1. 1 23
Journal of Solid State
Electrochemistry
Current Research and Development in
Science and Technology
ISSN 1432-8488
Volume 19
Number 8
J Solid State Electrochem (2015)
19:2235-2244
DOI 10.1007/s10008-015-2847-2
Silver nanoparticles/poly ortho-toluidine/
modified carbon paste electrode as a stable
anode for hydrazine oxidation in the
alkaline media
Reza Ojani, Ali Alinezhad, Mohammad
Ja’far Aghajani & Saeid Safshekan

2. 1 23
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3. ORIGINAL PAPER
Silver nanoparticles/poly ortho-toluidine/modified carbon paste
electrode as a stable anode for hydrazine oxidation
in the alkaline media
Reza Ojani1
& Ali Alinezhad1
& Mohammad Ja’far Aghajani1
& Saeid Safshekan1
Received: 10 October 2013 /Revised: 20 May 2014 /Accepted: 1 April 2015 /Published online: 24 April 2015
# Springer-Verlag Berlin Heidelberg 2015
Abstract Silver nanoparticles were deposited on the surface
of poly ortho-toluidine (POT) modified carbon paste electrode
(n-Ag/POT/MCPE) by the electrochemical method. The elec-
trocatalytic activity of the prepared modified electrode toward
the hydrazine oxidation in alkaline solutions was evaluated
using cyclic voltammetry (CV) and chronoamperometry
(CHA) methods. The CV experiment showed that the n-Ag/
POT/MCPE electrode is electrochemically active toward the
hydrazine oxidation, and a sharp increment in the current of
hydrazine oxidation was observed with the increase of the
hydrazine concentration. CHA results show stable steady state
current (Iss) for the hydrazine oxidation. A linear dependence
of the Iss upon the hydrazine concentration was found in the
range of 1.0×10−4
to 6.0×10−3
M hydrazine. Results imply
that the n-Ag/POT/MCPE presents stable and significantly
high electroactivity for the hydrazine oxidation.
Keywords Electrocatalysis . Silver nanoparticles . Hydrazine
oxidation . ortho-Toluidine
Introduction
Hydrazine is a highly reactive base and reducing agent which
is primarily used as a high-energy rocket propellant, as a re-
actant in military fuel cells, in nickel plating, in the polymer-
ization of urethane, for removal of halogens from wastewater,
as an oxygen scavenger in boiler feed water to inhibit corro-
sion, and in photographic development [1]. Hydrazine was
historically used as a therapeutic agent in the treatment of
tuberculosis, sickle-cell anemia, and non-specific chronic ill-
nesses [1]. The Environmental Protection Agency (EPA) has
reported hydrazine and its derivatives as environmental pol-
lutants, and the maximum recommended value of hydrazine in
effluents is set to 0.0001 % [2].
Considerable attention has been given to direct liquid fuel
cells, such as the methanol, formic acid, hydrazine, and boro-
hydride systems because of their high energy capacity com-
pared to advanced batteries [3].
For the direct hydrazine fuel cell, its most attractive feature
may be higher theoretical cell voltage of 1.57 V according to
the anode reaction (1) and cathode reaction (2) in alkaline
solutions:
N2H4 þ 4OH−
→N2 gð Þ þ 4H2O þ 4e E¨
¼ −1:16V vs:SHE ð1Þ
O2 þ 2H2O þ 4e → 4OH−
E¨
¼ 0:41V vs:SHE ð2Þ
However, oxidation of hydrazine on the surface of ordinary
electrodes suffers from high overpotential. Thus, there have
been increasing reports for the investigation of hydrazine oxi-
dation by various electrocatalysts [4–9]. Electrooxidation of
hydrazine at gold [10], nickel [11], and mercury [12] electrodes
has been studied. Hydrazine oxidation on single-crystal plati-
num surfaces (1 1 1) and (3 2 2) were studied by Chizuko
Nishihara and coworkers [13]. Their work showed that the
electrochemical oxidation of hydrazine at Pt electrode requires
a higher overpotential. The electrochemical oxidation of hydra-
zine at a silver electrode was reported by Korinek [14].
