Modification of a glassy carbon electrode with gold-platinum core-shell nanoparticles by electroless deposition and their electrocatalytic activity

Article abstract of DOI:10.1039/c5ra06537b

Gold-platinum (Au@Pt) nanoparticles with a core-shell structure were fabricated on a glassy carbon electrode (GCE) by an electroless deposition method. Initially, gold nanoparticles (AuNPs) were deposited on GCE by reducing HAuCl₄ with NH₂OH. SEM studies showed that the size of the deposited AuNPs was found to be 30 nm. The deposited AuNPs on GCE act as the nucleation centre for the deposition of platinum nanoparticles (PtNPs) in the presence of H₂PtCl₆ and NH₂OH. The size of the PtNP increases on increasing the electroless deposition time. The SEM studies demonstrated that the electroless deposition of Pt on Au was isotropic and uniform. Further, Au@Pt modified substrates were characterized by X-ray photoelectron spectroscopy (XPS), an X-ray diffraction method (XRD), energy dispersive X-ray analysis (EDAX) and cyclic voltammetry (CV). XPS showed characteristic binding energies at 71.2 and 74.4 eV for PtNPs and 83.6 and 87.3 eV for AuNPs indicating the zero valent nature of both Au and Pt. Further, the electrocatalytic activity of the Au@Pt modified electrode was examined by studying the reduction of dioxygen and oxidation of hydrazine. The modified electrode showed higher electrocatalytic activity towards the oxidation of hydrazine not only by shifting its oxidation potential towards a less positive potential but also enhancing the oxidation peak current. It also exhibited higher electrocatalytic activity towards the reduction of dioxygen by shifting its reduction overpotential by 650 mV towards a less positive potential when compared to bare GCE.

Full text of DOI:10.1039/c5ra06537b

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: N.S.K Gowthaman
and S. A. John, RSC Adv., 2015, DOI: 10.1039/C5RA06537B.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
Journal Name
RSCPublishing
ARTICLE
Modification of Glassy Carbon Electrode with Goldꢀ
Platinum CoreꢀShell Nanoparticles by Electroless
Deposition and Their Electrocatalytic Activity
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
N.S.K. Gowthaman and S. Abraham John*
DOI: 10.1039/x0xx00000x
Goldꢀplatinum (Au@Pt) nanoparticles with coreꢀshell structure were fabricated on glassy carbon electrode
(GCE) by electroless deposition method. Initially, gold nanoparticles (AuNPs) were deposited on GCE by
reducing HAuCl4 with NH2OH. SEM studies showed that the size of the deposited AuNPs was found to
be 30 nm. The deposited AuNPs on GCE act as the nucleation centre for the deposition of platinum
nanoparticles (PtNPs) in the presence of H2PtCl6 and NH2OH. The size of the PtNP increases while
increasing the electroless deposition time. The SEM studies demonstrated that the electroless deposition
of Pt on Au was isotropic and uniform. Further, Au@Pt modified substrates were characterized by Xꢀray
photoelectron spectroscopy (XPS), Xꢀray diffraction method (XRD), energy dispersive Xꢀray analysis
(EDAX) and cyclic voltammetry (CV). XPS showed characteristic binding energies at 71.2 and 74.4 eV
for PtNPs and 83.6 and 87.3 eV for AuNPs indicating the zero valent nature of both Au and Pt. Further,
the electrocatalytic activity of Au@Pt modified electrode was examined by studying the reduction of
dioxygen and oxidation of hydrazine. The modified electrode showed higher electrocatalytic activity
towards the oxidation of hydrazine not only by shifting its oxidation potential towards less positive
potential but also enhanced the oxidation peak current. It also exhibited higher electrocatalytic activity
towards the reduction of dioxygen by shifting its reduction overpotential by 650 mV towards less positive
potential when compared to bare GCE.
www.rsc.org/
and solꢀgel synthesis.13ꢀ16 However, these bimetallic NPs are
often synthesized in the form of colloidal dispersion or matrix
Introduction
The field of heterogeneous catalysis using bimetallic
nanoparticles as catalysts received great interest in recent years
because they offer increased catalytic activity with enhanced
stability as compared to their monometallic counterparts.1ꢀ3 It
has been well established that bimetallic NPs often show novel
properties that are not exhibited by either of the monometallic
NP.4,5 However, it is difficult to tune the electronic and
chemical properties of particular bimetallic NPs relative to the
respective monometallic NP. For this reason, the study of
bimetallic NPs in the field of catalysis has gained considerable
interest. However, it is a paramount task for the researchers to
prepare bimetallic NPs with excellent electronic and chemical
properties that differ from their individual counterparts.6ꢀ8
materials by these methods. It is well known that for the
fabrication of solid devices for different applications, these Auꢀ
Pt NPs must be attached.17ꢀ21 Therefore, it is a great challenge
for the researchers to develop a simple and efficient method to
modify solid substrates with AuꢀPt NPs.
“Electroless deposition” is a term coined by Brenner and
Riddell to describe the spontaneous reduction of metal ions to
metallic particles in the absence of an external source of electric
current.22 It includes autocatalytic, substrate catalyzed and
galvanic displacement processes.23ꢀ28 In the substrate catalyzed
deposition, the substrate surface catalyzes the reduction of the
metal salt in the presence of a reducing agent. Once the film is
completely covered the substrate, reduction ceases because the
substrate is no longer exposed.26,27 Electroless deposition has
been demonstrated as a feasible method for the preparation of
bimetallic catalysts with more targeted placement of even small
amounts of the secondary metal.28 Bimetallic catalysts prepared
Among the different bimetallic NPs, AuꢀPt bimetallic NPs
received huge attention because they can be used for both fuel
cell and biosensors applications.9ꢀ12 Several methods have been
reported in the literature for the synthesis of AuꢀPt bimetallic
NPs which include radiolytic reduction, photolytic reduction
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

