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PSS-GN}n multilayer films and their electrocatalytic activity regarding methanol oxidation
Journal of Colloid and Interface Science 393 (2013) 300–305
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films and their electrocatalytic activity regarding methanol oxidation Xiaomei Huang, Zhongshui Li, Xiaofeng Zhang, Xiaolei He, Shen Lin ⇑ College of Chemistry & Chemical Engineering, Fujian Normal University, Fuzhou 350007, China Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, Fujian, China
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Article history: Received 9 August 2012 Accepted 26 October 2012 Available online 8 November 2012 Keywords: Functionalized graphene Layer-by-layer self-assembly Pt nanoclusters Electrocatalytic oxidation Methanol
a b s t r a c t The stable aqueous dispersion solutions of polymer-modified graphene were prepared by reduction with hydrazine hydrate in situ from exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The multilayer films consisting of PDDA-GN and PSS-GN were fabricated on the substrate by layer-by-layer self-assembly technique and characterized by ultraviolet–visible spectroscopy (UV–vis). The multilayer films were used as a novel catalyst support for electrodeposition of Pt nanoparticle clusters in situ. X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), and X-ray diffraction (XRD) analysis demonstrated that Pt particles had been immobilized on the surface of {PDDA-GN/PSS-GN}n multilayer films. Cyclic voltammetry and chronoamperometric curves were used to study electrocatalytic activity of Pt/{PDDA-GN/PSS-GN}n multilayer films regarding methanol oxidation. The results indicated good electrocatalytic activity of the titled multilayer composites toward methanol oxidation in the 0.5 M H2SO4. Ó 2012 Elsevier Inc. All rights reserved.
1. Introduction Direct methanol fuel cell (DMFC) has received much attention in the past few years due to its several advantages such as high power density, low pollutant emission, and abundance of methanol as a fuel [1]. Up to now, platinum is still a good catalyst for methanol oxidation [2,3]. However, pure Pt catalyst is expensive. In addition, methanol anodic oxidation intermediate absorption and accumulation on the Pt surface cause catalyst poisoning and deactivation and reduce the electrocatalytic activity of electrodes, limiting the performance of DMFC [4]. Consequently, decreasing the dosage of Pt and enhancing the catalytic efficiency and stability are still a very important issue in DMFC research. Up to date, many researchers have focused on the development of Pt-based binary [5], ternary [6], and even quaternary [7] alloys catalysts. Although each of the approaches has its own beneficial characteristics, they are also too expensive to practical application. Thus, many efforts have been directed toward searching for less expensive materials and explored new catalyst supports [8–10]. Graphene (GN), two-dimensional honeycomb lattice composing a single layer of bonded-sp2 carbons, has been attracting more attention in recent years due to its superior electric conductivities,
⇑ Corresponding author at: College of Chemistry & Chemical Engineering, Fujian Normal University, Fuzhou 350007, China. Fax: +86 591 22867399. E-mail address: [email protected] (S. Lin). 0021-9797/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2012.10.058
strong mechanical strength, high specific surface area, high electron mobility, and so on [11,12]. By reason of its unique properties, it has been widely used in nanocomposites [13], electronics [14], sensors [15], catalysis [8], and energy storage [16]. Moreover, graphene as a catalyst support has incurred intense interests in fuel cell applications [10]. And Pt particles supported on the graphene seem to be less susceptible to CO poisoning than those deposited onto traditional carbon supports [8]. Unfortunately, strong p–p stacking interaction between the GN sheets lead to its irreversible agglomerates, which will not only ruin the advantage of high surface area of graphene, but also obstruct the dispersion of Pt particles on GN [10]. An enormous amount of efforts have been concerning on covalent or noncovalent methods to functionalize GN in order to obtain solution-processable GN [12,17–20], which make it possible for controllably fabricating multicomponent hybrid films by sequential selfassembly with other oppositely charged nanomaterials. The layer-by-layer self-assembled method has been proven to be a promising method for fabricating ultrathin multilayer films [21–23]. It was successfully applied to charged organic polymers, nanoparticles, and other inorganic materials [24–26]. In this work, two stable aqueous dispersion functionalized GNs (PDDA-GN and PSS-GN) were prepared by the reduction of exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The functionalized GNs are positively or negatively charged, respectively, which are suitable to assemble multilayer composite
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films by electrostatic layer-by-layer absorption. Although a few studies on functionalized GN for the preparation of ultrathin multilayer films have been presented [27–29], the construction of multilayer systems composed of PDDA-GN and PSS-GN will be a new attempt. Most importantly, the thin films provide a novel graphene-based catalyst support for electrodeposition of Pt nanoclusters in situ. And Pt/{PDDA-GN/PSS-GN}n show good electrocatalytic activity regarding methanol oxidation and improved tolerance of CO.