The electrooxidation of hydrazine at the carbon paste elec-
trode is a simple and cheap approach, but its kinetics are slow
and needs to high overpotentials. In order to resolve this prob-
lem, electrocatalytic modified electrodes based on a variety of
* Reza Ojani
fer-o@umz.ac.ir
1
Electroanalytical Chemistry Research Laboratory, Faculty of
Chemistry, University of Mazandaran, Babolsar, Iran
J Solid State Electrochem (2015) 19:2235–2244
DOI 10.1007/s10008-015-2847-2
Author's personal copy

4. catalysts including metals, polymer films, and metal complexes
were used. Different redox mediators such as various transition
metal hexacyanoferrates [15], ferrocencarboxylic acid [16], and
metal phethalocyanines [17] have been used in modifying car-
bon paste electrodes for hydrazine oxidation. Cobalt complexes
have been applied as mediators to modify carbon paste elec-
trodes in order to obtain a catalytic activity for hydrazine oxi-
dation [18]. A modified carbon paste electrode prepared by
using tetracyanoquinodimethanide adsorbed on silica modified
with titanium oxide showed an excellent catalytic activity and
stability for hydrazine oxidation [19].
A lot of research studies have demonstrated that coating the
electrode surface with conducting polymers (CPs) is an attrac-
tive approach for enhancing the power and scope of electro-
chemically modified electrodes [20, 21]. CP matrices have
been employed as catalyst support materials for the oxidation
of small molecules in place of conventional supports, because
when a catalyst is dispersed in carbon black, a part of the
active sites remains inaccessible to the reactant molecules.
The reason for incorporating metallic particles into the porous
matrixes is to increase the specific area of these materials and
thereby improve catalytic efficiency [22].
Among different materials, metal nanoparticles have
attracted much attention due to their unique properties and
wide varieties of potential applications in various areas includ-
ing catalysis, magnetic materials, information storage, micro-
electronics, and optoelectronics. Among various
nanocatalysts, silver nanoparticles serve as an encouraging
candidate due to its high activity in alkaline solutions. It is
known that silver possesses a higher electrical conductivity
and is approximately 100 times less expensive than platinum
[23]. Several approaches, such as electroless plating and metal
nanowire [24], chemical reduction [25], electrochemical de-
position [26], and ion beam assisted deposition [27], have
been developed to synthesize Ag structures.
In the present study, we have fabricated a nanosilver sup-
ported poly ortho-toluidine modified carbon paste electrode
using electrochemical polymerization and Ag deposition pro-
cesses to obtain a new electrocatalyst for hydrazine oxidation.
Experimental
Reagents and materials
Sodium hydroxide (from Merck), hydrazine hydrate (80 %)
(from Merck), silver nitrate (from Fluka), ortho-toluidine (OT)
(from Merck), and distilled water were used.
Instrumentation
The electrochemical experiments were performed using
potentiostat/galvanostat (BHP 2061-C-Electrochemical
Analysis System, Behpajooh, Iran) coupled with a Pentium
IV personal computer. The utilized three-electrode system was
composed of Ag/AgCl/KCl (sat’d) as reference electrode, a
platinum wire as auxiliary electrode, unmodified carbon paste
electrode, and silver nanoparticles/poly ortho-toluidine/modi-
fied carbon paste electrode (n-Ag/POT/MCPE) as working
electrode substrates.
Synthesis and characterization of the n-Ag/POT/MCPE
The unmodified carbon paste was prepared by thoroughly
mixing 1.0 g carbon powder with paraffin oil in a mortar.
The resulting paste was then inserted in the bottom of a glass
tube. The electrical connection was implemented by a copper
wire lead fitted into the glass tube. A fresh electrode surface
was generated rapidly by extruding a small plug of the paste
out of the tube and smoothing the resulting surface on white
paper until a smooth shiny surface was observed.
