C-H bond and (b) facilitate
the reaction of the resulting residue with some O-contain-
ing species to form CO2 (or HCOOH). Generally accepted
methanol oxidation process consists of the following steps
that result in the formation of carboxyl intermediates and
strongly adsorbed CO species [24–26, 28–34]:
This is because the sites for adsorption increased with the
increase of silver chloride percentage in the modified electrode,
while the excess of silver chloride increases the resistance of
the electrode. Hence, a silver chloride (9 %, w/w)-modified
carbon paste electrode was used throughout this work.
The cyclic voltammograms of SC-MCP electrode were
recorded in different concentrations of NaOH solution con-
taining 30 mmol L−1 methanol (not shown). It is shown
that, the high catalytic peak current is achieved above
a NaOH concentration of 0.1 mol L−1. So, 0.1 mol L−1
NaOH was chosen as an optimum supporting electrolyte.
To provide more evidence, the effect of the scan rate vary-
ing from 5 to 100 mV s−1 on the voltammetric response of SC-
MCP electrode in a solution containing 30 mmol L−1 methanol
was studied (Fig. 4a). The anodic currents increase and the peak
potential shifts as the scan rate increases. When peak current
values were plotted against v1/2 (Fig. 4b), a linear relationship
with R2 = 0.9902 was obtained. This behavior suggests that the
oxidation process is controlled by diffusion. Moreover, a plot of
the scan rate normalized current (I/v1/2) vs. the scan rate exhibits
the typical shape of an electrochemical (EC′) catalytic process
(Fig. 4c). The peak currents for anodic oxidation of metha-
nol are not proportional to the scan rate. These results indicate
that at sufficiently positive potential the reaction is controlled
by surface-confined methanol species, which is the ideal case
for quantitative applications. Also, it can be seen that the peak
potential for the catalytic reduction of methanol shifts to more
positive values by increasing the scan rate, suggesting a kinetic
limitation in the reaction between the redox sites of silver chlo-
ride and methanol. A linear relationship was observed for Ep vs.
log ν (not shown) that can be expressed by the equation [27].
CH3OH + 2AgCl → AgCl · (CH3OH)ads
(4)
−
2AgCl · (CH OH) + 2OH →(AgCl) O · 2(CH OH)
3
3
ads
2
ads
−
+ H O + 2e
2
(5)
(6)
(AgCl) O · 2(CH OH) → 2AgCl · (CH O) + H OAS
3
3
2
2
ads
ads
2AgCl · (CH3O)ads + 2OH− →(AgCl)2O · 2(CH3O)ads
+ H2O + 2e−
(7)
(AgCl) O · 2(CH3O) → 2AgCl · (CH2O) + H2O
ads ads
(8)
2
2AgCl · (CH2O)ads + 2OH− →(AgCl)2O · 2(CH2O)ads
+ H2O + 2e−
(9)
(AgCl) O · 2(CH2O) → 2AgCl · (CHO)ads + H2O
ads
(10)
2
2AgCl · (CHO)ads + 2OH− →(AgCl)2O · 2(CHO)ads
+ H2O + 2e−
(11)
(12)
(AgCl)2O · 2(CHO)ads → 2AgCl · (CO)ads + H2O
2AgCl · (CO)ads + 2OH− →(AgCl)2O · 2(CO)ads
+ H2O + 2e−
(13)
(14)
2500
2000
1500
1000
500
(AgCl)2O · 2(CO)ads + H2O → 2AgCl · (COOH)ads
2AgCl · (COOH)ads + 2OH− →(AgCl)2O · 2(COOH)ads
+ H2O + 2e−
(15)
(AgCl)2O · 2(COOH)ads → 2AgCl + 2CO2 + H2O
(16)
0
The voltammetric signals were affected by the composition
of the paste. It was observed that the sensitivity of the sensor
first rapidly increases with increasing the silver chloride con-
tent in the paste up to about 9 %, and then started to level off
and even slightly decreases with the higher loadings (Fig. 3).