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static electrodeposition in a 0.5 M H2SO4 solution containing 1.0 mM H2PtCl6 at 0.2 V for 600 s. DC-EC-1.0 electrochemical workstation was equipped with a digital coulometer (SPA-96BDAS-Y-A1) in order to determine the total charges consumed during Pt particles electrodeposition process. For the purpose of making a comparison, the electrodeposition of platinum on the surface of bare GCE and {PDDA/PSS}n multilayer films was also prepared under the same conditions. 3. Results and discussion
2. Experimental 3.1. UV–vis of {PDDA-GN/PSS-GN}n multilayer films 2.1. Materials Graphite ( 325mesh), poly (diallyldimethylammonium chloride) (PDDA, Mw 100,000–200,000, 20%), and poly (sodium 4-styrenesulfonate) (PSS, Mw 70,000) were purchased from Alfa Aesar. Potassium permanganate, hydrogen peroxide (30%), hydrazine hydrate, potassium persulfate, phosphorus pentoxide, phosphomolybdic acid, H2PtCl66H2O, H2SO4 (98%), acetone, and methanol were all purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used without further purification. Indium tin oxide (ITO) glass and quartz plate were purchased from Incole Union Technology Co., Ltd. (Tianjin, China). 2.2. Instrumentation Electrochemical experiments were carried out at DC-EC-1.0 electrochemical workstation (Changchun, China). A conventional three-electrode system was used, with composite films coated electrode as a working electrode, platinum column as a counter electrode, and Ag/AgCl (3 M KCl) as a reference electrode. Ultraviolet–visible absorption spectroscopy (UV–vis) was recorded on a quartz slide using a TU-1810DPC spectrophotometer (PUXI, Beijing, China). X-ray photoelectron spectroscopy (XPS) was performed at room temperature with monochromatic Al Ka radiation (1486.6 eV) using a Quantum 2000 system (Philips, USA). X-ray diffraction patterns (XRD) was obtained on X’pert Pro diffractometer (Philips, USA), using Cu Ka radiation. The 2h angular ranges from 10° to 85° were explored at a scan rate of 8° min 1. Images of field emission scanning electron microscope (FE-SEM) were observed on a JSM-7500F field emission scanning electron microanalyzer (JEOL, Japan).
The {PDDA-GN/PSS-GN}n multilayer films constructed from the positively charged PDDA-GN and the negatively charged PSS-GN were prepared by the electrostatic layer-by-layer self-assembly technique. The successful formation of the multilayer films is confirmed by the UV–vis absorption spectra of {PDDA-GN/PSS-GN}n multilayer films assembled on quartz substrates. As shown in Fig. 1, the absorption peaks at 195 nm and 226 nm are attributed to the aromatic ring in PSS [21,27], and the absorption peak at 260 nm is assigned to graphene nanoplatelets, indicating the successful introduction of graphene into multilayer films [32]. With the cycle numbers increasing, peak intensity is observed to increase, suggesting that a continuous growth of composite layers with each layer-by-layer deposition step. As illustrated in the inset of Fig. 1, the absorbance at 195 nm and 226 nm increased linearly with increasing bilayer number (n = 1, 3, 5, 7, 9), showing that uniform and homogeneous multilayer films have been fabricated. 3.2. XPS of Pt/{PDDA-GN/PSS-GN}n multilayer films The presence of C, N, O, Pt, and S in the Pt/{PDDA-GN/PSS-GN}2 multilayer films was verified by XPS, as indicated in Fig. 2A. In the XPS of C 1s (Fig. 2B), one dominant peak observed at 284.6 eV is attributed to graphitic carbon [27,33], and the other four weak peaks correspond to carbon atoms in different functional groups. Peaks at 286.3 eV and 287.1 eV are ascribed to the C in the CAO bonds and the carbonyl C (C@O), respectively [34]. And the peak at 285.2 eV is assigned to C in the CAS bonds of PSS-GN, and the peak at 285.8 eV is due to the C@N bonds of PSS-GN [27,35]. This implies that less oxygen existed in Pt/{PDDA-GN/ PSS-GN}2 multilayer films, due to the reduction after treatment with hydrazine in the presence of polyelectrolytes [28]. From
