Decoration of silver nanoparticles on activated graphite substrate and their electrocatalytic activity for methanol oxidation

Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

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Journal of Science: Advanced Materials and Devices
journal homepage: www.elsevier.com/locate/jsamd

Original Article

Decoration of silver nanoparticles on activated graphite substrate and
their electrocatalytic activity for methanol oxidation
M.S. Shivakumar a, G. Krishnamurthy b, **, C.R. Ravikumar c, *, Aarti S. Bhatt d
a

Research Centre, Dept. of Chemistry, ACS College of Engineering, Bangalore, 560074, India
DOS in Chemistry, Bangalore University, Bangalore, 560001, India
c
Dept. of Chemistry, East West Institute of Technology, Bangalore, 560091, India
d
Department of Chemistry, NMAM Institute of Technology, Nitte, 574110, India
b

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 21 December 2018
Received in revised form
31 May 2019
Accepted 3 June 2019

Available online 10 June 2019

Silver nanoparticles (~30e70 nm) have been impregnated on the activated graphite powder by an
electroless plating method. The so prepared silver decorated graphite powders are characterized by field
emission scanning electron microscopy, powder X-ray diffraction, energy dispersive X-ray and X-ray
photoelectron spectroscopy. The activated graphite powder displays a high surface coverage with tin
which is essential, as this ensures a thorough and complete coating of the graphite powder with silver.
The electrochemical studies of Graphite, Sn/Graphite and successive decoration of AgeSn/Graphite
powder have been carried out using cyclic voltammetry in the potential range between À1.2 and 0.0 V at
a sweep rate of 50 mV sÀ1 and their electrocatalytic activity for methanol oxidation has been examined in
alkaline medium. The effective active surface area of Graphite and AgeSn/Graphite electrode are
calculated to be 6.2479 Â 10À5 cm2 and 6.7886 Â 10À5 cm2, respectively. The impedance spectrum of the
AgeSn/Graphite electrode displays a depressed semicircle in the high-frequency region which corresponds to low charge resistance and high capacitance. The results highlight the electrocatalytic behavior
of the graphite supported silver nanoparticles, making them suitable for fuel cell applications.
© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
Keywords:
Silver nanoparticles
Electro catalyst
Graphite powder
Electroless deposition
Methanol oxidation

1. Introduction
Electroless deposition of silver nanoparticles on various substrates is a well-known technique, which generally employed for
this metal. This method involves pretreatment of the substrate
surface, sensitization and activation for increasing the rate of
metal ions reduction on the surface of carbon substrate [1e3].
The applications of silver nanoparticles (Ag NPs) thus obtained
according to their properties like electric conductivity, reflectivity and other surface properties such as their ability to absorb

as well as chemisorb, making them suitable candidates for
catalysis applications [4e8]. These properties also lend them
unique biological, chemical and physical properties matching up
to their macro-scaled counterparts. No wonder, Ag NPs have also

* Corresponding author.
** Corresponding author.
E-mail addresses: (G. Krishnamurthy), Ravicr128@
gmail.com (C.R. Ravikumar).
Peer review under responsibility of Vietnam National University, Hanoi.

been used in varied fields such as renewable energies, medicine
and environment [9,10].
An alternative for the reduction of silver nanoparticles is to
introduce organic functional groups, for instance, carboxyl and
hydroxyl groups onto the carbon surface [11,12]. These organic
functional groups act as binding sites to the metal ions which undergo reduction to ultimately form a metal layer on the carbon
surface [13,14]. Carbon materials such as graphite are widely used
in industries and processing techniques due to their high conductivity and elevated specific surface area. Also, the low cost of
graphite adds to its preferences [15].
Electrocatalysts are generally employed in fuel cells as it helps in
improving the fuel oxidation. However, the high cost of fuel cells
and its low durability hinders its wide application. In order to make
these fuel cells affordable, research is being carried out to decrease
the cost by decreasing the amount of expensive elements used or
by substituting some of the expensive components with cheaper
but more durable materials. Simultaneously, an effort is being made
to improvise its durability by developing high durable catalyst
supports or it can also be done by using Pt alloys as electro catalysts
[16]. Carbon based materials make a better catalyst support; for