0
3
6
9
12
15
18
Silver chloride%
Fig. 3 Influence of silver chloride content in the carbon paste on the
electrode response in a solution containing 40 mmol L−1 methanol
1 3

J IRAN CHEM SOC
Fig. 4 a Cyclic voltammo-
grams of SC-MCP electrode in
0.1 mol L−1 NaOH containing
30 mmolL−1 of methanol at var-
ious potential scan rates (from
inner to outer) 7–100 mV s−1. b
Variation of the catalytic current
with the square root of sweep
rate. c Current function vs. v for
0.1 mol L−1 NaOH solution in
the presence of 30 mmol L−1
methanol
A
2000
1500
1000
500
k
a
0
-500
-1000
0.17 0.27 0.37 0.47 0.57 0.67 0.77 0.87 0.97
E/V vs.Ag/AgCl
B
C
1800
1500
1200
900
600
300
0
0.0065
0.006
0.0055
0.005
0.0045
0.004
y = 170.92x - 44.474
R² = 0.9902
0
0.02 0.04 0.06 0.08 0.1 0.12
V/vs-1
0
3
6
9
12
V0.5(mVs-1)0.5
chronoamperograms for the SC-MCP electrode in the
absence and presence of different concentrations of meth-
anol at an applied potential of 700 mV vs. Ag/AgCl. The
plot of net current with respect to the mines square roots of
time presents a linear dependency (Fig. 6b). This indicates
that the transient current must be controlled by a diffusion
process. The transient current is due to catalytic oxidation
of methanol, which increases as the methanol concentra-
tion is raised. No significant cathodic current was observed
when the electrolysis potential was stepped to 0.00 mV (vs.
Ag/AgCl), indicating the irreversible nature of the oxida-
tion of methanol.
Ep = b/2logv + k
(17)
On the basis of Eq. (17), the slope of Ep vs. logν plot is
b/2, where b indicates the Tafel slope. The slope of Ep vs.
log ν plot is ∂Ep/∂ (logv) which was found to be 51.96, so
b = 103.92. This slope indicates that a one-electron trans-
fer process is the rate-limiting step assuming a transfer
coefficient of α = 0.57 for methanol.
With the increase of methanol concentration, the anodic
peak current gradually increased (Fig. 5). The characteris-
tic shape of cyclic voltammogram in this potential region
indicates that the signal is due to the oxidation of methanol.
The catalytic peak current is proportional to the concentra-
The rate constants of the reactions of methanol and the
ensuing intermediates with the redox sites of the SC-MCP
electrode can be derived from the chronoamperograms
according to Eq. (18) [27]:
tion of methanol in the range of 5 mmol L−1–60 mmol L−1
.
The linear regression equation is I (µA) = 30.357 C methanol
(mmol L−1) + 894.24 (R2 = 0.9947).