2.3. Preparation of {PDDA-GN/PSS-GN}n multilayer films Graphite oxide (GO) was prepared from purified natural graphite by the Hummers method [15,30]. PDDA-GN and PSS-GN were synthesized according to published procedures, respectively [22,31]. For layer-by-layer self-assembly, the substrates (ITO slide, quartz slide, and glass carbon electrode) were dipped in PDDA-GN aqueous solution (1 mg/mL) for 20 min, followed by rinsing with double distilled water and drying with high-purify nitrogen steam. Then, PDDA-GN adsorbed substrates were dipped in PSS-GN aqueous solution (1 mg/mL) for 20 min, rinsed with double distilled water, and dried with high-purify nitrogen steam. Thus, the bilayer film was obtained. By repeating previous process, the subsequent multilayer films (designated as {PDDA-GN/PSS-GN}n) were prepared. 2.4. Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films Pt particles were deposited in situ on the surface of {PDDA-GN/ PSS-GN}n multilayer films modified glass carbon electrode (GCE, 3 mm in diameter) or ITO electrode (4 mm in width) by potentio-
Fig. 1. UV–vis absorption spectra of {PDDA-GN/PSS-GN}n LBL assembled on quartz slide with different bilayer numbers: 1, 3, 5, 7, and 9 (from a to e). The inset shows the absorbance at 195 nm and 226 nm versus the number of bilayers.
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Fig. 2. XPS spectra of the Pt/{PDDA-GN/PSS-GN}2/ITO multilayer films: (A) full-spectra, (B) C 1s spectra, (C) N 1s spectra, and (D) Pt 4f spectra.
The surface morphologies of Pt on different films modified electrodes were characterized with FE-SEM. As shown in Fig. 4A, the Pt nanoparticles electrodeposited on bare ITO show itself irregular squares with average diameter 100–200 nm. Fig. 4B, D, and F display the surface morphologies of Pt/{n PDDA-GN/n 1 PSS-GN} (n = 1, 2, 3) with PDDA-GN as the outmost layer. As seen in Fig. 4B, the Pt nanoparticles are very small, with average diameter of about 20 nm, and a few nanoparticles aggregate. With the number of layers (n) extending from 1 to 3, Pt nanoparticles aggregate obviously, and the interesting cauliflower like Pt micro–nanoclusters consisting of small nanoparticles are formed. As illustrated in Fig. 4D, the diame-
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3.4. SEM of Pt/{PDDA-GN/PSS-GN}n multilayer films
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X-ray diffraction (XRD) patterns of the {2PDDA-GN/PSS-GN}/ITO (A) and Pt/{2PDDA-GN/PSS-GN}/ITO (B) multilayer films are shown in Fig. 3. The 2h values corresponding to the (22 2), (4 0 0), (4 4 0), and (6 2 2) crystal face diffraction peaks for ITO are 30.2°, 35.5°, 50.8°, and 60.3°, respectively [36]. However, as illustrated in Fig. 3B, it is easy to find four major peaks at about 40.4°, 46.8° 67.8°, and 81.9° besides the peaks for ITO, corresponding to the (1 1 1), (20 0), (22 0), and (31 1) planes of the face-centered cubic (fcc) structure of Pt, respectively (refer to ICDD PDF card no. 04-0802).
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3.3. XRD of Pt/{PDDA-GN/PSS-GN}n multilayer films
ters of these micro–nanoclusters range from 100 to 150 nm. The unique configuration can greatly increase the surface area of Pt clusters. The formation of the cauliflower like cluster structure is attributed to PDDA-GN surface with positively charged quaternary ammonium 2 functional groups, which could make PtCl6 ions easily diffuse into the surface of the multilayer films via the electrostatic interaction [25]. During the electrodeposited process, the quaternary ammonium provides binding sites for anchoring precursor metal ions or metal nanoparticles, resulting in the continuous formation of new nuclei [37]. The morphologies of Pt nanoparticles electrodeposited on {n PDDA-GN/n PSS-GN} (n = 1, 2) multilayer films can be observed
Intensity / a.u.
Fig. 2C, the peak at 401.7 eV is assigned to N of PDDA in the graphene sheets [33]. Pt 4f7/2 peak at 71.4 eV and Pt 4f5/2 peak at 74.8 eV are found in the Pt 4f binding energy region as given in Fig. 2D, which reveals that the deposited Pt nanoparticles are in zero valent state [10]. The XPS spectra show that Pt/{PDDAGN/PSS-GN}2 multilayer films have been assembled successfully.