/>2468-2179/© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
( />

M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

instance XC-72 Vulcan carbon powder is a widely used support in
the electrodes of several modern fuel cells. The graphite submicron
particles on the catalyst support aids in the oxidation of fuel cells
application.
Our present work employs the electroless plating method to
reduce silver nanoparticles by introducing organic functional
groups on the activated graphite powder with electrocatalytic
surfaces. This serves as a better platform to obtain decorated silver
nanoparticles on sensitized and activated graphite powders. The
oxidized graphite powders have been treated with reducing agent
and immersed in Ag bath solution (pH 11) to obtain silver nanoparticles on graphite powders [17]. The so-prepared decorated
silver nanoparticles on sensitized and activated graphite have been
tested for their electrocatalytic activity of methanol oxidation in
alkaline solution by cyclic voltammetry (CV) and electrochemical
impedance spectroscopy (EIS). The surface morphology, structure,
composition have been characterized by Field emission scanning
electron microscopy (FESEM), Energy dispersive X-ray analysis
(EDX), powder X-ray diffraction (PXRD) and X-Ray photoelectron
spectroscopy (XPES).

291

coating and the extent of coverage were analyzed using a Carl Zeiss
Ultra 55 FESEM. The elemental analysis was done using Axis Ultra

X-Ray Photoelectron spectroscopy. The electrochemical studies
were carried out using an Auto lab PGSTAT30 model with pilot
integration controlled by GPES 4.9 software in a threecompartment cell. The measurements were carried in the frequency range of 1 Hz to 1 MHz. The experimentally obtained
real and imaginary components were analyzed using the CH608E
instrument.
2.4. Preparation of working electrode
For the preparation of carbon paste electrode, 500 mg of silver
decorated graphite powder was thoroughly mixed with 20% of
silicone oil. The resulting paste was packed into a Teflon tube and a
copper wire was inserted for external electric contact. The surface
was polished by butter paper. When necessary, a fresh surface was
obtained by pushing an excess and polishing the electrode surface
mechanically using steel rod.
3. Results and discussion

2. Materials and methods
3.1. The mechanism of Ag deposition on Sn/graphite
All the chemicals have been procured from SigmaeAldrich and
have been used without any further purification. Graphite powder,
silver nitrate, stannous chloride, polyethylene glycol, glucose, potassium hydroxide and methanol used have !99.99% purity. The
solvents sulphuric acid, nitric acid and aqueous ammonium hydroxide solution are of AR grade.
2.1. Functionalization of graphite powder
About 1 g of graphite powder was treated in 200 cm3 of an acid
mixture of conc. HNO3 and conc. H2SO4 (1:3 v/v) and refluxed at
110  C for 8 h to produce eOH and eCOOH functionalized graphite
powder. The samples were then filtered, washed with distilled
water and dried at 95 ± 3  C for about 6 h. Thus, the functionalized
graphite powder was obtained.

The mechanism of deposition of silver on graphite substrate

involves, firstly, the sensitization of graphite surface in the SnCl2
solution to enhance the absorption of silver ions in the subsequent
activation process. The stannous ions adsorbed on to the surface of
functionalized graphite surface during sensitization act as seeds for
the nuclei of the Ag nanoparticles growth during activation process.
The initial formation of the silver nanoparticles is based on the
application of reducing and oxidizing agents on the graphite substrate surface, namely Sn2þand Agþ. This redox reaction proceeds as
[8,18e20].

Sn2þ þ 2Agþ /Sn4þ þ 2Ag

(1)

In this method, which is a form of polyol method, ethylene
glycol acts as a reducing agent. Silver nanoparticles are synthesized
during the reduction of silver ions while the hydroxyl groups of
poly (ethylene glycol) are oxidized to aldehyde groups.