RSC Advances
Page 2 of 16
ARTICLE
VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C5RA06537B
by electroless deposition have been shown to have more
XPS measurements were carried out by using Shimadzu
intimate contact between the metals than catalysts prepared Axis 165 high performance multiꢀtechnique analysis using an
using traditional wet methods.29 Most importantly, the Al Kα source with pass energy of 80 eV, where the pressure in
secondary metal species in these new bimetallic compounds is the analysis chamber was lower than 1 × 10–8 Torr and the
preferentially deposited onto certain sites of the primary metal, dwell time was 458 ms. The binding energies for identical
leaving other active sites available for catalysis.29
samples were reproducible within ±0.10 eV. X–ray diffraction
Synthesis of bimetallic AuꢀPt NPs has been already reported analysis was carried out with a Rigaku X–ray diffraction unit
in the literature by several methods. Lou et al. prepared the using Ni–filtered Cu Kα (λ = 1.5406 A°) radiation. Scanning
carbon supported AuꢀPt bimetallic NPs by two phase synthesis electron microscope (SEM) measurements were carried at
with organic monolayer encapsulation on the nanocrystal core, VEGA3 TESCAN, USA. Energy dispersive Xꢀray analyses
followed by assembling on carbon black support material by were carried out using Bruker Nano, Germany. The
thermal calcinations. They showed that the lattice parameter of electrochemical measurements were carried out with CHI
bimetallic NPs scales varies linearly with respect to AuꢀPt electrochemical workstation (Model 643B, Austin, TX).
content in the composition.30 De and Rao reported the solꢀgel Electrochemical measurements were performed in
a
oriented synthesis of AuꢀPt alloys embedded in thin SiO2 films conventional twoꢀcompartment threeꢀelectrode cell with GCE
and showed the formation of coreꢀshell NPs of Au and Pt at as a working electrode, platinum wire as a counter electrode
elevated temperatures.31 Li et al. prepared the AuꢀPt core shell and NaClꢀsaturated Ag/AgCl as a reference electrode. All the
NPs by immobilizing Au colloids onto ethylenediamine electrochemical experiments were carried out under nitrogen
electrografted glassy carbon electrode (GCE) followed by atmosphere at room temperature.
underpotential deposition of copper by galvanic exchange
method.32 Schmid et al. reported the preparation of AuꢀPt
Electroless deposition of AuꢀPtNPs on GC electrode
bimetallic NPs with an Au core surrounded by Pt shell via
Prior to experiments, the GC electrode was polished with
2ꢀ
reducing PtCl6 by NH2OH in the presence of gold sol.33 The 0.5 ꢁm alumina and then ultrasonically cleaned in water for 5
AuꢀPt coreꢀshell NPs were also synthesized through chemical min. The electroless deposition of AuNPs on GC electrode was
deposition of PtNPs on selfꢀassembled AuNPs.34 Although Auꢀ carried out by immersing the well cleaned GCE into an aqueous
Pt bimetallic NPs were successfully prepared by different solution of each 0.3 mM HAuCl4 and NH2OH for 30 min.
methods, no report is available in the literature for the Then, the electrode was removed from the solution and rinsed
formation of both Au and PtNPs by electroless deposition with double distilled water. The AuNPs were deposited on the
method. Thus, the objective of the present study is to prepare GC electrode due to the reduction of Au3+ ions by NH2OH.
AuꢀPtNPs by electroless deposition and examine their This electrode is termed as GC/AuNPs electrode. The
electrocatalytic activity towards oxygen reduction reaction GC/AuNPs electrode was then immersed into a solution
(ORR) and hydrazine oxidation. The AuꢀPt NPs prepared by containing 0.01% each H2PtCl6 and NH2OH for 90 min to grow
electroless deposition were characterized by XPS, XRD, SEM, PtNPs. This electrode is termed as GC/AuꢀPtNPs electrode.
EDAX and CV. The SEM images showed that the deposited Scheme 1 illustrates the schematic representation for the
PtNPs on AuNPs show isotropic structure. The AuꢀPt NPs modification of GCE with AuꢀPt NPs. For XPS, XRD, SEM
modified electrode showed greater electrocatalytic activity and EDAX characterizations, ITO substrates with similar
towards ORR and hydrazine oxidation when compared to Au or modification were used.
Pt deposited GC electrodes.
Results and discussion
Experimental
Mechanism for electroless deposition of AuꢀPtNPs on GCE
Chemicals
The GC/AuNPs electrode was fabricated by electroless
hydrogen deposition method.26,27 The deposition bath contains HAuCl4
Platinic
acid
(H2PtCl6.6H2O)
and
tetrachloroaurate trihydrate (HAuCl4.3H2O) were purchased and NH2OH. Since NH2OH is thermodynamically capable of
from SigmaꢀAldrich and were used as received. Hydroxylamine reducing Au3+ ions, the deposition of AuNPs takes place on GC
hydrochloride (NH2OH. 2HCl), hydrazine dihydrochloride electrode. The initially deposited AuNPs catalyzes further
(NH2NH2.2HCl), sulfuric acid (H2SO4) and hydrogen peroxide growth of AuNPs and hence the size of AuNPs was increased.
(H2O2) were purchased from Merck, India and were used as The PtNPs were grown on GC/AuNPs electrode by immersing
received. 0.2 M phosphate buffer (PB) solution was prepared it into the solution containing H2PtCl6 and NH2OH. The AuNPs
using Na2HPO4 and NaH2PO4. All other chemicals were of on GCE act as the nucleation centre for the deposition of
analytical grade and were used as received. Double distilled PtNPs.33
water was used for preparing all solutions. Indium tin oxide
(ITO) plates were purchased from Asahi Beer Optical Ltd.,
Characterization of AuꢀPt NPs by UVꢀvis spectroscopy
Japan.
Figure S1 shows UVꢀvisible absorption spectra obtained for
AuNPs and AuꢀPtNPs modified ITO substrates. The AuNPs
modified substrate shows the characteristic SPR band at 581
Instrumentation
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 3 of 16
Journal Name
RSC Advances
View Article Online
ARTICLE
DOI: 10.1039/C5RA06537B
