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Electrochimica Acta 100 (2013) 164– 170

Contents lists available at SciVerse ScienceDirect

Electrochimica Acta

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ulsed electrodeposition of Pt particles on indium tin oxide substratesnd their electrocatalytic properties for methanol oxidation

ie Liua, Cheng Zhonga,∗, Xintong Dua, Yating Wua, Peizhi Xua, Jinbo Liub,c, Wenbin Hua,∗

State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, ChinaDepartment of Chemistry, Texas A&M University-Kingsville, MSC 161, Kingsville, TX 78363-8012, United StatesAdvanced Light Source, ALS Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States

a r t i c l e i n f o

rticle history:eceived 31 January 2013eceived in revised form 28 March 2013ccepted 28 March 2013vailable online 6 April 2013

eywords:t catalystsulsed electrodepositionurface morphologyethanol oxidation

a b s t r a c t

The platinum (Pt) particle electrocatalysts supported on the indium tin oxide (ITO) substrate were pre-pared by the pulsed electrodeposition for the methanol oxidation. The effect of the lower potential pulseduration (tl) of the electrodeposition on the surface morphology and structure of the Pt particles wasinvestigated by the X-ray diffraction and scanning electron microscopy. The amount of the Pt loadingwas determined by an inductively coupled plasma method, and the electrocatalytic activity of the pre-pared Pt electrocatalysts on the ITO for the methanol oxidation was characterized by cyclic voltammetry.The results showed that the tl has a significant influence on the surface morphology of the Pt particles onthe ITO substrate. As the tl decreases from 1 to 0.01 s, the deposited Pt particles on the ITO exhibit flower-,nanosheet-, prickly and smooth spherical-like morphology in turn. Furthermore, there is a remarkableeffect of the surface morphology of the Pt particles on the electrocatalytic activity for the methanol oxi-

ndium tin oxide dation. Among all these morphologies, the flower- and nanosheet-like Pt particles on the ITO have amuch higher mass specific activity (MA) for the methanol oxidation, and the Pt particles with pricklysurface followed while the smooth spherical Pt particles have the lowest MA. In particular, the dispersedPt nanosheets prepared at tl of 0.5 s has the highest MA. The much improved MA of the dispersed Ptnanosheets is attributed not only to the large electrochemically active surface area (ECSA) achieved, butalso to the high electrocatalytic activity per unit ECSA related to its special morphology.

. Introduction

Noble metal micro- and nanoparticles have attracted consider-ble and increasing attention in a variety of important applicationsuch as catalysis, biological labeling, optics and electronics [1,2]. Forarticular applications such as electrocatalysis and electrochemi-al sensors, it is essential to support the noble metal particles on anppropriate conductive substrate [3–5]. Typical support materialsnclude carbon-based materials (e.g., carbon black, glassy carbon,arbon fiber and carbon nanotubes) [6–8], metallic materials (e.g.,u, Ni and Ti) [9,10] and metal oxides (e.g., TiO2) [11]. Recently, thepplication of indium tin oxide (ITO) as the support has receivedncreasing interest due to its low cost and prominent charac-eristics including high electrical conductivity, excellent opticalransparency, wide electrochemical working window, and stable

lectrochemical and physical properties [3–5,12–15]. For example,yama et al. [16–18] prepared Au, Ag particles on the ITO sur-

ace using seed-mediated growth method and Pt particles on the

∗ Corresponding authors. Tel.: +86 21 34202981; fax: +86 21 34202981.E-mail addresses: chengz@sjtu.edu.cn (C. Zhong), material hu@163.com (W. Hu).

013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.electacta.2013.03.152

© 2013 Elsevier Ltd. All rights reserved.

ITO by chemical reductive growth method. The fabricated Au, Agand Pt/ITO electrodes exhibit high electrocatalytic activity for theelectro-oxidation of nitric oxide [16], the reduction of the methylviologen [17] and the oxygen reduction and methanol oxidationrespectively [18]. It was found that the oxidation peak current of thePt nanoparticles on the ITO increased over three times comparedwith the bulk Pt electrode for methanol oxidation [18]. Ballarinet al. [13,19] prepared Au–Pt and Au nanoparticles on the ITOelectrodes by electrosynthesis and sputtering respectively, whichshowed promising results for methanol oxidation. In the authors’previous work, it has also been demonstrated that the Pt/ITO elec-trodes can be successfully used for ammonia oxidation [20,21].