2.2. Decoration of silver nanoparticles on graphite powder
To obtain decorated silver nanoparticles on graphite by electroless plating, 2 g of oxidized graphite powder (<20 mm) was
treated with 50 cm3 of 20% SnCl2, stirred for 10 min and then
filtered. The obtained graphite powder was then treated with
30 cm3 of glucose solution, 20 cm3 of methanol and 1 g of polyethylene glycol, stirred for 10 min, filtered and transferred to a
250 cm3of silver bath solution (3 g of AgNO3 in 250 cm3 of water)
along with 0.6 g NaOH. To this, ammonia solution was added
dropwise to get a clear solution, stirred for 45 min, filtered and
dried [17].

2AgNO3 þ 2NaOH /Ag2 OðsÞ þ 2NaNO3 þ H2 O

(2)

Ag2 OðsÞ / 2Agþ þ O2À

(3)

HOCH2 CH2 OH / CH3 CHO þ H2 O

(4)

CH3 CHOðaqÞ þ 3OHÀ /CH3 CHOOÀ þ 2H2 O þ 2e

(5)

Agþ þ e/Ag0

(6)

Ag2 OðSÞ þ 4NH3 ðaqÞ þ 2NaNO3 ðaqÞ þ H2 O/2AgðNH3 Þ2 NO3 ðaqÞ þ 2NaOH

(7)

2.3. Characterization
The samples were characterized by powder X-ray diffraction
studies using a high-resolution X-ray diffractometer (Shimadzu
7000S) at a scanning rate of 2 minÀ1 using CuKa radiation. It was
operated at 45 kV and 40 mA. The surface morphology of the metal

2AgðNH3 Þ2 NO3 ðaqÞ þ CH3 CHO /2Ag0 þ CH3 COOH þ 4NH3
þ HNO 3

(8)


292

M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

The above equations (eqs. (2)e(8)) depict the possible proposed
mechanism of the in situ synthesis of silver nanoparticles under alkali
conditions. On coming in contact with the alkali solution, silver nitrate
gets converted to anhydrated Agþ; a reaction between OHÀ ions with
silver ions leads to the formation of silver oxide (Ag2O). In presence of
a highly alkaline environment (pH 13), Ag2O dissociates into silver
ions bonded to the hydroxyl and carboxylate moieties on the surfaces
of graphite through ionic interactions (eq. (1)).
Simultaneously, polyethylene glycol undergoes alkaline hydrolysis to produce aldehyde which oxidizes releasing electrons.
As a result, silver ions reduce to silver nanoparticles, resulting in
a transparent clear solution (eq. (5)À(8)). Similar to silver ions,
the resulting silver nanoparticles also remain bonded onto the
graphite surface. Finally, a nano layer of silver nanoparticles is
deposited on the graphite surface by treating it with alkali in
presence of ammonia solution. As shown in equation (2), silver
nitrate in presence of alkali oxidizes to silver oxide, leading to
the formation of Agþ ions. Some of the Agþ ions produced are
reduced to Ag0 whereas the remaining form a diammine silver
(I) complex on addition of ammonia; the complex so formed is
Tollen's reagent. Tollen's reagent is a commonly used source to
synthesize silver nanoparticles, as it readily undergoes reduction
to form Ag0 in presence of aldehyde which in turn oxidizes to
carboxyl group. Being positively charged, [Ag(NH3)2]þalso gets

easily absorbed onto the graphite surface via eCOOÀ and eOH
functional groups [21e23].
3.2. Powder X-ray diffraction studies
The diffraction pattern of the silver decorated graphite powder
was studied on a PXRD. From Fig. 1(a) it can be seen that PXRD