nm (Figure S1, curve a). When the PtNPs were grown on percentage of Pt and Au loading level is 19.5 and 17.28%,
AuNPs by immersing into a solution containing H2PtCl6 and respectively.
NH2OH for 30 min, the absorption intensity was decreased.
While increasing the immersion time to 45, 90 and 120 min, the
Characterization by SEM
SPR band was blue shifted and suppression of the Au plasmon
Further, the morphology and size of AuꢀPt NPs were
peak was noticed (Figure S1, curves bꢀd). This is in accordance characterized by SEM. Figure 2 shows the SEM images
with the report by LizꢀMarzan and Philipse.34 They suggested obtained for ITO/AuNPs and ITO/AuNPs immersed into a
that the Au plasmon absorption peak became suppressed with solution containing H2PtCl6 and NH2OH for 45, 90 and 120
the increase of surface coverage of Pt and finally vanished min. The SEM image of ITO/AuNPs shows that the deposited
when a complete Pt monolayer was formed.34 The obtained AuNPs were spherical in shape and the size of the AuNP was
spectral results confirmed that the PtNPs were deposited on the found to be 30 nm (Figure 2a). When the AuNPs modified
AuNPs modified substrate.
substrate was immersed into the H2PtCl6 and NH2OH solution,
the PtNPs were grown on the surface of the AuNPs and this
was monitored by SEM. For 45 min immersion, the size of the
Characterization of AuꢀPt NPs by XPS
Figure 1 shows XPS spectrum of AuNPs and bimetallic Auꢀ NPs was found to be increased to 50 nm compared to AuNPs
2ꢀ
Pt NPs. XPS of AuNPs deposited on ITO substrate for 30 min alone. This is due to the reduction of PtCl6 by NH2OH,
shows peaks at 83.6 and 87.3 eV with a difference of 3.7 eV catalyzed by the AuNPs seeds which are deposited on the ITO
corresponds to the 4f7/2 and 4f5/2 of Au, respectively which is substrate. The AuNPs seeds act as the nucleation centre. Hence,
consistent with the zero valent nature of Au (Figure 1 A).35,36 the growth of PtNPs was facilitated by the Au seeds deposited
On the other hand, deposition of PtNPs on ITO/AuNPs for 45 on the ITO surface (Figure 2b). When the immersion time was
min shows four peaks at 71.2, 74.4, 83.6 and 87.3 eV. The increased to 90 min, the size of the PtNPs was further increased
obtained 71.2 and 74.4 eV are the characteristic peaks of 4f7/2 and the growth of PtNPs was promoted by the initially
and 4f5/2 of zero valent nature of Pt, respectively (Figure 1 B).37 deposited PtNPs on the AuNPs modified substrate. Here, the
In contrast to Figure 1 A, the intensity of the Au peaks were initially deposited PtNPs act as the nucleation centre and the
decreased after the deposition of PtNPs. It has been already growth of PtNPs was found to be high (Figure 2c). For 120
reported that when the Pt layer is not thick enough the XPS min, the growth process was attained the saturation due to large
instrument can detect the signal of Au whereas it cannot detect size of initially deposited PtNPs (Figure 2d). These results
XPS signal when thick layer of Pt covered the AuNPs.33 Based suggested that the growth of PtNPs on the surface of the AuNPs
on this result, it is proposed that the AuꢀPt bimetallic takes place at the optimum time of 90 min and the formed
nanoparticles should have a coreꢀshell structure.33 Similarly, in nanostructures are in the form of Au(core)ꢀPt(shell). Similar
the present study, the intensity of the Au signal (Figure 1A) was deposition of AuꢀPt NPs was also carried out on GC substrate.
dramatically decreased after the deposition of PtNPs on ITO/Au Figure S4 shows the SEM images obtained for (a) GCE/AuNPs
(Figure 1B). From the decrease in intensity of Au signal, it is and (b) GCE/Au@PtNPs for the optimum deposition time of 30
assumed that the present method of electroless deposition of Pt min for Au and 90 min for Pt. The AuNPs modified GCE
NPs on AuNPs leads to the formation of coreꢀshell structure, in shows that the NPs were spherical with the average size of 30
which Au core being coated by a shell of Pt metal.
nm (Figure S4a). When the GCE/AuNPs was modified with
PtNPs the size of the NPs was found to be increased to 90 nm
(Figure S4b).
Characterization of AuꢀPt NPs by XRD and EDAX
Figure S2 shows the XRD pattern of the AuꢀPt NPs. It
illustrates the diffraction features appearing at 34.97°, 38.16°,
44.35°, 50.34°, 55.73°, 60.01°, 74.08° and 77.28°. The peaks at
Electrochemical characterization of GC/AuꢀPtNPs electrode
Figure S5 shows the CVs obtained for AuNPs deposited GC
34.97°, 44.35°, 55.73° and 74.08° corresponding to Au (111), electrode with different electroless deposition time. The
Au (200), Au (220) and Au (311) planes, respectively (JCPDS oxidation and reduction peaks were observed at +0.90 V and
card No. 04ꢀ0802). The peaks at 38.16°, 50.34°, 60.01° and +0.40 V, corresponding to the oxidation and subsequent
77.28° corresponding to Pt (111), Pt (200), Pt (220) and Pt reduction of gold oxide, respectively. The surface coverage was
(311) planes, respectively (JCPDS card No. 03ꢀ065ꢀ2870). The calculated using the following equation.29,36
peak corresponding to the Pt (111) plane is more intense than
Au oxide reduction charge (ꢁC)/723 (ꢁC/cm2)
the other planes, suggesting that it is a predominant orientation.
Besides, compared with Au (111), the peak intensity of Pt (111)
is much higher, implying that Au (core)ꢀPt (shell) orientation.
(1)
× 100
θp =
Geometric area of the electrode (cm2)
Further, the AuꢀPt NPs modified substrate was characterized by where, 723 ꢁC/cm2 corresponds to the charge of an
EDAX analysis. Figure S3 shows EDAX spectrum obtained for electrochemically grown monolayer of gold oxide.36,37 The
AuꢀPt NPs modified ITO substrate. The peaks at 2.12 and 9.71 particle coverage was found to be 2.7, 7,1 and 9.2%
keV are the characteristic peaks for Au and 2.05 and 9.44 keV corresponding to the immersion time of 10, 20 and 30 min,
are the characteristic peaks for Pt, confirming the presence of respectively.
both Au and PtNPs on the ITO substrate and the weight
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