Up to date, a number of preparation methods, such as theseed mediated growth [16,17,22–25], sputtering [13,26], chem-ical reduction [18,27] and electrodeposition [12,19,20,28–31],have been developed to prepare the noble metal particles onthe ITO. Among these methods, electrodeposition technique isof particular interest due to its unique advantages including

high purity of deposits, low cost of implementation and easy-to-control procedure [32–34]. Various electrodeposition methods,including galvanostatic electrodeposition [21,28,29], potentio-static electrodeposition [30,31] and electrodeposition in a cyclic

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oltammetric mode [20,35,36], have been successfully utilizedo prepare Pt, Au and Au–Pt particles on the ITO. Furthermore,ince the deposits are strongly dependent on the electrodeposit-ng conditions, it is expected that there are essential effects of thelectrodeposition methods and parameters on the electrocatalyticctivity of the prepared noble metal particles on the ITO [7,19,29].revious studies concerning the pulsed electrodeposition on otherubstrates found that the pulsed electrodeposition favors the for-ation of nucleation sites and thus contributes to a high dispersion

f the deposits compared with other electrodeposition methods37–40], which has a potential advantage on improving the catalyticctivity of the prepared electrocatalysts. However, there has beeno report focusing on the pulsed electrodeposition of noble metallectrocatalysts on the ITO substrates. Furthermore, the paramet-ic influence of the pulsed electrodeposition (e.g., lower potentialulse duration tl) on the formed noble metal particles on the ITOnd the corresponding electrocatalytic activities have remainednclear.

In the present work, the pulsed electrodeposition was used torepare the Pt particles on the ITO substrate for the methanolxidation. The effect of the tl of the pulsed electrodeposition onhe surface morphology and structure of the deposited Pt parti-les were characterized by scanning electron microscopy (SEM)nd X-ray diffraction (XRD). The exact amount of the deposited Ptas determined by an inductively coupled plasma (ICP) method.

urthermore, the relationship between the surface morphology ofhe Pt deposits and the electrocatalytic activity for the methanolxidation were investigated by cyclic voltammetry (CV).

. Experimental

.1. Preparation of Pt/ITO electrode

The ITO glasses (Southern Glass Co., Ltd., Shenzhen, China) weresed after being washed in acetone and ultrapure water by sonica-ion and drying with a nitrogen steam. Pt particles were preparedn an ITO substrate by the pulsed electrodeposition in 5 mmol L−1

2PtCl6 and 0.5 mol L−1 H2SO4 solution. The electrodeposition waserformed in a classical three electrode cell, using a sheet of ITOith an exposed geometry area of 1 cm2 as the working electrode,

mercury sulfate electrode (MSE) as the reference electrode, and Pt plate as the counter electrode. All solutions were preparedith ultrapure water obtained from a water purification system

Millipore, 18.2 M� cm). Fig. 1 shows the schematic diagram ofhe pulsed electrodeposition. The upper potential limit (Eu), lowerotential limit (El) and the upper potential pulse duration tu were.1 V (MSE), −1 V (MSE) and 1 s, respectively. The lower potential

ulse duration tl was changed between 0.01 and 1 s. The total timef tl under different electrodeposition conditions are all set as 20 s.hen only Eu is applied, i.e., tl = 0 s, there are no Pt particles formed

Fig. 1. Schematic diagram of the potentiostatic pulsed electrodeposition.

a 100 (2013) 164– 170 165

on the substrate. While only El is applied, i.e., tu = 0 s, the formed Ptparticles are quite similar to those formed at tl = 1 s and tu = 1 s.

2.2. Characterizations of surface morphology, structure andamount of the deposited Pt on ITO

The surface morphology of the deposited Pt particles on the ITOsubstrate was obtained using a field-emission SEM (FEI Sirion 250).The crystalline structure of the Pt particles was characterized byan XRD (BRUKER-AXS) using Cu K� radiation (� = 0.15406 nm) ata scan rate of 0.5◦ min−1. The exact amount of the Pt deposits, i.e.,Pt loading, on an ITO substrate was determined by an ICP (ThermoScientific, iCAP 6000) method after dissolving Pt from the substrate.The Pt loading (�g cm−2) is normalized by the geometric area of theworking electrode.

2.3. Electrochemical characterizations

The electrocatalytic activity of the prepared Pt/ITO electrode forthe methanol oxidation was characterized by CV measurements inthe solution containing 0.5 mol L−1 H2SO4 and 1 mol L−1 CH3OH ata scan rate of 0.05 V s−1. The electrochemically active surface area(ECSA, cm2 cm−2) of the Pt deposited on the ITO was evaluated fromthe steady-state CVs recorded at 0.05 V s−1 in 0.5 mol L−1 H2SO4solution, and its value was normalized by the geometric area of theworking electrode. The solution was deaerated by purging a high-purity N2 gas (99.999%) throughout the test. All tests were carriedout at 25 ± 1 ◦C. Each test was repeated five times and the standarddeviation of the obtained results was calculated and shown as errorbar in the figures.