The electrochemical preparation of POT films was carried
out by cyclic voltammetry from 0.0 to 1.2 V versus Ag/AgCl/
KCl with the scan rate of 50 mV s−1
in an aqueous solution
containing 3.0 mM OT and 0.5 M H2SO4 up to reach 10 com-
plete cycles. Freshly prepared POT films were washed with
distilled water and monomer-free electrolyte solution. After that,
they were dipped into a 5 mM silver nitrate solution at room
temperature for 20 min. This procedure allowed for physical
adsorption of silver ions into the POT film. In order to stabilize
the silver nanoparticles, the electrode transfer in 0.1 M NaOH
solution and 10 successive potential cycling from −0.4 to 0.9 V
versus Ag/AgCl/KCl with the scan rate of 100 mV s−1
were
performed. Schematic 1 shows the sequence of steps.
Results and discussion
Cyclic voltammetric study of POT/MCPE
The poly ortho-toluidine (POT) film was prepared on the surface
of the carbon paste electrode. Figure 1 shows the typical multi-
sweep cyclic voltammograms during the electropolymerization
of OT in the 0.5 M H2SO4 solution. As can be seen, in the first
anodic sweep, the oxidation of OT occurs as a distinct irrevers-
ible anodic peak (Ep=0.92 V). A part of the oxidation products
of OT is deposited on the electrode, as a POT film. In the second
positive scan of potential, a new anodic peak is found at a po-
tential around 0.44 V which is due to the oxidation of resulting
polymeric film. The oxidation peak current of monomer is de-
creased with increasing of the number of potential cycles. The
decreasing of oxidation current is due to the loss of activity of
the electrode surface when covered with a newly formed poly-
mer film [22]. In the second reverse cycle, the new cathodic
peak is found at a potential around 0.30 V, confirming the initial
deposition of electrooxidized products. Under successive
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5. potential cycling, the peak currents related to the polymer are
significantly increased. Moreover, the monomer oxidation po-
tential is shifted to positive potentials, and its oxidation current
decreased.
Cyclic voltammetric experiments of n-Ag/POT/MCPE
Figure 2 shows scanning cyclic voltammetry (CV) profile of
the n-Ag/POT/MCPE in 0.1 M NaOH solution. It is found that
the n-Ag/POT/MCPE exhibits high anodic and cathodic cur-
rents, showing a large surface area of the modified electrode.
Overlapped CV curves were observed to be increased with
cycling numbers and then to be stable after 10 cycles which
shows the stabilization of catalyst nanoparticles on the POT/
MCPE surface (Fig. 2).
In the anodic oxidation range of silver, four anodic peaks,
A1 at 0.28 V, A2 at 0.35 V, A3 at 0.72 V, and A4 at 0.58 V, were
obtained as shown in Fig. 2. From the cyclic voltammogram
depicted in this figure and the literature, a scheme pathway for
transitions during the potential cycling can be presented as
follows:
The first small anodic peak (A1) which is found as a shoul-
der at around 0.28 Vis related to mix of initial oxidation of Ag
to Ag(OH)2
−
through adsorption of OH−
and formation and
precipitation of a monolayer of Ag2O from supersaturated
solution of Ag(OH)2
−
, which progressively blocks off the dis-
solution reaction of Ag to Ag(OH)2
−
[28, 29].
Ag þ 2OH−
ads→Ag OHð Þ2
−
ads þ e−
ð3Þ
Ag OHð Þ2
−
ads→ Ag OHð Þ2
−
aq→Ag2O ð4Þ
According to Droog [29], the peak A2 is due to the forma-
tion of multilayer of Ag2O caused by the following reaction:
2Ag þ 2OH−
→Ag2O þ H2O þ 2e−
ð5Þ
The further forward potential sweep leads to the arising of
the peak A3 at 0.72 V which is attributed to the formation of
high-valence silver oxide (AgO):
Ag2O þ 2OH−
→2AgO þ H2O þ 2e−
ð6Þ
Scheme 1 Schematic procedure
for construction of the n-Ag/POT/
MCPE
Fig. 1 Electrochemical polymerization of OT in 3.0 mM OT + 0.5 M
H2SO4 solution (at E=0.0 to1.2 V and =0.05 V s−1
)
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6. In the reverse scan, one oxidation peak, A4, and two
reduction peaks, C1 and C2, were delivered at 0.58,
0.40, and 0.05 V, respectively. During the cathodic
sweep, oxidation peak A4 is reported to be attributed
to continuous nucleation and growth of Ag2O film as
a result of direct electrooxidation of Ag metal [30]. Two
cathodic peaks are corresponding to the reduction of
AgO to Ag2O and Ag2O to Ag metal, respectively.