RSC Advances
Page 4 of 16
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5RA06537B
Figure 3 shows CVs obtained for bare GCE, GCE/AuNPs reduction occurs at −0.45 V (Figure 4, curve a). When AuNPs
and GC/Au@Pt NPs electrode prepared with electroless were deposited on the GCE, the dioxygen reduction
deposition time of 120 min in 0.5 M H2SO4 at a scan rate of 10 overpotential was reduced by 50 mV (ꢀ0.40 V) (Figure 4, curve
mVsꢀ1. Bare GCE does not show any obvious oxidation and b). The onset potential for ORR at the GC/AuꢀPtNPs electrode
reduction peak response in 0.5 M H2SO4 (Figure 3A, curve a). (0.20 V) (Figure 4, curve c) is significantly more positive than
When the electrode was modified with AuNPs, it shows Au the bare GCE (ꢀ0.45 V) and GC/AuNPs (ꢀ0.40 V) electrodes.
oxidation peak at +1.25 V and Au oxide reduction peak at The GC/Au@PtNPs electrode not only shifted the dioxygen
+0.90 V (Figure 3A, curve b). On the other hand, when the reduction potential to more positive potential but also markedly
PtNPs were deposited on AuNPs, exhibit the characteristic increased its reduction current when compared to bare and
hydrogen adsorptionꢀdesorption peaks at ꢀ0.25 V and the Pt AuNPs modified GCE. The obtained large shift in the onset as
oxide reduction peak at 0.60 V (Figure 3A, curve c). For well as the reduction peak potential at the GC/Au@PtNPs
different times of immersion, the hydrogen adsorption and electrode indicate that the Au@PtNPs efficiently catalyzed the
desorption peaks were increased and after 90 min time of reduction of dioxygen. The electrocatalytic activity of the
deposition, were decreased. The deposition of PtNPs was facile GC/Au@PtNPs electrode towards dioxygen reduction was
on AuNPs deposited at 30 min compared to high or less further examined by varying the deposition time (30, 45, 90 and
deposition time of AuNPs. For less than 30 min deposition 120 min) of PtNPs. The electroless deposition of PtNPs on
time, the rate of growth of PtNPs on AuNPs modified substrate GC/AuNPs electrode at the deposition time of 90 min shows
is very less whereas for more than 30 min the size of AuNP was higher catalytic activity towards dioxygen reduction (Figure S6,
found to be high and thus it does not catalyze the reduction curve c) compared to other deposition times. This is due to the
effectively. Hence, the optimization time of 30 min was fixed complete coverage and size effect of the PtNPs. The catalytic
for the deposition of AuNPs. For the GC/AuꢀPt electrode, the activity towards dioxygen reduction decreases when the
Au oxide reduction peak at +0.9 V still can be observed but it deposition time was increased to more than 90 min (curve d).
becomes suppressed with an increasing amount of Pt (Figure This is due to the overgrowth of PtNPs on GC/AuNPs
3A and B). When the Pt:Au ratio is raised by increasing the electrode.
immersion time, the Au oxide reduction peak was completely
The ORR was also carried out at Au@Pt modified electrode
disappeared. This reveals that Pt is deposited on the Au surface by rotating disc electrode (RDE). Figure 5A shows the
instead of forming its own nucleus. Moreover, the presence of hydrodynamic voltammograms for the ORR at GC/Au@PtNPs
the Pt oxide reduction peak at +0.60 V along with the less electrode in O2 saturated 0.5 M H2SO4 at electrode rotation
intense Au oxide reduction peak at +0.90 V suggests that few rates in the range of 400 to 1600 rpm and at a potential scan
exposed Au sites still remain on the surface. Based on the Au rate of 50 mV sꢀ1. A gradual increase in the limiting current
oxide reduction peak areas before and after the deposition of Pt was observed while increasing the rotation owing to the
shell, it is estimated that 10% of the originally existed Au is increase in the mass transport to the electrode surface (Figure
electrochemically active after the deposition of the Pt shell.31
5A). The observed current density is normalized to the
geometric area of the electrode in the respective curves.
According to the Koutecky–Levich equation (Equation 5), the
Electrocatalytic reduction of dioxygen
The oxygen reduction reaction (ORR) is one of the most inverse of current density could be given as the sum of the
important reactions in life processes including biological inverses of the above current components. It could also be
respiration and in energy converting systems such as fuel cells.
given in terms of jk,
(rpm).
B
and ω expressed in revolution per minute
O2 + 4H+ + 4eꢀ → 2H2O
O2 + 2H+ + 2eꢀ → H2O2
H2O2 + 2H+ + 2eꢀ → 2H2O
(2)
(3)
(4)
1/j
= 1/ k
j
+ 1/
B
ω1/2
(5)
where, j is the current density, jk is the kinetic current density.
is evaluated by Equation (5a).
= 0.2nFCO2(DO2
2/3νꢀ1/6
B
The generalized mechanism for the ORR in acid medium is
shown in equations 2ꢀ4.38,39 Bulk oxygen approaches the
surface by diffusive mass transport where two parallel reaction
pathways occur and the dominant reaction pathway is
determined by the type of molecular chemisorptions.
Depending on the interaction of O2 with the catalyst surface,
the oxygen reduction will either proceed via the direct fourꢀ
electron reduction of oxygen to water (Equation 2) or twoꢀ
electron reduction of oxygen as peroxide route (Equations 3
and 4).38,39 The electrocatalytic activity of the Au@PtNPs ORR
was examined by cyclic voltammetry. Figure 4 shows the CVs
obtained for bare GCE, GCE/AuNPs and GCE/Au@PtNPs in
an oxygen saturated 0.5 M H2SO4. At bare GCE, dioxygen
B
)
(5a)
where, 0.2 is a constant. n is the number of electrons
transferred per mole of oxygen, F is Faraday constant (96 485 C
molꢀ1), CO2 is the bulk concentration of the oxygen (1.1×10ꢀ6
mol cmꢀ3), DO2 is the diffusion coefficient of oxygen in sulfuric
acid (1.4×10ꢀ5 cm2 sꢀ1) and ν is kinematic viscosity of sulfuric
acid (1.0×10ꢀ2 cmꢀ2 sꢀ1).40,41 The Au@Pt NPs modified electrode
(Figure 5B) shows the linear relationship of jꢀ1 vs. ωꢀ1/2. The
slope (
calculate the number of electrons involved in ORR. The Au@Pt