3. Results and discussion

Fig. 2 shows the SEM images of the surface morphologies of thePt particles prepared by pulsed electrodeposition under various tlranging from 1 to 0.01 s. The bright dots in the images refer to thedeposited Pt particles. It is clear that the surface morphology of thedeposited Pt particles on the ITO substrate is strongly dependenton the tl. When the tl is 1 s, the Pt particles on the ITO surface arefeatured with a flower-like morphology (Fig. 2a). The magnifiedimage indicates that such flower-like Pt particle actually consistsof a large number of nanosheets (Fig. 2b). When the tl decreasesto 0.5 s, dispersed Pt nanosheets are formed on the surface of ITO(Fig. 2c and d). As the tl further reduces to 0.1 and 0.05 s, Pt particleswith prickly surface are formed on the ITO substrate (Fig. 2e–h).When the tl is 0.01 s, Pt particles are characterized by a spherical-like morphology with a smooth surface (Fig. 2i and j).

During the electrodeposition process, the mass transfer of Ptions from the bulk solution through the diffusive layer toward theelectrode (diffusion process) and the reduction reaction on theelectrode (activation process) coexist [32]. For the pulsed elec-trodeposition in the present work, the reduction of Pt ions andthe following nucleation and growth of Pt nuclei occur during thecathodic half-cycle of the pulsed electrodeposition when a lowcathode potential of −1 V(MSE) is applied. Lower potential pulseduration tl plays a key role in determining the competitive effectsbetween the diffusion and activation processes, leading to differ-ent surface morphologies of the Pt deposits. During the cathodichalf-cycle of the electrodeposition, Pt ions are consumed due to thereduction process while diffusion of Pt ions to the electrode com-pensates the depletion. When the Pt ion consumption rate is higherthan the diffusion rate, a Pt ion depletion layer is formed, affecting

the growth of Pt nuclei [20]. During the anodic half-cycle, the con-sumed Pt ions at the electrode surface are replenished. Thus, theanodic half-cycle would decrease the thickness or even eliminatethe Pt depletion layer. This strongly facilitates the Pt ion transport,

166 J. Liu et al. / Electrochimica Acta 100 (2013) 164– 170

Fig. 2. SEM images of the Pt/ITO electrodes fabricated at the different lower potential pulse duration tl of (a) 1 s, (c) 0.5 s, (e) 0.1, (g) 0.05 s, (i) 0.01 s. The images of (b), (d),(f), (h) and (j) are the magnification images of (a), (c), (e), (g) and (i), respectively.

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nd enables a low degree of mass transfer limitations. At the longerl of 1 and 0.5 s, the consumed Pt ions cannot be timely compen-ated. As a result, the Pt electrodepositing process is controlled byhe diffusion process. In this case, the Pt nuclei tend to grow intoD planer structure, leading to the formation of flower-like andanosheet-like morphologies. The edges of the sheet grow much

aster than other parts (Fig. 2b and d). When the value of tl is loweri.e., 0.1 and 0.05 s), the consumed Pt ions can be partially com-ensated. The Pt particles are characterized by prickly morphologyFig. 2f and h), which is the characteristic with a mixed activationnd diffusion controlled process. At the short tl of 0.01 s, the con-umed Pt ions can be timely supplied during the anodic half-cycle.he growth of Pt deposits is dominated by the activation controlrocess and the formed Pt particles exhibit smooth spherical mor-hology (Fig. 2j), which is in agreement with the previous work32].

Fig. 3 shows the XRD patterns of the Pt particles on the ITOrepared by pulsed electrodeposition with different tl. The peaksround 39.8◦, 46.5◦, 67.6◦ and 81.5◦ are assigned to the diffrac-ion peaks of crystal faces Pt(1 1 1), Pt(2 0 0), Pt(2 2 0) and Pt(3 1 1),espectively. It is seen that all the electrodeposited Pt particles onTO substrate show polycrystalline structure without exhibitingny preferential orientation.