To evaluate the reaction kinetics, the oxidation of meth-
anol on SC-MCP electrode was investigated by chrono-
amperometry. Chronoamperometry, as well as cyclic vol-
tammetry has been employed for the investigation of the
processes occurring via an ErCi mechanism [35]. Double
steps chronoamperograms were recorded by setting the
working electrode potentials to desired values and were
used to measure the catalytic rate constant on the modi-
fied surface. Figure 6a shows a series of well-defined
ꢀ
ꢁ
ꢂ
ꢃ
Icatal/Id = ꢀ1/2
π
1/2erf ꢀ1/2 + exp(−ꢀ)/ꢀ1/2
(18)
where Icatal is the catalytic current in the presence of metha-
nol, Id the limiting current in the absence of methanol and
λ = kCt (k, C and t are the catalytic rate constant, bulk con-
centration of methanol and the elapsed time, respectively)
is the argument of the error function. For λ > 1.5, erf (λ1/2
)
almost equals unity and Eq. (19) reduces to [27]:
1 3

J IRAN CHEM SOC
1700
1500
1300
1100
900
3100
2600
2100
1600
1100
600
A
A
350
300
250
200
150
100
50
m
a
y = 13.524x + 8.1
R² = 0.9909
0
700
0
5
10
15
20
25
Concentration of methanol/ mmol L-1
500
e
300
100
a
-100
100
0
10
20
30
40
50
60
t/ s
-400
-900
-1400
-1900
B
750
600
450
300
150
0
e
0.17
0.27
0.37
0.47
0.57
0.67
0.77
0.87
a
E/V vs.Ag/AgCl
0
0.2
0.4
0.6
0.8
t-0.5/ s-0.5
B
3000
2500
2000
1500
1000
500
C
20
18
16
14
12
10
y = 30.357x + 894.24
R² = 0.9947
y = 2.7269x + 8.3868
R² = 0.996
0
1
1.5
2
2.5
3
3.5
0
20
40
60
80
Concentration of methanol/ mmol L-1
t0.5 / s0.5
Fig. 6 a Chronoamperograms of SC-MCP electrode in 0.1 mol L−1
NaOH containing different concentrations of methanol: 0.0, 5, 10, 15
and 20 mmol L−1, from a to e, respectively. Potential steps were 0.65
and 0.0 V, respectively. Insets variation of chronoamperometric cur-
rents at t = 15 s vs. concentration of methanol. b Plot of i vs. t−1/2
obtained from chronoamperometric measurements SC-MCP elec-
trode in 0.1 mol L−1 NaOH containing different concentrations of
methanol: 0.0, 5, 10, 15 and 20 mmol L−1, from a to e, respectively. c
Dependency of Icatal/Id on t1/2 derived from CAs of a and e in panel A
Fig. 5 a Cyclic voltammograms of a SC-MCP electrode in the pres-
ence of various methanol concentrations: a–j: 5, 10, 15, 20, 25, 30,
35, 40, 45, 50, 55 and 60 mmol L−1, respectively, at a scan rate of
50 mV s−1, in 0.1 molL−1 NaOH solution. b Variation of anodic peak
current vs. methanol concentration
Icatal/Id = ꢀ1/2π1/2(kCt)1/2
(19)
From the slope of the Icatal/Id vs. t1/2 plot (Fig. 6c),
the value of k for 20 mmol L−1 methanol was calcu-
To obtain information on the rate-determining step, Tafel
plots were drawn under a controlled rotating disc speed at
different methanol concentrations (Inset of Fig. 7), derived
from data of the rising part of the current–voltage curves at
a low scan rate of 7 mV s−1. The anodic electron transfer
coefficient of α = 0.69 and the exchange current density
(j0) of 8.85 × 10−7 Acm−2 were obtained.
lated to be 1.175 × 105cm3 mol−1 s−1
.
The pseudo-steady-state polarization curves of the
electro-oxidation of methanol on SC-MCP electrode at
a number of methanol concentrations are presented in
Fig. 7. The rotation rate of the electrode is maintained
at 3000 rpm to avoid the interference of the mass trans-
fer in the kinetic measurements. The oxidation process
was found to begin at nearly 515 mV (vs. Ag/AgCl)
and to reach a plateau at 605 mV (vs. Ag/AgCl), while
the oxygen evolution starts at still higher potentials. In
the course of reaction, the coverage of Ag(II) increases
and reaches a saturation (steady state) level and the
oxidation current follows accordingly.
Analytical characteristics of SC-MCP electrode for the
amperometric determination of methanol were estimated.
Figure 8 shows the current–time responses of the modified
electrode to methanol which was successively added to the
electrochemical cell containing 0.1 mol L−1 NaOH under
hydrodynamic conditions, while the electrode potential was
kept at 0.6 V. As shown in the figure, a well-defined response
1 3

J IRAN CHEM SOC
0.55
300
the modified CPE. It was found that the relative standard devi-
ation (R.S.D.) of the peak currents of 30 mmol L−1 methanol
for seven replicate determinations was 2.7 %.