NPs modified electrode shows
value of 14.48×10ꢀ2 mA cmꢀ2
B) of the straight line of K–L plot could be used to
B
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 5 of 16
Journal Name
RSC Advances
View Article Online
ARTICLE
DOI: 10.1039/C5RA06537B
rpmꢀ1/2 and its corresponding n value is 2.46. The theoretical
B
of ꢀ0.175 to 0.35V, the electrode fabrication is time consuming
value calculated for 2ꢀelectron transfer process is 17.2×10ꢀ2 mA (13ꢀ15 h).
cmꢀ2 rpmꢀ1/2 40
The experimental and n values are close to the
.
B
Conclusions
theoretical values. This observation confirms that the Au@Pt
NPs modified GCE follows two electron pathway for reduction
of oxygen as shown in Equation 3.
The assemblies of Au@Pt coreꢀshell NPs were prepared by
electroless deposition method on GC electrode using the
concept of substrate catalyzed electroless deposition. XPS
results confirmed the zero valent nature of both Au and Pt.
SEM images revealed that the deposited AuNPs on GCE and
PtNPs on AuNPs/GCE were uniform and isotropic. The
GC/Au@PtNPs modified electrode was effectively catalyzed
the dioxygen reduction by not only shifting its reduction
potential towards less positive potential but also enhanced its
reduction current when compared to bare GC electrode. The
oxidation of hydrazine was also studied using the present
modified electrode. It was found that Au@PtNPs modified
electrode effectively catalyzed the oxidation of hydrazine by
shifting the oxidation potential to less negative potential with
enhanced current.
Electrocatalytic oxidation of hydrazine
Hydrazine is a highly reactive base and is used as an ideal
fuel for direct hydrazine fuel cell. It is a promising one due to
its more hydrogen content, higher electromotive force and
absence of exhaust of greenhouse gases during oxidation when
compared to other fuel cells.42 Thus, the electrochemical
oxidation of hydrazine received great interest in the field of fuel
cells. The proposed mechanism for electrochemical oxidation
of hydrazine in acidic and basic solution at platinum electrode
is given in Scheme 2.43 Figure 6 shows the CVs obtained for
bare GCE, AuNPs and Au@PtNPs modified GCEs in the
presence of 0.5 mM hydrazine in 0.2 M PBS (pH 7.2) at a scan
rate of 50 mV sꢀ1. The bare GCE and AuNPs modified GCE
show broad oxidation peaks for hydrazine at +0.73 V and +0.48
V, respectively (Figure 6; curves a and b). Interestingly, the
oxidation peak for hydrazine was shifted towards less negative
potential (ꢀ0.26 V) with enhanced current at GC/Au@PtNPs
modified electrode (Figure 6; curve c). This infers that the
Au@PtNPs modified electrode effectively enhanced the
catalytic activity towards hydrazine oxidation when compared
to bare and AuNPs modified GCEs. It has been already
reported that the hydrazine oxidation depends on the pH of the
electrolyte solution.44 Therefore, oxidation of hydrazine at
different pH was studied using CV. Figure S7 shows the
oxidation of 0.5 mM hydrazine at AuꢀPtNPs modified GCE in
different pH at a scan rate of 50 mV sꢀ1. The oxidation potential
was shifted towards less positive potential upon increasing the
pH from 3 to 8 (curves aꢀf). The plot of potential vs. pH gives a
slope value of 90 mV/pH. This value is close to the Nernstian
slope of 59 mV/pH at 25° C, indicating the number of proton
and electron in the electrode process is equal. Figure S8 shows
the CVs obtained for 0.5 mM hydrazine at Au@PtNPs
modified GCE in PBS (pH 7.2) at different scan rates. The
oxidation current of hydrazine was increased while increasing
the scan rate. A good linearity between the anodic current of
hydrazine and square root of scan rate was obtained with a
correlation coefficient of 0.993 (Figure S8, inset) at scan rates
from 25 to 250 mV sꢀ1. This indicates that the oxidation of
hydrazine is a diffusion controlled process at GCE/Au@PtNPs.
The Au@Pt modified electrode prepared by the present
method showed excellent performance towards hydrazine
oxidation compared to the existing Pt and other nanoparticle
modified electrodes (Table 1).45ꢀ51 The electrode which shows
the oxidation of hydrazine at less positive potential is preferred
for the analysis of hydrazine. The oxidation potential of
hydrazine obtained at the present modified electrode is
remarkably less positive potential with respect to the reported
modified electrodes.45ꢀ51 Although Pd and Au nanoparticle
modified electrode could detect hydrazine in the potential range
Acknowledgement
N.S.K. Gowthaman thanks the University Grants Commission
(UGC), New Delhi, India for the award of a Meritorious
Student Fellowship (F. 7ꢀ225/2009(BSR)). Financial support
from
Department
of
Biotechnology
(BT/PR10372/PFN/20/904/2013), New Delhi, India is
gratefully acknowledged.
Address
Centre for Nanoscience and Nanotechnology, Department of
Chemistry, Gandhigram Rural Institute, Gandhigramꢀ624302,
Dindigul, Tamilnadu, India; E–mail: abrajohn@yahoo.co.in,
s.abrahamjohn@ruraluniv.ac.in; Tel: +91 451 245 2371; Fax :
+ 91 451 245 3031.
Electronic Supplementary Information (ESI) Available:
UVꢀvis absorption spectra, XꢀRay diffraction pattern and
EDAX spectrum obtained for ITO/AuꢀPtNPs, SEM images and
CVs obtained for GC/AuNPs at different deposition times,
dioxygen reduction at GC/Au@PtNPs at different deposition
times and effect of pH and scan rates on hydrazine oxidation
for Au@PtNPs modified electrode is available in the online
version of this article. See DOI: 10.1039/b0000.
References
1. J.H. Sinfelt, Acc. Chem. Res., 1977, 10, 15.
2. J.H. Sinfelt, Bimetallic Catalysts: Discoveries, Concepts and
Applications; John Wiley and Sons: New York, 1983
.
3. J.H. Sinfelt, G.W. Dembinski, U.S. patent, US3442973, 1969.
4. C.T. Campbell, Annu. Rev. Phys. Chem., 1990, 41, 775.
5. J.A. Rodriguez, Surf. Sci. Rep., 1996, 24, 225.
6. J.G. Chen, C.A. Menning, M.B. Zellner, Surf. Sci. Rep., 2008, 63
201.
,
7. J.R. Kitchin, J.K. Norskov, M.A. Barteau, J.G. Chen, Phys. Rev.
Lett., 2004, 93.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