For assessing the electrocatalytic activity of the Pt particlesn the ITO fabricated at various tl for methanol oxidation, thet/ITO electrodes were tested by the cyclic voltammograms (CVs)n 0.5 mol L−1 H2SO4 solution containing 1 mol L−1 CH3OH. The CVsf Pt electrocatalysts fabricated at various tl are shown in Fig. 4,nd the current is normalized by the Pt loading. In the forwardranch, the oxidation current peak observed around 0.4 V (MSE)

s associated with the hydrogenation of methanol. In the reverseranch, the oxidation peak at about 0.15 V (MSE) is related to theemoval of the incompletely oxidized carbonaceous species formedn the forward scan [41–43]. Obviously, the pulsed electrodeposi-ion parameter, i.e., tl, has a strong influence on the value of theeak current of the prepared Pt electrocatalysts on the ITO forethanol oxidation. The Pt electrocatalysts fabricated at tl of 1 and

.5 s have much higher values of the oxidation peak current (0.39nd 0.45 mA �g−1) compared to the Pt electrocatalyst prepared at tlf 0.01 s (0.12 mA �g−1). The peak current (0.20 and 0.26 mA �g−1)

f the Pt electrocatalysts prepared at tl of 0.1 and 0.05 s rank inhe middle. In addition, the onset potentials of the Pt electrocat-lysts fabricated at tl of 1 and 0.5 s (−0.079 and −0.092 V (MSE))

ig. 3. XRD patterns of the Pt/ITO electrodes fabricated at the different lower poten-ial pulse duration tl .

Fig. 4. CVs measured on the Pt/ITO electrodes fabricated at the different tl in0.5 mol L−1 H2SO4 solution containing 1 mol L−1 CH3OH at 0.05 V s−1.

are markedly lower than that of the Pt electrocatalysts preparedby tl between 0.1 and 0.01 s (−0.007 to 0.014 V (MSE)). Further-more, it is worth noticing that the Pt electrocatalysts prepared attl of 1 and 0.5 s show much higher value of the peak current thanthe commercial Pt catalysts reported in previous literature (about0.08–0.24 mA �g−1) [44–46]. The above results indicate that the Ptelectrocatalysts fabricated at tl of 1 and 0.5 s have much higher elec-trocatalytic activities for methanol oxidation, which will be furtherdiscussed in the following part.

The electrocatalytic activity of the Pt/ITO electrocatalysts is eval-uated by the charge density required for the methanol oxidationreaction (QMOR, mC cm−2). The value of QMOR is determined fromthe area integrated under the methanol oxidation current peak inCV [33]. The mass specific activity (MA) of the Pt/ITO electrodesfor the methanol oxidation can be determined by QMOR/LPt, whereLPt is the amount of deposited Pt (�g cm−2). Fig. 5 shows the MAexpressed as QMOR/LPt of Pt/ITO electrocatalysts deposited at var-ious tl. It is seen that the electrocatalytic activity of the Pt/ITO

electrocatalysts for methanol oxidation strongly depends on the tlof the pulsed electrodeposition. For example, the MA of the Pt/ITOelectrocatalysts prepared at longer tl of 1 and 0.5 s ranges from

Fig. 5. The histogram of MA of the Pt/ITO electrodes fabricated at different lowerpotential pulse duration tl for methanol oxidation.

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.8 to 2.2 mC �g−1, which is nearly 4–5 times higher than that ofhe Pt electrocatalysts deposited at short tl of 0.01 s. According tohe morphological observations (Fig. 2), the influence of the tl onhe electrocatalytic activity of the Pt/ITO electrocatalysts is asso-iated with the morphological change of the Pt particles. Pulsedlectrodeposition with a relatively long tl of 1 and 0.5 s result inhe Pt particles with a flower-like structure (Fig. 2b) and dispersedt nanosheets (Fig. 2d) respectively. These morphological featuresontribute to high electrocatalytic activities. At the short tl of 0.01 s,he formed Pt particles on the ITO are featured with sphericalarticle with a larger size, which have the lowest electrocatalyticctivity.

To understand the effect of the morphological feature on thelectrocatalytic activity of the Pt/ITO electrocatalysts, the elec-rochemically active surface area (ECSA) as a function of tl isnvestigated. The ECSA of the prepared Pt particles on the ITO isetermined by measurements of CV in N2-saturated 0.5 mol L−1

2SO4. Fig. 6 shows the CVs measured on the Pt electrocatalystsrepared by the pulsed electrodeposition at various tl, and the cur-ent density is normalized by the Pt loading. The voltammetricrofile of the Pt/ITO electrocatalysts is similar to that of the typicalolycrystalline pure Pt, which has three well-defined character-

stic potential regions: the hydrogen adsorption and desorptionegions (−0.6 to −0.35 V (MSE)), double layer region (−0.35 to0.2 V (MSE)) and the formation and reduction of Pt oxide (−0.2

o 0.6 V (MSE)) [47]. It is also seen that the Pt particles deposited atonger tl (i.e., 1 and 0.5 s) on the ITO shows a much higher hydrogendsorption/desorption current density while the Pt particles pre-ared at short tl of 0.01 s has the lowest current density, indicatinghe former have a much larger SSA.