patterns of graphite showed very strong peaks at 2q of 26.66 and
54.81 which matches very well with that of graphite powder.
The PXRD also exhibited diffraction peaks at 38.26 , 44.23 , 64.8 ,
74.7 and 76.6 corresponding to (111), (200), (220), (222) and
(311) planes of silver as well as diffraction peaks at27.7, 32.46 ,
57 and 67.8 for tin. The average crystallite size (D) of nanoparticles was estimated from diffraction planes along the direction normal to the (h k l) plane applying Scherrer's formula and
was found to be around 34 nm. The PXRD peaks further
confirmed the crystalline nature of silver nanoparticles [24], this
indicates a uniform and good decoration of silver nanoparticles on
graphite.
3.3. Energy dispersive X-ray analysis
EDX analysis was carried out to confirm the deposition of silver
on the graphite layer. This is evident from Fig. 1(b) which displays
the EDX pattern of silver deposited graphite powder. The figure
clearly hows prominent peaks corresponding to silver and tin along
with the carbon peak.
3.4. Field emission scanning electron microscopy
The surface morphology of the silver coating and uniformity
in distribution were analyzed by a FESEM. Fig. 2 shows the images of as obtained silver nanoparticles deposited graphite
powder. The powder seems to have a rod like structure and the
average size of the silver nanoparticles on the surface of activated graphite is approximately in the range between 30 and
70 nm. This agrees well with the crystallite size calculated via
PXRD in section 3.2.

Fig. 1. (a) PXRD pattern of silver deposited graphite powder. (b) EDX Spectrum of silver deposited Graphite powder (Inset).


M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

293

Fig. 2. FESEM images of silver nanoparticles deposited on Graphite powder: (a) 5000 X and (b) 50,000 X.

3.5. X-ray photoelectron spectroscopy

3.6. Electrochemical characterization of electrode

Fig. 3 shows the wide angle spectra for silver deposited on
graphite powder and also the individual binding energy spectrum
of silver, tin and carbon. The Ag3d5/2 and Ag3d3/2 peaks at 367.5 eV
and 373 eV are attributed to silver. The peaks at 486.5 eV and
495 eV correspond to tin and the peak at 284.2 eV corresponds to
carbon 1Cs of graphite. The characteristic XPES spectrum with
appropriate binding energies and intensities further confirmed the
deposition of silver and tin on graphite [25e27].

3.6.1. Cyclic voltammetry studies
Fig. 4(a) represents the CV for the AgeSn/Graphite carbon paste
electrode in 0.5M KOH with increasingly varying methanol concentrations such as 0.025e1 M. During the course of the study, the
CV exhibited a significant change in its response and also anodic
peak current (Ipa) value for methanol oxidation. The values are
tabulated in Table 1. It can be observed that in the presence of
CH3OH anodic peak current appears at À0.75 V, which is in

(a)

160000

(b)

284.2eV

2500

Intensity(cps)

120000

Intensity(cps)

Carbon

3000

80000

40000

2000
1500
1000
500

0

0

8000

200

Tin

600

800

1000

0
275

1200

(c)

486.5eV

8000

495.2eV

Intensity(cps)

6000

Intensity(cps)

400

Binding Energy(eV)

4000

280

Silver

285

290

295

Binding Energy(eV)
367.5eV

300

(d)

373.6eV

6000

4000

2000

2000
0

480

490
500
Binding Energy(eV)

510

355

360

365

370

375

Binding Energy(eV)

380

Fig. 3. XPES spectra: (a) Wide angle spectrum of silver deposited on Graphite powder, (b) Carbon, (c) Tin and (d) Silver on Graphite powder.

M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

1.0x10

-4

5.0x10

-5

Ag-Sn/Graphite electrode

4.0x10

(a)

0.0
-5.0x10

-5

-1.0x10

-4

-1.5x10

-4

1 M CH3OH

-2.0x10

-4

0.025 M CH3OH

0.025 M CH3OH
0.05 M CH3OH
0.07 M CH3OH

-1.2

-1.0

-0.8

-0.6

-3

1M CH3OH + 0.5 M KOH

2.0x10

1 M CH3OH

-0.4

Current (A)

-4

1.0x10

-4

(c)

0.0

0.1 M CH3OH

(a)

(b)

-3

-0.2

0.0

-1.5

Potential (V)
2.0x10

(b)

Graphite (a)
Sn/Graphite (b)
Ag-Sn/Graphite (c)

Current (A)

Current (A)

294

-1.0

-0.5

Ag-Sn/Graphite electrode in 1M MeOH+0.5M KOH

0.0

0.5

Potential (V)