RSC Advances
Page 6 of 16
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5RA06537B
8. B.N. Wanjala, J. Luo, B. Loukrakpam, B. Fang, D. Mott, P. Njoki, 45. G. Hu, Z. Zhou, Y. Guo, H. Hou, S. Sho, Electrochem. Commn.,
M. Engelhard, J.K. Wu, O. Malis, C.J. Zhong, Chem.Mater., 2010,
22, 4282.
2010, 12, 422.
46. Y. Liu, B. Li, W. Wei, Q. Wan, N. Yang, Adv. Mater. Res., 2013,
9. J. Luo, M.M. Maye, N.N. Kariuki, L.Y. Wang, P. Njoki, Y. Lin, M.
Schadt, H.R. Naslund, C.J. Zhong, Catal. Today, 2005, 99, 91.
10. X.H. Kang, Z.B. Mai, X.Y. Zou, P.X. Cai, J.Y. Mo, Ana. Biochem.,
2007, 369, 71.
704, 246.
47. R. Madhu, V. Veeramani, SꢀM. Chen, Sensors and Actuators B,
2014, 204, 382.
48. W. Zhou, L. Xu, M. Wu, L. Xu, E. Wang, Anal. Chim. Acta, 1994,
299, 189.
11. N. Kristian, Y. Yan, X. Wang, Chem, Commun., 2008, 353.
12. G.C.Bond, Platinum Met. Rev., 2007, 51, 63.
49. A.P. O’Mullane, S.E. Dale, J.V. Macpherson, P.R. Unwin,
Chem.Commun., 2004, 1606.
13. M. Harada, K. Asakura, N. Toshima, J. Phys. Chem., 1993, 97, 5103.
14. H.Y. Heng, P.C. Gibbons, K.F. Kelton, W.E. Buhro, J. Am. Chem. 50. S. Chakraborty, C.R. Raj, Sensors and Actuators B, 2010, 147, 222.
Soc., 1997, 119, 10382.
51. L.T. Tamsiunaite, J. Rakauskar, A. Balciunaite, A. Zabielaite, J.
Vaiciuniene, A. Selskis, R. Juskenas, V. Pahstar, E. Norkus, J. Power
Sources, 2014, 272, 362.
15. F. Baletto, C. Mottet, R. Ferrando, Phys. Rev. Lett., 2003, 90
,
135504.
16. R. Crooks, M. Zhao, Adv. Mat., 1999, 11, 217.
17. R. Dey, C.R. Raj, Chemistry-An Asian Journal, 2012,
18. B.K. Jena, C.R. Raj, Langmuir, 2007, 23, 4064.
19. B.K. Jena, C.R. Raj, Chem. Mater., 2008, 20, 3546.
7, 417.
20. H. Ye, R.M. Crooks, J. Am. Chem. Soc., 2005, 127, 4930.
21. A. Brenner, E. Riddell, J. Res. Natl. Bur. Std., 1946, 37, 3.
22. Y. Okinaka, T. Osaka, Adv. Electrochem. Sci. Eng., 1994,
23. Y. Okinaka, M. Hoshino, Gold Bull., 1998, 31, 3.
3, 55.
24. G.O. Mallory, J.B. Hajdu, Eds.; AESF: Orlando, FL, 1990.
25. M. Kato, J. Sato, H. Otani, T. Homma, Y. Okinaka, O. Yoshioka, J.
Electrochem. Soc., 2002, 149, 164.
26. J. Sato, M. Kato, H. Otani, T. Homma, Y. Okinaka, O. Yoshioka, J.
Electrochem. Soc., 2002, 149, 168.
27. G. Oskam, J.G. Long, A. Natarajan, P.C. Searson, J. Phys. D, 1998,
31, 1927.
28. S. Kumar, S. Zou, J. Phys. Chem. B, 2005, 109, 15707.
29. Y. Lou, M.M. Maye, L. Han, J. Luo, C.ꢀJ. Zhong, Chem. Commun.,
2001, 473.
30. G. De, C.N.R. Rao, J. Mater. Chem., 2005, 15, 891
31. Y. Li, Q. Lu, S. Wu, L. Wang, X. Shi, Biosensors and Bioelectronics,
2013, 41, 576.
32. G. Schmid, A. Lehnert, J. Malm, J. Bovin, J. Angew. Chem., Int. Ed.
Engl., 1991, 7, 30.
33. L. Cao, L. Tong, P. Diao, T. Zhu, Z. Liu, Chem. Mater., 2004, 16
,
3239.
34. L.M. LizꢀMarzan, A.P. Philipse, J. Phys. Chem., 1995, 99, 15120.
35. P. Kannan, S.A. John, Electrochim. Acta, 2010, 55, 3497.
36. N. Alexeyeva, K. Tammeveski, Anal. Chim. Acta, 2008, 618, 140.
37. T. Matsumoto, T. Komatsu, K. Arai, T. Yamazaki, M. Kijima, H.
Shimizu, Y. Takasawab, J. Nakamura, J. Chem. Commun., 2004, 840.
38. R.A. Sidik, A.B. Anderson, J. Electroanal. Chem., 2002, 528, 69.
39. R.S. Arnald, J. Shi, E. Murad, A.M. Whalen, C.Q. Sun, R.
Polavarapu, S. Parthasarathy, J.D. Lambeth, Proc. Natl. Acad. Sci.
U.S.A., 2001, 98, 5550.
40. J.J. SalvadorꢀPascual, S. CitalanꢀCigarroa and O. Solorzaꢀ Feria, J.
Power Sources, 2007, 172, 229.
41. J. Zeng, S. Liao, J.Y. Lee and Z. Liang, Int. J. Hydrogen Energy
2010, 35, 942.
,
42. A. Serov, C. Kwak, Appl. Catal., B 2010, 98, 1.
43. S. Hwang, J. Lee, J. Kwak, J. Electroanal. Chem., 2005, 579, 143.
44. S.V. Guerra, C.R. Xavier, S. Nakagaki, L.T. Kubota, Electroanalysis,
1998, 10, 462.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 7 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
Figures
Au 4f7/2
Pt 4f7/2
Pt 4f5/2
A
B
Au 4f5/2
400
200
0
400
Au 4f7/2
Au 4f5/2
200
90
80
100
80
60
Binding energy (eV)
Binding energy (eV)
Figure 1. XPS obtained for (A) ITO/AuNPs and (B) ITO/Au@Pt NPs.