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2 / degree Fig. 3. XRD patterns of the multilayer films: (A) {2PDDA-GN/PSS-GN}/ITO and (B) Pt/{2PDDA-GN/PSS-GN}/ITO.
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Fig. 4. FE-SEM images of (A) Pt/ITO, (B) Pt/{PDDA-GN}/ITO, (C) Pt/{PDDA- GN/PSS-GN}/ITO, (D) Pt/{2PDDA-GN/PSS-GN}/ITO, (E) Pt/{2PDDA-GN/2PSS- GN}/ITO, and (F) Pt/ {3PDDA-GN/2PSS-GN}/ITO, at 0.2 V for 600 s.
in Fig. 4C and E. As compared to that on {n PDDA-GN/n 1 PSS-GN} (Fig. 4D), Pt nanoparticles on {n PDDA-GN/n PSS-GN} also aggregate to form micro–nanoclusters, but their dispersion is poorer. The linear negatively charged polyelectrolyte PSS in the PSS-GN also offers large and uniformly distributed active sites for anchoring metal ions and metal nanoparticles, but mutually exclusive interaction between 2 PtCl6 ions and PSS-GN may be responsible for the poorer dispersion of Pt micro–nanoclusters. In summary, it can be demonstrated that the {PDDA-GN/PSS-GN}n multilayer films play a special function in the formation of Pt micro–nanoclusters. As we all know, the process
of electrodeposition involves two parts, seed formation and growth [9]. Actually, the characters of deposited substrates would affect these two processes. For the Pt nanoparticles deposited onto bare ITO surface, the Pt seeds firstly appear and then grow into Pt nanoparticles. In such case, the growth process should dominate, and finally, nanoparticles could be formed [9]. On the other hand, for Pt nanoclusters deposited onto {PDDA-GN/PSS-GN}n multilayer films in our case, Pt seeds form on the surface at the primary stage but these seeds do not grow into larger Pt nanoparticles. After that, these small Pt nanoparticles aggregate to form Pt nanoclusters [38].
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Fig. 5. (A) CVs of Pt/{PDDA-GN/PSS-GN}n/GCE multilayer films with different layers; (B) CVs of Pt/{2PDDA/PSS}/GCE (1), Pt/GCE (2), and Pt/{2PDDA-GN/PSS-GN}/GCE (3). Scan rate 100 mV s 1, in 0.5 M H2SO4 + 1 M CH3OH.
The electrochemical oxidation of methanol was investigated by cyclic voltammetry in the solution containing 0.5 M H2SO4 + 1 M CH3OH (Fig. 5). Fig. 5A displays CV behavior of the Pt/{PDDA-GN/ PSS-GN}n/GCE films with different layers. It can be found that there are two anodic peaks in all CV curves. The forward anodic peak current at about 0.65 V is attributed to the electrooxidation of methanol, and the backward peak current at about 0.4 V originates from the removal of incompletely oxidized intermediate carbonaceous species formed in the forward scan on the surface of the catalysts, mainly CO [39]. The forward anodic peak current of Pt/ {PDDA-GN}/GCE (curve 5) is 1.4-fold higher than that of Pt/{PSSGN}/GCE (curve 1). And the Pt/{2PDDA-GN/PSS-GN}/GCE electrode shows the highest peak current and the greatest negative shift of the forward peak potential and backward peak potential, which is the evidence of highest electrocatalytic activity. As a whole, Pt supported on {n PDDA-GN/n 1 PSS-GN} (n = 1, 2, 3) with PDDAGN as the outmost layer exhibits higher electrocatalytic activity than that on {n PDDA-GN/n PSS-GN} (n = 1, 2). This may be attributed to the excellent binding capability between the positively charged PDDA and graphene [34]. Furthermore, during the electro2 deposition process, PtCl6 anions easily diffuse into the surface of PDDA-GN to form cauliflower like Pt micro–nanoclusters [37], which results in different electrochemical surface area (ECSA). Fig. S1 shows the CV curves of the Pt/{n PDDA-GN/m PSS-GN}/ GCE electrocatalysts in 0.5 M H2SO4 aqueous solutions. As illustrated by integrating the hydrogen adsorption/desorption charges according to the CV curves, the Pt/{2PDDA-GN/PSS-GN} films possess a relatively higher ECSA than that of Pt/{PDDA-GN/PSS-GN}, which helps enhance the catalytic activity. In order to make a comparison, the electrochemical oxidation of methanol of Pt particles electrodeposited on {2PDDA/PSS} and bare GCE were also investigated. As indicated in Fig. 5B, it is clearly seen that the highest forward anodic peak current of 1.5 mA is obtained as regards Pt/ {2PDDA-GN/PSS-GN}/GCE, which is about 1.5 times and 3.8 times as high as that of the Pt/GCE (0.97 mA), and Pt/{2PDDA/PSS}/GCE (0.39 mA), respectively. Moreover, the enhanced activity of Pt/ {2PDDA-GN/PSS-GN}/GCE was also evidenced by a lower onset potential. Apparently, this difference is mainly caused by the graphene-based multilayer films, which not only have superior electric conductivities, but also provide a novel catalyst support to improve the dispersion of Pt particles. To further evaluate the catalytic activity and stability of different films modified electrode in methanol oxidation, chronoampe-