The high reduction current in Fig. 2 indicates the pres-
ence of large active sites on the surface of the n-Ag/
POT/MCPE electrode.
From the above discussions, a scheme pathway for transi-
tions during the potential cycling can be presented as follows:
Anodic transitions:
Ag→Ag OHð Þ2 → Ag2O ð7Þ
Ag→Ag2O→AgO ð8Þ
Cathodic transitions:
AgO→Ag2O ð9Þ
Ag2O→Ag ð10Þ
Fig. 2 Cyclic voltammogram of
n-Ag/POT/MCPE in 0.1 M
NaOH (at =0.1 V s−1
and
E=−0.4 to 0.9 V)
Fig. 3 Typical scanning electron
microscopy (SEM) images of
different electrodes: a bare CPE,
b POT/MCPE, and c, d
n-Ag/POT/MCPE
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7. SEM investigation
Scanning electron micrographs of different electrodes includ-
ing bare CPE, POT/MCPE, and n-Ag/POT/MCPE are shown
in Fig. 3. The morphology for the bare CPE (Fig. 3a) shows
carbon powders enwrapped in paraffin oil and that there are
some holes or cavities on the electrode surface because the
carbon paste is porous. However, more pores on surface to-
pography were observed for POT/MCPE (Fig. 3b). Further-
more, it yields a larger available area and, in the case of intro-
ducing Ag catalyst, with better dispersion. Figure 3c shows
the morphology of the n-Ag/POT/MCPE. According to this
image, the spherical aggregates may be formed through the
settlement of several nanoparticles of Ag. Figure 3d shows the
particle size smaller than 100 nm. Thus, the effective surface
area shows that the presence of the POT gives rise to decrease
Fig. 4 CVs of CPE (a), Ag/MCPE (b), POT/MCPE (c), and n-Ag/POT/
MCPE (d) in 0.1 M NaOH solution in the a absence and b presence of
20 mM hydrazine
Fig. 5 Current–potential curves of n-Ag/POT/MCPE prepared with 1
(a), 2 (b), 3 (c), 4 (d), 5 (e), and 7 mM ( f ) OT (in the presence of
20 mM hydrazine and =20 mV s−1
). Inset: variation of electrocatalytic
peak current of N2H4 oxidation with OT concentration
Fig. 6 Cyclic voltamograms of n-Ag/POT/CPE in 0.1 M NaOH solution
in the presence of 20 mM hydrazine at scan rate of 20 mV s−1
prepared in
5 (a), 7 (b), 10 (c), 12 (d), and 15 (e) cycle numbers of OT polymerization.
Inset: variation of electrocatalytic peak current of N2H4 oxidation with
cycle number
Fig. 7 CVs of n-Ag/POT/MCPE prepared in 5 (a), 10 (b), 15 (c), 20 (d),
25 (e), and 30-minute ( f ) accumulation times in the presence of 20 mM
N2H4 and 0.1 M NaOH solution at =20 mV s−1
. Inset: variation of
electrocatalytic peak current of N2H4 oxidation with accumulation times
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8. the aggregation of the Ag nanoparticles, relatively. So, the
effective surface area of the aggregates is improved. These
results are in agreement with electrochemical experiments.
Electrochemical oxidation of hydrazine
Figure 4 reveals the effect of presence of hydrazine on various
electrodes (containing unmodified and modified electrodes).
In the absence of hydrazine (Fig. 4a), no anodic or cathodic
current was observed, but in the presence of N2H4, the oxida-
tion of hydrazine on unmodified electrode occurs in 0.4 V
(Fig. 4b, a). With modified electrodes, the anodic current
gradually increases and oxidation potential is largely changed,
but this shift for n-Ag/POT/MCPE is greater than n-Ag/
MCPE and POT/MCPE (−0.05, 0.0, and 0.02, respectively).