RSC Advances
Page 8 of 16
View Article Online
DOI: 10.1039/C5RA06537B
a
c
b
d
Figure 2. SEM images obtained for (a) ITO/AuNPs and ITO/AuNPs immersed into the
solution containing H2PtCl6 and NH2OH for (b) 45, (c) 90 and (d) 120 min.

Page 9 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
10
0
200
200
d
a
–10
–20
Pt
Au
c
0.5
1
E/V vs. Ag/AgCl (NaCl sat)
0
0
a
b
–200
–200
A
B
0
1
0
1
E/V vs. Ag/AgCl (NaCl sat)
E/V vs. Ag/AgCl (NaCl sat)
Figure 3. (A) CVs obtained for (a) bare GCE, (b) GCE/AuNPs and (c) GC/Au@Pt NPs
electrode prepared with electroless deposition time of 120 min in 0.5 M H2SO4 at a scan rate
of 10 mVs-1. Inset: Gold oxide and platinum oxide reduction peaks. (B) CVs obtained for
GC/Au@Pt NPs electrode prepared with electroless deposition time of 30, 45, 90 and 120
min in 0.5 M H2SO4 at a scan rate of 10 mVs-1.

RSC Advances
Page 10 of 16
View Article Online
DOI: 10.1039/C5RA06537B
0
–20
–40
–60
a
b
c
–0.5
0
0.5
E/V vs. Ag/AgCl (NaCl sat)
Figure 4. CVs obtained for dioxygen reduction at (a) bare GCE, (b) GCE/AuNPs and (c)
GCE/Au@Pt NPs electrode in O2 saturated 0.5M H2SO4 at a scan rate of 50 mV s-1.