The ECSA (cm2 cm−2) of the Pt/ITO electrocatalysts is calculatedrom CV by [48]:

CSA = QH

Q 0H

(1)

here QH is the charge associated with the hydrogen desorptionmC cm−2), Q 0

H is the specific charge required for a hydrogen mono-ayer on Pt (0.21 mC cm−2) [49]. The QH value for the individualt/ITO electrocatalyst can be calculated by integrating the areaorresponding to the hydrogen desorption after subtracting the

ontribution of the double-charge layer. Furthermore, the ECSA isormalized by the amount of Pt loading in electrocatalysts, which isefined as specific active surface area (SSA, cm2 �g−1). Fig. 7 shows

ig. 6. CVs measured on the Pt/ITO electrodes fabricated at different tl in N2-aturated 0.5 mol L−1 H2SO4 solution at 0.05 V s−1.

Fig. 7. The histogram of SSA of the Pt/ITO electrodes fabricated at different tl formethanol oxidation.

the calculated SSA of the Pt/ITO electrocatalysts deposited at var-ious tl. It is seen that the Pt particles deposited at tl of 1 and 0.5 shave higher SSA, followed by the Pt particles prepared at tl of 0.1and 0.05 s and the Pt particles prepared at short tl of 0.01 s hasthe lowest SSA. This suggests that the SSA of the Pt particles onthe ITO decreases as the morphology of Pt particles changes fromsheet-like morphology to smooth spherical one. Since the electro-catalytic reaction occurs on the electrochemically active sites ofthe electrocatalysts, the larger SSA of the flower-like Pt particles(Fig. 2b) and dispersed Pt nanosheets (Fig. 2d) contributes to theirhigher electrocatalytic activities.

Furthermore, the MA of the electrocatalyst can be generallyexpressed as [50]:

MA = SSA × SA (2)

where SA is the specific activity (mC cm−2), which is defined aselectrocatalytic activity normalized by the ECSA. Fig. 8 shows the

tl. It is interesting to note that the SA is also dependent on thetl. The flower-like Pt particles obtained at tl of 1 s and dispersedPt nanosheets deposited at tl of 0.5 s have higher SA, and the

Fig. 8. The histogram of SA of Pt/ITO electrodes fabricated at different tl for methanoloxidation.

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ower-like and prickly Pt particles prepared at tl of 0.1 s and 0.05 slso possess higher SA than the smooth spherical Pt particles pre-ared at tl of 0.01 s. Therefore, the much improved MA of theower-like Pt particles (Fig. 2b) or dispersed Pt nanosheets (Fig. 2d)

s not only due to its larger SSA but also due to its higher SA. Gen-rally, the SA of the electrocatalysts depends on many factors suchs the preferential crystallographic orientation and surface mor-hology. In this work, irrespective of the morphologies, all the Ptarticles on the ITO appear to be polycrystalline structure and doot show any preferential orientation (Fig. 3). Therefore, the muchnhanced SA of the flower-like Pt particles and the dispersed Ptanosheets does not come from the contribution of the crystallinetructure. From the SEM images of the prepared Pt particles on theTO (Fig. 2), it can be seen that there are many protruding tipsr edges on the surface of the flower-like and nanosheet-like Ptarticles, compared with the surface of the smooth spherical parti-les. This could greatly contribute to the mass transport during theeaction, leading to the higher SA.

. Conclusions

The Pt particle electrocatalysts were prepared by the pulsedlectrodeposition on the ITO surface. The surface morphology andhe electrocatalytic activity of the deposited Pt for the methanolxidation are strongly dependent on the lower potential pulseuration (tl) of the pulsed electrodeposition. With the decreasef the tl, the surface morphology of the Pt particles changes fromower-, nanosheet-like morphology prepared at tl of 1 and 0.5 so prickly morphology obtained at tl of 0.1 and 0.05 s and finallyo smooth spherical morphology deposited at tl of 0.01 s. Further-

ore, the surface morphology of the Pt particles on the ITO playsn important role in determining the electrocatalytic activity ofhe Pt electrocatalysts for methanol oxidation. The flower- andanosheet-like Pt particles on the ITO possess much higher MA forhe methanol oxidation, followed by the Pt particles with pricklyurface while the smooth spherical Pt particles have the lowest MA.n particular, the dispersed Pt nanosheets prepared at tl of 0.5 sas the highest MA. The much improved MA of the dispersed Ptanosheets is attributed not only to the large ECSA achieved, butlso to the high electrocatalytic activity per unit ECSA (SA) relatedo its special morphology.