These results suggested that the accumulation of silver nano-
particles on POT has a positive effect on oxidation potential.
The parameters affecting the electrode modification
The OT concentration effect
The effect of OT monomer concentration (1.0–7.0 mM) dur-
ing the electropolymerization for preparation of the POT/
MCPE films with certain thickness was investigated on reac-
tivity of the modified electrodes for N2H4 oxidation. The ob-
tained results for electrocatalytic peak current in this condition
Fig. 8 Current–potential curves
of n-Ag/POT/MCPE in 0.1 M
NaOH solution containing
hydrazine at various scan rates: 10
(a), 20 (b), 30 (c), 40 (d), 50 (e),
and 60 mV s−1
( f ). (condition =
5.0 mM, 20 cycle numbers, and
20-min accumulation time). Inset
A: variation of electrocatalytic
peak current of N2H4 oxidation
with scan rate. Inset B: variation
of electrocatalytic peak current of
N2H4 oxidation with root square
of scan rate
Fig. 9 The plot of hydrazine oxidation peak potential on the n-Ag/POT/
MCPE electrode versus log v
Fig. 10 Electrochemical responses of n-Ag/POT/MCPE in 0.1 M NaOH
in the 0 (a), 1.0 (b), 2.5 (c), 5 (d), 7.5 (e), 10 ( f ), 15 (g), 20 (h), 30 (i), 40
(j), 50 (k), 60 (l), 70 (m), and 80 mM (n) hydrazine (3.0 mM OT, 5.0 mM
AgNO3 solution at E=−0.4 to 0.1, and =20 mV s−1
). Inset: variation of
electrocatalytic peak current of N2H4 with hydrazine oxidation
concentration
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9. show that there is an increase in the electrooxidation peak
current of hydrazine when there is an increase in the monomer
concentration from 1.0 to about 3.0 mM (Fig. 5). A decrease
in N2H4 electrooxidation current can be observed when the
higher monomer concentrations are used. This may be attrib-
uted to the simultaneous formation of some oligomers during
the polymerization of OT in high concentrations [22]. Thus,
formation of the oligomers affects the morphology of the
polymer which decreases the amount of Ag nanoparticles dis-
persed in the film. It also decreases the effective surface area
of the nanocatalyst.
Effect of cycle number of electropolymerization
on the hydrazine oxidation
Electrochemical polymerization offers the possibility of con-
trolling the thickness and homogeneity of POT film on the
electrode surface. The influence of cycle numbers for prepa-
ration of the POT films on the electrocatalytic oxidation of
N2H4 was investigated, and the corresponding results are
shown in Fig. 6. Under the constant accumulation time of
Ag ions, the anodic peak current rises progressively for cycle
numbers up to 10 cycles and drops afterward. This implies
that the electrocatalysis of hydrazine oxidation is sensitive to
thickness of the polymer film. The increase in the anodic peak
current for cycle numbers up to 10 cycles may be due to the
occupation of Ag nanoparticles in the pores of polymers with
the real sizes. The decrease in anodic peak current for N2H4
oxidation beyond 10 cycles may be due to reducing of real
surface area of Ag hydroxide by the excessive presence of
polymers on the electrode surface.
The effect of accumulation time
In order to incorporate Ag ions at the surface of the electrode,
the freshly prepared POT/MCPE was placed in an aqueous
solution of 5.0 mM AgNO3 in an open circuit for several
minutes. The electrocatalytic oxidation peak currents of
N2H4 increased gradually with increasing of accumulation
times. The maximum value was achieved at 20 min and then
decreased, so 20 min was chosen as the optimum time, which
indicated that saturated accumulation on the n-Ag/POT /
MCNTPE had been achieved (Fig. 7).