Page 11 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
0
–200
–400
0.75
0.70
0.65
0.60
0.55
0.50
0.45
A
B
y=14.48x + 0.021
R2=0.998
400 rpm
625 rpm
900 rpm
1225 rpm
1600 rpm
0.40
0.35
0.025
0.030
0.035
0.040
0.045
0.050
–0.2
0
0.2
0.4
0.6
ω-1/2 / rpm-1/2
E/V vs. Ag/AgCl (NaCl sat)
Figure 5. (A) Steady-state voltammograms for the ORR obtained at GC/Au@PtNPs
electrode in O2 saturated 0.5 M H2SO4. Rotation rate: 400, 625, 900, 1225 and 1600 rpm.
Scan rate: 50 mV s-1. (B) Corresponding K-L plot.

RSC Advances
Page 12 of 16
View Article Online
DOI: 10.1039/C5RA06537B
30
20
10
0
c
a
b
0
1
E/V vs. Ag/AgCl (NaCl sat)
Figure 6. CVs obtained for 0.5mM hydrazine at (a) bare GCE, (b) GCE/AuNPs and (c)
GCE/Au@Pt NPs in 0.2 M PBS (pH 7.2) at a scan rate of 50 mV s-1.

Page 13 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
Au3+
Au0
Oxd
Red
0.3 mM
HAuCl + NH OH
0.3 mM
H PtCl + NH OH
4
2
2
6
2
ne-
GCE
GCE
Sub0
Substrate
Au
Pt
Scheme 1. Schematic representation for the mechanism of electroless deposition of Au@Pt
NPs on GCE.

RSC Advances
Page 14 of 16
View Article Online
DOI: 10.1039/C5RA06537B
Acidic Medium
N2H5+(soln)
Basic Medium
N2H5+(ads)
N2H4+ + H+ + e-
N2H4(soln)
N2H4(ads) + OH-
N2H4(ads)
slow
slow
+
N2H3 + H2O + e-
N2 + 3H2O + 3e-
N2H5 (ads)
fast
fast
N2H3 + 3OH-
N2H4+
N2 + H+ + 3e-
Scheme 2. Mechanism for electrochemical oxidation of hydrazine in acidic and basic
solutions at platinum electrode.

Page 15 of 16
RSC Advances
View Article Online
DOI: 10.1039/C5RA06537B
Table 1
Comparison of oxidation potential of hydrazine oxidation over various modified
electrodes.
Oxidation
S.No
Electrodes
pH
Referenec
Potential (vs.
Ag/AgCl), V
0.38
1
2
3
4
5
6
7
8
nRh/CNF
Au/PdNPs/Graphene
AC/Au
neutral
neutral
neutral
neutral
neutral
neutral
alkaline
neutral
[42]
[43]
0.2
0.13
1
[44]
PtNPs/CNF
[45]
PAni/PtNPs
0.439
-0.35
0.2
[46]
PtNPs/MWCNT
Au/TiO2NTs
Au@Pt Nps
[47]
[48]
-0.25
This work
nRh/CNF- rhodium nanoparticles loaded carbon nanofibres, Au/PdNPs/Graphene – Gold palladium bimetallic
nanoparticles loaded graphene, Ac/Au – gold nanospheres – activated carbon nanocomposites, PtNPs/CNF –
platinum nanoparticles coated CNF, PAni/PtNPs – polyaniline – PtNPs nanocomposites, PtNPs/MWCNT –
PtNPs loaded multiwalled carbon nanotubes, Au/TiO2NTs – gold-titanium dioxide nanotubes

RSC Advances
Page 16 of 16
View Article Online
DOI: 10.1039/C5RA06537B
Graphical abstract
Gold@platinm core-shell nanoparticles were modified on glassy carbon electrode by
electroless deposition method and then used for the electrocatalytic reduction of dioxygen
and oxidation of hydrazine.