cknowledgements

The authors thank Drs. Y.J. Zhou, S. Xu and W. Li in the Instru-ental Analysis Center of Shanghai Jiao Tong University for the

CP and SEM analysis. This work was supported by the Nationalcience Foundation for Distinguished Young Scholars of China51125016), and partially supported by “Chen Guang” project sup-orted by Shanghai Municipal Education Commission and Shanghaiducation Development Foundation (11CG12), Shanghai Jiao Tongniversity (IPP6090, IPP6093 and S050ITP5011).

eferences

[1] S. Cattarin, M. Musiani, Electrosynthesis of nanocomposite materials for elec-trocatalysis, Electrochimica Acta 52 (2007) 2796.

[2] M.C. Daniel, D. Astruc, Gold nanoparticles: assembly, supramolecular chem-istry, quantum-size-related properties, and applications toward biology,catalysis, and nanotechnology, Chemical Reviews 104 (2004) 293.

[3] B. Ballarin, M.C. Cassani, E. Scavetta, D. Tonelli, Self-assembled gold nanopar-ticles modified ITO electrodes: the monolayer binder molecule effect,Electrochimica Acta 53 (2008) 8034.

[4] B. Ballarin, M. Gazzano, D. Tonelli, Effects of different additives on bimetallicAu–Pt nanoparticles electrodeposited onto indium tin oxide electrodes, Elec-

trochimica Acta 55 (2010) 6789.

[5] L. Rassaei, E. Vigil, R.W. French, M.F. Mahon, R.G. Compton, F. Marken, Effectsof microwave radiation on electrodeposition processes at tin-doped indiumoxide (ITO) electrodes, Electrochimica Acta 54 (2009) 6680.

[

a 100 (2013) 164– 170 169

[6] K. Endo, K. Nakamura, Y. Katayama, T. Miura, Pt–Me (Me = Ir, Ru, Ni) binaryalloys as an ammonia oxidation anode, Electrochimica Acta 49 (2004) 2503.

[7] S.G. Ramos, M.S. Moreno, G.A. Andreasen, W.E. Triaca, Facetted platinum elec-trocatalysts for electrochemical energy converters, International Journal ofHydrogen Energy 35 (2010) 5925.

[8] S. Le Vot, L. Roué, D. Bélanger, Electrodeposition of iridium onto glassy carbonand platinum electrodes, Electrochimica Acta 59 (2012) 49.

[9] E. Moran, C. Cattaneo, H. Mishima, B.A. López de Mishima, S.P. Silvetti, J.L.Rodriguez, E. Pastor, Ammonia oxidation on electrodeposited Pt–Ir alloys, Jour-nal of Solid State Electrochemistry 12 (2008) 583.

10] K. Yao, Y.F. Cheng, Fabrication by electrolytic deposition of Pt–Ni electrocat-alyst for oxidation of ammonia in alkaline solution, International Journal ofHydrogen Energy 33 (2008) 6681.

11] D.S. Kim, E.F.A. Zeid, Y.T. Kim, Additive treatment effect of TiO2 as supports forPt-based electrocatalysts on oxygen reduction reaction activity, ElectrochimicaActa 55 (2010) 3628.

12] L.P. Wang, W. Mao, D.D. Ni, J.W. Di, Y. Wu, Y.F. Tu, Direct electrodeposition ofgold nanoparticles onto indium/tin oxide film coated glass and its applicationfor electrochemical biosensor, Electrochemistry Communications 10 (2008)673.

13] B. Ballarin, M.C. Cassani, C. Maccato, A. Gasparotto, RF-sputtering preparationof gold-nanoparticle-modified ITO electrodes for electrocatalytic applications,Nanotechnology 22 (2011) 275711.

14] D.H. Dahanayaka, J.X. Wang, S. Hossain, L.A. Bumm, Optically transparent Au{1 1 1} substrates: flat gold nanoparticle platforms for high-resolution scanningtunneling microscopy, Journal of the American Chemical Society 128 (2006)6052.

15] A.E. Kasmi, M.C. Leopold, R. Galligan, R.T. Robertson, S.S. Saavedra, K.E. Kacemi,E.F. Bowden, Adsorptive immobilization of cytochrome c on indium/tin oxide(ITO): electrochemical evidence for electron transfer-induced conformationalchanges, Electrochemistry Communications 4 (2002) 177.