The scan rate effect
Cyclic voltammograms of n-Ag/POT/MCPE in the presence
of 20 mM hydrazine at the various scan rates were recorded
(Fig. 8). From this figure, it can be seen that with increasing
Table 1 Comparison of the
efficiency of n-Ag/POT/MCPE
with some of the previously
reported electrodes for N2H4
oxidation in alkaline medium
Electrocatalyst Electrolyte Hydrazine
concentration
(mM)
Scan rate
(mV s−1
)
Peak
potential
(V)
Reference
Au/TiO2-NTs/Ti 0.1 M phosphate
buffer (pH 7.0)
0.85 100 0.23 [32]
Ni(OH)2–MnO2/MGCE 0.1 M phosphate
buffer (pH 7.0)
20 20 0.65 [33]
CuO(H)/MCu 0.1 M phosphate
buffer (pH 7.0)
20 50 0.25 [34]
Ni(II)/BA/MWCNT 0.1 M NaOH 2 50 0.53 [35]
n-Ag/POT/MCPE 0.1 M NaOH 20 20 −0.05 This work
Fig. 11 Chronoamperogram plots of different N2H4 concentrations on
the POT/MCPE: absence (a), 10 (b), 20 (c), 30 (d), 40 (e), and 50 mM ( f )
(condition: 3.0 mM OT, at potential step of 0.05 V and t=20 s)
Fig. 12 Chronoamperogram plots of different N2H4 concentrations on
the n-Ag/POT/MCPE: absence (a), 1.0 (b), 10 (c), 15 (d), 20 (e), 30 ( f ),
40 (g), 50 (h), and 60 mM (i) (condition: 3.0 mM OT and 5.0 mM
AgNO3, at potential step of 0.05 V and t=20 s). Inset: variation of
N2H4 oxidation current with N2H4 concentration
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10. the potential scan rate, the peak potential for catalytic oxida-
tion of hydrazine shifts to positive potentials (Fig. 8a). This
clear shift of the peak potential occurred as expected for irre-
versible electrochemical reactions [31]. The obtained cyclic
voltammograms were used to examine the variation of oxida-
tion peak current versus scan rate. The oxidation current of
hydrazine increased linearly with the square root of scan rate
on n-Ag/POT/MCPE (Fig. 8c), suggesting that the reaction is
diffusion control limited.
In order to get the information on the rate-determining step,
Tafel slope, b, was determined using the following equation
valid for a totally irreversible diffusion controlled process
[31]:
Ep ¼ 0:5b log υ þ constant ð11Þ
where b is the Tafel slope and v is the scan rate; the Tafel slope
can also be expressed as
b ¼ 2:3 R T αn Fð Þ−1
ð12Þ
On the basis of these equations, the slope of the plots of Ep
versus log is b/2 which was found equal to 0.137 in this work
(Fig. 9), so b=0.274 V. These slope values indicate a transfer
coefficient equal to 0.25.
The effect of hydrazine concentration
Cyclic voltammetric responses of the n-Ag/POT/MCPE in
0.1 M NaOH solution containing different hydrazine concen-
trations are presented in Fig. 10. It can be seen, upon the
addition of hydrazine, that an enhancement in the anodic cur-
rent was created.
From the CV profile in the absence of hydrazine (Fig. 10,
a) and those in the presence of hydrazine (b–n), it is found that
an enhancement in the anodic current commences at the po-
tential of −0.34 V, showing the high capability of Ag nano-
particles for oxidation of hydrazine in alkaline solution as
shown in reaction (1).
Fig. 13 Plot of I versus
t−1/2
obtained from
chronoamperometric experiments
of n-Ag/POT/MCPE in 0.1 M
NaOH solution containing
different concentrations of
hydrazine: 1.0, 10, 15, 20, 30, 40,
50, and 60 mM, respectively
Fig. 14 a Chronoamperometric
response for the n-Ag/POT/
MCPE in the 0.1 M NaOH+
20 mM N2H4 solution at potential
step of 0.05 (t=600 s). b The
chronoamperograms of
n-Ag/POT/MCPE in the 0.1 M
NaOH+20 mM N2H4: after
preparation of modified electrode
(a) and after 5 days (b)
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11. These results show that the prepared n-Ag/POT/MCPE
presents high electroactivity toward the hydrazine oxidation.