1.0

1.5

(c)

0.0

-1.0x10

-4

-2.0x10

-4

-3.0x10

-4

250 mV S

10 mV S
-1.2

-1.0

-0.8

-0.6

-0.4

Potential (V)

10 mv/s

20m v/s
50 mv/s
100 mv/s
150 mv/s
200 mv/s
250 mv/s

-1

-1

-0.2

0.0

Fig. 4. (a). Cyclic voltammogram of AgeSn/Graphite electrode in different concentration methanol in 0.5M KOH. (b). Cyclic voltammogram of Graphite (a), Sn/Graphite (b) and
AgeSn/Graphite (c) in 1 M CH3OH containing 0.5 M KOH at the sweep rate of 50 mV/s. (c). Cyclic voltammogram of AgeSn/Graphite electrode in a mixture of 1MCH3OHþ0.5M KOH
solution at different scan rates (10, 20, 30, 50,100, 150, 200 and 250 mV/s).

Table 1
Electrocatalytic activity of AgeSn/Graphite electrode at different concentrations of methanol in 0.5 M KOH.
Concentration of CH3OH (M)

Epa(V)

Ipa (A)

0.025
0.05
0.07

0.1
1

À0.76
À0.77
À0.76
À0.76
À0.75

4.595
5.545
7.329
8.154
9.814

accordance with the oxidation of CH3OH at crystalline Ag NPs. With
an increase in the methanol concentration, the peak response increases initially up to 1M methanol, followed by a decrease in the
peak response. It is also noteworthy that above 1 M of methanol
concentration, the oxidation current decreases. This is probably due

Â
Â
Â
Â
Â

10À5
10À5
10À5
10À5

10À5

Epc(V)

Ipc (A)

À0.8319
À0.8355
À0.9179
À0.9628
À0.9291

À9.025
À1.081
À1.388
À1.377
À1.554

Â
Â
Â
Â
Â

10À5
10À4
10À4
10À4
10À4

to the adsorption of methanol molecules on the electrocatalyst
leading to the blockage of active sites [28].
If we examine the electrocatalyst performance (Table 2), for all
the three systems the onset potential for CH3OH oxidation remains
constant. However, anodic peak current and anodic peak potential

Table 2
Comparative electrochemical performance of methanol oxidation on Graphite (a), Sn/Graphite (b) and AgeSn/Graphite (c) electrode measured in a solution of 1M CH3OH in
0.5M KOH at a sweep rate of 50 mV/s.
Electrocatalytic Performance Data
Electrodes
Graphite (a)
Sn/Graphite (b)
AgeSn/Graphite (c)

If(A)
À4

À1.549 Â 10
À1.096 Â 10À4
9.698 Â 10À5

Eonset(V)

Epa(V)

À0.71 ± 0.04
À0.71 ± 0.04
À0.71 ± 0.04

À0.71
À0.74
À0.75


M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

(Epc) values vary; with the AgeSn/Graphite being the most favorable catalyst system. It displays a higher current density when
compared to the other intermediate states (Sn/Graphite and
Graphite) as shown in Fig. 4(b).
The silver nanoparticles on graphite are thus capable of catalyzing the oxidation of methanol. The first step of the oxidation is
the adsorption of methanol on the surface of Ag NPs acting as
catalyst. This results in a step by step removal of hydrogen in the
form of hydrogen cations to finally form a silver-carbon residue.
The latter reacts with dissociated water to finally release carbon
dioxide. In the process, along with the removal of each hydrogen
ion, an electron gets released giving rise to methanol oxidation
current. The mechanism can be understood by the following reactions [16,29].