16] J.D. Zhang, M. Oyama, Gold nanoparticle arrays directly grown on nano-structured indium tin oxide electrodes: characterization and electroanalyticalapplication, Analytica Chimica Acta 540 (2005) 299.

17] G. Chang, J.D. Zhang, M. Oyama, K. Hirao, Silver-nanoparticle-attached indiumtin oxide surfaces fabricated by a seed-mediated growth approach, Journal ofPhysical Chemistry B 109 (2005) 1204.

18] G. Chang, M. Oyama, K. Hirao, In situ chemical reductive growth of platinumnanoparticles on indium tin oxide surfaces and their electrochemical applica-tions, Journal of Physical Chemistry B 110 (2006) 1860.

19] B. Ballarin, M. Gazzano, E. Scavetta, D. Tonelli, One-step electrosynthesis ofbimetallic Au–Pt nanoparticles on indium tin oxide electrodes: effect of thedeposition parameters, Journal of Physical Chemistry C 113 (2009) 15148.

20] J. Liu, W.B. Hu, C. Zhong, Y.F. Cheng, Surfactant-free electrochemical synthesisof hierarchical platinum particle electrocatalysts for oxidation of ammonia,Journal of Power Sources 223 (2013) 165.

21] J. Liu, C. Zhong, Y. Yang, Y.T. Wu, A.K. Jiang, Y.D. Deng, Z. Zhang, W.B. Hu, Elec-trochemical preparation and characterization of Pt particles on ITO substrate:Morphological effect on ammonia oxidation, International Journal of HydrogenEnergy 37 (2012) 8981.

22] J.D. Zhang, M. Oyama, Gold nanoparticle-attached ITO as a biocompatiblematrix for myoglobin immobilization: direct electrochemistry and cataly-sis to hydrogen peroxide, Journal of Electroanalytical Chemistry 577 (2005)273.

23] I.V. Kityk, J. Ebothe, I. Fuks-Janczarek, A.A. Umar, K. Kobayashi, M. Oyama, B.Sahraoui, Nonlinear optical properties of Au nanoparticles on indium–tin oxidesubstrate, Nanotechnology 16 (2005) 1687.

24] R.N. Goyal, M. Oyama, A. Tyagi, Simultaneous determination of guanosine andguanosine-5′-triphosphate in biological sample using gold nanoparticles mod-ified indium tin oxide electrode, Analytica Chimica Acta 581 (2007) 32.

25] P. Kannan, S. Sampath, S.A. John, Direct growth of gold nanorods on gold andindium tin oxide surfaces: spectral, electrochemical, and electrocatalytic stud-ies, Journal of Physical Chemistry C 114 (2010) 21114.

26] I. Zudans, J.R. Paddock, H. Kuramitza, A.T. Maghasia, C.M. Wansapuraa, S.D.Conklina, N. Kavala, T. Shtoykoa, D.J. Monka, S.A. Bryanb, T.L. Hublerb, J.N.Richardsonc, C.J. Seliskara, W.R.J. Heinemana, Electrochemical and optical eval-uation of noble metal- and carbon-ITO hybrid optically transparent electrodes,Electroanalytical Chemistry 565 (2004) 311.

27] D. Vu Ca, L.S. Sun, J.A. Cox, Optimization of the dispersion of gold and platinumnanoparticles on indium tin oxide for the electrocatalytic oxidation of cysteineand arsenite, Electrochimica Acta 51 (2006) 2188.

28] L. Tian, Y.J. Qi, B.B. Wang, Electrochemical preparation and structural charac-terization of platinum thin film on a polypyrrole film modified ITO electrode,Journal of Colloid and Interface Science 333 (2009) 249.

29] Y. Li, G.Q. Shi, Electrochemical growth of two-dimensional gold nanostructureson a thin polypyrrole film modified ITO electrode, Journal of Physical ChemistryB 109 (2005) 23787.

30] J.Y. Wang, P. Diao, D.F. Zhang, M. Xiang, Q. Zhang, Electrochemical sensing ofCO by gold particles electrodeposited on indium tin oxide substrate, Electro-chemistry Communications 11 (2009) 1069.

31] H.M. Zhang, W.Q. Zhou, Y.K. Du, P. Yang, C.Y. Wang, One-step electrodeposition

electro-oxidation, Electrochemistry Communications 12 (2010) 882.32] C. Zhong, W.B. Hu, Y.F. Cheng, On the essential role of current density in electro-

catalytic activity of the electrodeposited platinum for oxidation of ammonia,Journal of Power Sources 196 (2011) 8064.