0.53
250
200
150
100
50
0.51
0.49
0.47
0.45
d
a
Conclusion
-6.5
-6
-5.5
logI/A
-5
-4.5
-4
In the present study, the electrochemical behaviors of
methanol at SC-MCP electrode have been investigated.
The modified electrode exhibits excellent and persistent
electrocatalytic behavior toward methanol oxidation com-
pared with the bare carbon paste electrode. For SC-MCP
electrode, kinetic parameters such as the electron transfer
coefficient (α), catalytic reaction rate constant (k) and the
number of electrons involved in the rate-determining step
(nα) for oxidation of methanol at the SC-MCP surface were
calculated as 0.66, 1.175 × 105 and 1, respectively.
0
0.44
0.46
0.48
0.5
0.52
0.54
0.56
0.58
0.6
E/V vs.Ag/AgCl
Fig. 7 a Pseudo-steady-state polarization curves of SC-MCP elec-
trode obtained in 5 (a), 10 (b), 15 (c) and 20 mmol L−1 methanol (d),
respectively. The potential sweep rate is 5 mV s−1. (Inset) Tafel plots
derived from the rising part of voltammograms recorded at a scan rate
5mV s−1
450
References
400
400
350
300
250
200
150
100
300
200
100
0
1. H. Nonaka, Y. Matsumura, J. Electroanal. Chem. 520, 101
(2002)
2. C.L. Green, A. Kucernak, J. Phys. Chem. B 106, 1036
(2002)
3. A.S. Arico, Z. Poltarzewski, H. Kim, A. Morana, N.
Giordano, V. Antonucci, J. Power Sources 55, 159 (1995)
4. M. Jafarian, M.G. Mahjani, H. Heli, F. Gobal, H. Khajeshar-
ifi, M.H. Hamedi, Electrochim. Acta 48, 3423 (2003)
5. S.M. Golabi, A. Nozad, Electroanalysis 15, 278 (2003)
6. F.E. Jones, S.B. Milen, B. Gurau, E.S. Smotkin, S.R. Stock,
C.M. Lukehart, J. Nanosci. Nanotechnol. 2, 81 (2002)
7. J. Luo, M.M. Maye, Y. Lou, L. Han, M. Hepel, C.J. Zhong,
Catal. Today 77, 127 (2002)
y = 1.0567x + 89.52
R² = 0.9978
0
50
100
150
200
250
Concentration of methanol/ μmol L-1
0
100
200
300
400
t/s
500
600
700
800
8. A.A. El-Shafei, J. Electroanal. Chem. 471, 89 (1999)
9. M.S. Kim, T.S. Hwang, K.B. Kim, J. Electrochem. Soc. 144,
1537 (1997)
Fig. 8 The current time profiles recorded at the SC-MCP electrode
during the successive addition of methanol. Inset typical calibration
graph derived from the current–time profile
10. M.A. Abdel Rahim, R.M. Abdel Hameed, M.W. Khalil, J.
Power Sources 134, 160 (2004)
11. M.A. Abdel Rahim, H.B. Hassan, R.M. Abdel Hamid, J.
Power Sources 154, 59 (2006)
12. S.M. Golabi, A. Nozad, Electroanalysis 16, 199 (2004)
13. K. Kalcher, Electroanalysis 2, 419 (1990)
14. Hamid R. Zare, Navid Nasirizadeh, Int. J. Electrochem. Sci.
4, 1691 (2009)
was observed during the stepwise increasing of methanol
concentration in the range 60–220 µmol L−1. The linear
regression equation of calibration curve is expressed as I
(µA) = 1.0567 C methanol µmol L−1 +89.52 with a correlation
coefficient of 0.9978 (n = 9). A calibration plot constructed
from data of Fig. 8 gives a limit of detection (LOD) and sen-
sitivity 8.21 and 1.0567µA/µmol L−1, respectively [36].