CH3 OH þ H2 /CO2 þ 6Hþ þ 6e

(9)

CH3 OH þ Ag/Ag À CH2 OH þ Hþ þ e

(10)

Ag À CH2 OH þ Ag/Ag2 À CHOH þ Hþ þ e

(11)

Ag2 À CHOH þ Ag/Ag3 À COH þ Hþ þ e

(12)

Ag3 À COH /Ag À CO þ 2AgðsÞ þ Hþ þ e

(13)

H2 O / OHÀ þ Hþ

(14)

Ag À CO þ OHÀ /AgðsÞ þ CO2 þ Hþ þ e

(15)

Fig. 4(c) represents the cyclic voltammogram, corresponding
to AgeSn/Graphite electrode in 1M CH3OH in 0.5M KOH solution
at various scan rates (v ¼ 10e250 mV/s). In the present case, the

Current (A)

2+

1.0x10

-3

5.0x10

-4

G raphite electrode in 10 m M of Fe /Fe

3+

in 0.5 M KCl

(a)

0.0
-5.0x10

-4

-1.0x10

-3

295

100 m V/S

10 m V/S
0.1

0.2

0.3

0.4

0.5

10mV/S
20mV/S
30mV/S
40mV/S
50mV/S
60mV/S
70mV/S
80mV/S
90mV/S
100mV/S

0.6

Current (A)

Potential (V)
4.0x10

-4

2.0x10

-4

2+

Ag-Sn/Graphite electrode in 10 mM of Fe /Fe

3+

in 0.5 M KCl

(b)

0.0
-2.0x10

-4

-4.0x10

-4

-6.0x10

-4

10mV/S
20mV/S
30mV/S
40mV/S
50mV/S
60mV/S
70mV/S
80mV/S

90mV/S
100mV/S

100 m V/S
10 m V/S
0.1

0.2

0.3

0.4

0.5

0.6

Potential (V)
Fig. 5. Cyclic voltammogram of (a) Graphite and (b) AgeSn/Graphite electrode in a mixture of 5 mM of Fe2þ and Fe3þ in 0.5M KCl solution at different scan rates (10, 20, 30, 40, 50,
60, 70, 80, 90 and 100 mV/s).


296

M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298
-4

2.0x10

Ag-Sn/Graphite Electrode in 1M CH3OH + 0.5 M KOH

-4

Current (A)

1.0x10

0.0

-4

-1.0x10

0

23 C
0
30 C
0
40 C
0
50 C
0
60 C

0

60 C
-4

-2.0x10

0

23 C
-4

-3.0x10

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Potential (V)
Fig. 6. Effect of temperature on cyclic voltammogram of methanol oxidation on of AgeSn/Graphite electrode in the temperature range of 25  Ce60  C with a potential sweep rate of
50 mV sÀ1.

Ipa showed an increase while the cathodic peak current (Ipc)
decreased. The peak currents are proportional to the sweep rate,
indicating that the surface reaction of the electrode is confined.

Cyclic voltammogram of different sweep rates were performed
with Graphite and AgeSn/Graphite carbon paste electrodes in the
ferro/ferri system [30]. From the cyclic voltammogram of Graphite

Fig. 7. Nyquist plots of (a) Graphite (b) Sn/Graphite and (c) AgeSn/Graphite electrode in 5 mM of K3Fe(CN)6 and 0.5M KCl solution and equivalent circuit of electrodes (Inset).


M.S. Shivakumar et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 290e298

and AgeSn/Graphite carbon paste electrodes (Fig. 4(b)), the active
surface area of Graphite and AgeSn/Graphite was estimated using
the RandleseSevecik equation of a reversible process [31].
3

1

(16)

where Ip is the peak current of active surface area, D is diffusion
coefficient, C0 is concentration of electro active species, A is
active surface area, n is number of electrons involved in the reaction and n is sweep rate. The active surface area of Graphite
and AgeSn/Graphite was calculated to be 6.2479 Â 10À5 cm2 and
6.7886 Â 10À5 cm2, respectively. On plotting Ipa as a function of
sweep rate, a linear graph was obtained. The linearity was more
profound in the scan rate range from 10 to 100 mV/s (Fig. 5). The
correlation coefficient (r2) of AgeSn/Graphite was calculated to
be 0.99. The results clearly suggest an adsorption-controlled
process [32].
The temperature dependence on oxidation of 1M methanol in
0.5M KOH, on AgeSn/Graphite electrode was investigated in the