Plot of the anodic peak current (Ip) versus added hydrazine
concentrations is shown in insets of Fig. 10 where a well linear
relationship (R2
=0.9914) appears from 1.0 to 50 mM. Also,
Table 1 lists the peak potential shift of some modified elec-
trodes. As can be seen, the prepared electrode presented low
peak potential for the hydrazine oxidation comparison to some
of the previously reported electrodes.
Chronoamperometric investigation
Chronoamperometric study of hydrazine oxidation
on the n-Ag/POT/MCPE
Chronoamperometry (CHA) was used for the hydrazine oxi-
dation at a fixed potential of 0.05 V. Effect of the hydrazine
concentration on chronoamperograms for the POT/MCPE and
n-Ag/POT/MCPE at a potential step of 0.05 V is shown in
Figs. 11 and 12. At this potential, in the absence of hydrazine,
no anodic or cathodic current was observed. With the addition
of hydrazine, there are increases in the anodic currents for
modified electrodes, but this increment for n-Ag/POT/MCPE
is greater than for POT/MCPE (Figs. 11 and 12). These results
shows that chronoamperograms are in good agreement with
cyclic voltammograms. So the ability of Ag nanoparticles in
the improvement of hydrazine oxidation in alkaline media was
demonstrated again.
As can be seen in Fig. 12, an increase in the concentration
of N2H4 from 1.0 to 40 mM caused a linear increase in the
steady state current (R2
=0.9908). The oxidation reaction of
hydrazine results in the visible evolution of N2 gas on the
surfaces of the n-Ag/POT/MCPE and POT/MCPE. Therefore,
the current oscillation at up to 30 mM hydrazine could be
ascribed to the bubbling of N2 gas through the reaction (1).
In order to get more information about the electrocatalytic
process, chronoamperometry was used to evaluate the diffu-
sion coefficient of hydrazine. Chronoamperometric measure-
ments were carried out at different concentrations of hydrazine
on the n-Ag/POT/MCPE by setting the working electrode
potential at 0.05 V. The diffusion coefficient was obtained
according to the Cottrell equation [31]:
I ¼ nFACD
1
.
2
π
−1
.
2
t
−1
.
2
ð13Þ
where n, A, D, and C are the number of electrons (n=4),
geometrical surface area (0.152 cm2
), diffusion coefficient
(cm2
/s), and bulk concentrations (mol/cm3
) of hydrazine, re-
spectively. I is the current controlled by the diffusion of hy-
drazine from the bulk solution to the electrode/solution inter-
face. From the slope of the plot (Fig. 13), the D of hydrazine
was calculated as 2×10−7
cm2
/s.
Stability of the n-Ag/POT/MCPE
Different aspects regarding the stability of the n-Ag/POT/
MCPE were investigated. The long-term stability of modified
electrode was examined by using CHA technique. Figure 14
presents current–time plots for hydrazine oxidation at the n-
Ag/POT/MCPE in 0.1 M NaOH in the presence of 20 mM
N2H4. To evaluate the activity and stability of the n-Ag/POT/
MCPE, chronoamperogram was recorded for a large time win-
dow in the presence of N2H4. It is obvious that the n-Ag/POT/
MCPE exhibits a good stability toward N2H4 oxidation. Also,
the signal responses of the modified electrode were recorded
and studied in a few days. After 5 days, the n-Ag/POT/MCPE
yielded 82 % of the original response.
Conclusion
Silver nanoparticles were deposited on the surface of POT
modified carbon paste electrode using the electrochemical
method. The SEM investigation showed a larger available
area and better dispersion of silver nanoparticles on modified
electrode. Electrooxidation of hydrazine on the n-Ag/POT/
MCPE takes place at −0.05 V while the peak potential of
hydrazine oxidation on the unmodified electrode is 0.4 V.
The cyclic voltammogram and chronoamperometric study
showed an increase in oxidation current with addition of hy-
drazine concentration. Our work showed that nanosilver is a
stable substrate which provides excellent activity for oxidation
of hydrazine. The high electroactivity of the n-Ag/POT/
MCPE could be related to its large surface area. Finally, the
preparation of this modified electrode is cheap, simple, and
affordable by considering the economy.
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