By repetitive CV of the SC-MCP electrode for approxi-
mately 20 times in NaOH solution at a scan rate of 50 mV s−1,
the peak current value decreases less than 9 %, indicating
good stability. The modified electrode retained its initiate
activity for more than 40 days when kept in air at ambient
conditions. A decrease of 12 % was observed in the current
response of the electrode at the end of 40th day. In addition,
repetitive recording of cyclic voltamograms in methanol solu-
tion tested the reproducibility of the electrocatalytic effect of
15. K.I. Ozoemena, R.S. Staden, T. Nyokong, Electroanalysis
21, 1651 (2009)
16. S. Shahrokhian, M. Amiri, Solid State. Electrochem. 11,
1133 (2007)
17. E.V. Ivanova, V.S. Sergeeva, J. Oni, Ch. Kurzawa, A.D. Rya-
bov, W. Schuhmann, Bioelectrochem. 60, 65 (2003)
18. M. Amiri, Z. Pakdel, A. Bezaatpour, S. Shahrokhian, Bioel-
ectrochemistry 81, 81 (2011)
19. D. Moscone, D.DQOttavi, D. Compagnone, G. Palleschi.
Anal. Chem. 73, 2529 (2001)
20. X.L. Wang, E.B. Wang, Y. Lan, C. Hu, Electroanalysis 14,
1116 (2002)
21. B.R. Limoges, R.J. Stanis, J.A. Turner, A.M. Herring, Elec-
trochim. Acta 50, 1169 (2005)
22. X.L. Wang, Z.B. Han, H. Zhang, E.B. Wang, C.W. Hu, Elec-
troanalysis 15, 1460 (2003)
1 3

J IRAN CHEM SOC
23. C. Jin, Z. Zhang, Z. Chen, Q. Chen, Electrochim. Acta 87,
860 (2013)
31. F. Vigier, F. Gloaguen, J.M. Léger, C. Lamy, Electrochim.
Acta 46, 4331 (2001)
24. G. Karim-Nezhad, P.S. Dorraji, Electrochim. Acta 55, 3414
(2010)
25. G. Karim-Nezhad, B. Zare Dizajdizi, P.S. Dorraji, Catal.
Communi. 12, 906 (2011)
32. P. Ross, N. Markovic, CATTECH 4, 110 (2000)
33. H. Razmi, E. Habibi, J. Solid State Electrochem. 13, 1897
(2009)
34. H. de Santana, M.L.A. Temperini, J. Electroanal. Chem.
316, 93 (1991)
26. G. Karim-Nezhad, A. Pashazadeh, S. Pashazadeh, J. Korean
Chem. Soc. 57, 322 (2013)
35. A.J. Bard, L.R. Faulkner, Electrochemical methods: funda-
mentals and applications, 2nd edn. (Wiley, New York, 2001)
36. J.C. Miller, J.N. Miller, Statistics for Analytical chemistry,
2nd edn. (Prentice Hall, New York, 1994)
27. M. Hasanzadeh, G. Karim-Nezhad, N. Shadjou, B. Khalilza-
deh, L.A. Saghatforoush, S. Earshad, I. Kazeman, Chin. J.
Chem. 27, 638 (2009)
28. G. Karim-Nezhad, S. Pashazadeh, A. Pashazadeh, Anal. Bio-
37. G. Karim-Nezhad, S. Pashazadeh, A. Pashazadeh, Chin. J.
Catal. 33, 1809 (2012)
anal. Electrochem. 5, 719 (2013)
29. L. Niu, Q. Li, F. Wei, S. Wu, P. Liu, X. Cao, J. Electroanal.
Chem. 578, 331 (2005)
38. H. Razmi, Es. Habibi, H. Heidari. Electrochim. Acta 53,
8178 (2008)
30. M.H. Pournaghi-Azar, B. Habibi, J. Electroanal. Chem. 601,
53 (2007)
1 3