temperature range of 23e60  C by cyclic voltammetry (Fig. 6). In
this temperature range, the shift in the current and potential of
methanol oxidation is not drastic. Nevertheless, it does suggest a
definite kinetic enhancement with increase in temperature from 23
to 60  C [30].
3.6.2. Electrochemical impedance studies
EIS is employed to study the electron transfer between the
electrode surface and electrolyte. The impedance spectra for the
AgeSn/Graphite, Sn/Graphite and graphite electrodes system are
represented in Fig. 7. For the impedance measurement, all electrodes were immersed in 5 mM of [Fe(CN)6]3À/4À and 0.5 M KCl
solution. The analysis was carried out in the frequency range 1 Hz to
1 MHz [33,34]. The electroactivity is governed by the following
equation.

Ã4À

/ ½FeðCNÞ6

i3À

þe

(17)

From Fig. 7 it can be observed that the impedance plot of the
AgeSn/Graphite electrode displays a depressed semicircle for
charge transfer resistance in the high-frequency region, while a
slope related to Warburg impedance in the low-frequency region.
The low impedance of AgeSn/Graphite electrode implies a lower
charge transfer resistance, suggesting an easy electrochemical reaction on this electrode [35e37]. Fig. 7 also gives the equivalent

circuit of the system in the inset; wherein W is the Warburg
impedance at lower frequency range, which is in series with the
charge transfer resistance (Rct) and parallel to capacitance (C). The
order of charge transfer resistance and corresponding capacitance
for Graphite, Sn/Graphite and AgeSn/Graphite electrodes have
been obtained by fitting experimental data according to the
equivalent circuit [38] and tabulated in Table 3. It can be observed
from the values that a minimum Rct and maximum Cdl is obtained
for AgeSn/Graphite electrode. The following result can be summarized from the experiment: Graphite (2.198 Â 10À8 F) > Sn/
Graphite (1.498 Â 10À10 F) < AgeSn/Graphite (6.659 Â 10À7 F). This
Table 3
The electrochemical impedance data of graphite (a), Sn/Graphite (b) and AgeSn/
Graphite (c) electrodes in a 10 mM K3Fe(CN)6 and 0.5 M KCl solution at a sweep
50 mV/s.
Electrodes
Graphite (a)
Sn/Graphite (b)
AgeSn/Graphite (c)

Rs/U
13.29
0.001
31.66

Rct/U
1011.19
3523.2
64.8

indicates that AgeSn/Graphite electrode show better electrocatalytic activity when compared to Sn/Graphite electrode.

4. Conclusion

1

Ip ¼ 2:69 Â 105 Â n2 Â A Â D2 Â C0 Â v2

½FeðCNÞ6

297

Cdl/F

W
À8

2.198 Â 10
1.498 Â 10À10
6.659 Â 10À7

0.1604 Â 10À2
0.3918 Â 10À3
0.6467 Â 10À3

In this report, we have successfully prepared an efficient electrocatalyst by electroless deposition of silver nanoparticles on
activated graphite powder. The analytical techniques such as
FESEM, PXRD, EDX, and XPES have helped us to substantially infer
the supporting data. The electrochemical studies of oxidation of
methanol in alkaline medium were carried out using CV, while the
active surface area of Graphite and AgeSn/Graphite electrodes
were calculated using RandleseSevecik equation. The capacitance

improved and the charge transfer resistance decreased for AgeSn/
Graphite electrode as compared to Sn/Graphite electrode. This indicates a superior surface catalytic activity of AgeSn/Graphite
electrodes. The obtained results are encouraging as the prepared
graphite supported silver nanoparticles have the potential to
deliver as an efficient electrocatalyst for fuel cell applications.
Acknowledgements
The authors acknowledge the instrumental facilities of PXRD
and CV at the Department of Chemistry, Central College, Bangalore
University and EIS facility at Rajarajeshwari College of Engineering,
Research Centre, Department of Chemistry, Bangalore. The authors
would also like to extend their acknowledgement to Indian Institute of Science, Bangalore for providing XPES, FESEM and EDX
facilities.
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