1 ica Act

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

70 J. Liu et al. / Electrochim

33] C. Paoletti, A. Cemmi, L. Giorgi, R. Giorgi, L. Pilloni, E. Serra, M. Pasquali,Electro-deposition on carbon black and carbon nanotubes of Pt nanostructuredcatalysts for methanol oxidation, Journal of Power Sources 183 (2008) 84.

34] H. Natter, R. Hempelmann, Tailor-made nanomaterials designed by electro-chemical methods, Electrochimica Acta 49 (2003) 51.

35] Y. Song, Y.T. Ma, Y. Wang, J.W. Di, Y.F. Tu, Electrochemical deposition ofgold–platinum alloy nanoparticles on an indium tin oxide electrode and theirelectrocatalytic applications, Electrochimica Acta 55 (2010) 4909.

36] J.W. Wang, L.P. Wang, J.W. Di, Y.F. Tu, Electrodeposition of gold nanoparticleson indium/tin oxide electrode for fabrication of a disposable hydrogen peroxidebiosensor, Talanta 77 (2009) 1454.

37] J.J. Jow, S.W. Yang, H.R. Chen, M.S. Wu, T.R. Ling, T.Y. Wei, Co-electrodepositionof Pt–Ru electrocatalysts in electrolytes with varying compositions by a double-potential pulse method for the oxidation of MeOH and CO, International Journalof Hydrogen Energy 34 (2009) 665.

38] F. Alcaide, Ó. Miguel, H.J. Grande, New approach to prepare Pt-based hydrogendiffusion anodes tolerant to CO for polymer electrolyte membrane fuel cells,Catalysis Today 116 (2006) 408.

39] T. Kessler, A.M. Castro Luna, W.E. Triaca, Methanol electrooxidation on Pt–Rucatalysts dispersed in conducting polyaniline films, Portugaliae ElectrochimicaActa 22 (2004) 361.

40] M.M.E. Duarte, A.S. Pilla, J.M. Sieben, C.E. Mayer, Platinum particles electrode-

position on carbon substrates, Electrochemistry Communications 8 (2006) 159.

41] N. Soin, S.S. Roy, T.H. Lim, J.A.D. McLaughlin, Microstructural and electrochem-ical properties of vertically aligned few layered graphene (FLG) nanoflakes andtheir application in methanol oxidation, Materials Chemistry and Physics 129(2011) 1051.

[

a 100 (2013) 164– 170

42] Y.J. Li, W. Gao, L. Ci, C. Wang, P.M. Ajayan, Catalytic performance of Pt nanopar-ticles on reduced graphene oxide for methanol electro-oxidation, Carbon 48(2010) 1124.

43] Y.H. Lin, X.L. Cui, C.H. Yen, C.M. Wai, PtRu/carbon nanotube nanocompositesynthesized in supercritical fluid: a novel electrocatalyst for direct methanolfuel cells, Langmuir 21 (2005) 11474.

44] J.W. Guo, T.S. Zhao, J. Prabhuram, C.W. Wong, Preparation and the phys-ical/electrochemical properties of a Pt/C nanocatalyst stabilized by citricacid for polymer electrolyte fuel cells, Electrochimica Acta 50 (2005)1973.

45] A.X. Yin, X.Q. Min, W. Zhu, H.S. Wu, Y.W. Zhang, C.H. Yan, Multiply twinnedPt–Pd nanoicosahedrons as highly active electrocatalysts for methanol oxida-tion, Chemical Communications 48 (2012) 543.

46] S. Guo, S. Dong, E. Wang, Three-dimensional Pt-on-Pd bimetallic nanodendritessupported on graphene nanosheet: facile synthesis and used as an advancednanoelectrocatalyst for methanol oxidation, ACS Nano 4 (2009) 547.

47] N.M. Markovic, P.N. Ross, Surface science studies of model fuel cell electrocat-alysts, Surface Science Reports 45 (2002) 117.

48] F. Gloaguen, J.M. Leger, C. Lamy, A. Marmann, U. Stimming, R. Vogel, Plat-inum electrodeposition on graphite: electrochemical study and STM imaging,Electrochimica Acta 44 (1999) 1805.

49] E. Antolini, L. Giorgi, A. Pozio, E. Passalacqua, Influence of Nafion loading in the

catalyst layer of gas-diffusion electrodes for PEFC, Journal of Power Sources 77(1999) 136.

50] E. Antolini, J.J. Perez, The renaissance of unsupported nanostructured catalystsfor low-temperature fuel cells: from the size to the shape of metal nanostruc-tures, Journal of Materials Science 46 (2011) 4435.