rometry experiments were carried out in 0.5 M H2SO4 and 1.0 M CH3OH solutions under a constant potential of 0.65 V for 800 s. As shown in Fig. 6, the currents decrease quickly at the beginning, possibly owing to the formation of intermediate species and some poisonous species, such as COads and CHOads during the methanol oxidation reaction [40]. Afterward, the currents diminish much more slowly and reach a quasi-stationary within 800 s. This can be tentatively ascribed to the presence of surface active impurities or anions in the electrolyte solution that could slowly adsorb onto the electrode surface during long-term experiments, thereby determining the loss of activity [40]. The stability of the different films modified electrode follows the order of Pt/{2PDDA-GN/PSSGN}/GCE > Pt/{2PDDA/PSS} > Pt/GCE, which is consistent with the results obtained from the CV curves of methanol electrooxidation. In addition, it is evident that Pt/{2PDDA-GN/PSS-GN}/GCE shows lower decay of current with time and a obviously higher quasi-stationary current. These results strongly suggest that Pt/{2PDDA-GN/ PSS-GN}/GCE have a better tolerance toward CO poisoning than the others [4]. The enhanced catalytic activity and stability may be owing to the polymer-modified graphene (PDDA-GN and PSS-GN) preserves the superior electric conductivities in the multilayer films, which can be proven by Nyquist plots of the electrochemical impedance spectrum (EIS) (Fig. S2). Usually, the semicircle diameter is equal to the electron-transfer resistance (Rct), which is af-
1.0 3.Pt/{2PDDA-GN/PSS-GN}/GCE 2. Pt/{2PDDA/PSS}/GCE
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Time/s Fig. 6. Chronoamperometric curves of the different films modified electrode: (1) Pt/ GCE, (2) Pt/{2PDDA/PSS}/GCE, (3) Pt/{2PDDA-GN/PSS-GN}/GCE in 0.5 M H2SO4 + 1 M CH3OH at 0.65 V for 800 s.
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fected obviously by the surface modification of the electrode. As shown in Fig. S2, Rct decreases with the introduction of {2PDDAGN/PSS-GN} multilayer films. This means that polymer-modified graphene helps enhance electron transfer obviously on the electrode interface. 4. Conclusion In summary, graphene was functionally modified by PDDA and PSS. The {PDDA-GN/PSS-GN}n multilayer films were prepared by LBL method and used as a new kind of catalyst support for preparation of Pt nanoparticles through the electrodeposition in situ. Most interestingly, electrochemical investigation indicated that the presence of functionalized graphene in the Pt/{PDDA-GN/PSSGN}n modified electrodes greatly enhanced catalytic activity and stability toward methanol oxidation. The scalable chemical synthesis of graphene and the convenient preparation of multilayer films also provide a cost benefit of the electrocatalysts. The results demonstrate a promising approach for the development of low-cost and high-performance Pt-based anode electrocatalysts in fuel cells. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 21171037) and the Natural Science Foundation of Fujian Province (No. 2011J0101). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2012.10.058. References [1] X.L. Li, A. Faghri, C. Xu, Int. J. Hydrogen Energy 35 (2010) 8690. [2] Y.-H. Cho, H.-S. Park, Y.-H. Cho, I.-S. Park, Y.-E. Sung, Electrochim. Acta 53 (2008) 5909. [3] S.P. Jiang, Z. Liu, H.L. Tang, M. Pan, Electrochim. Acta 51 (2006) 5721. [4] J.R.C. Salgado, F. Alcaide, G. Álvarez, L. Calvillo, M.J. Lázaro, E. Pastor, J. Power Sources 195 (2010) 4022. [5] H. Zhu, Z. Guo, X. Zhang, K. Han, Y. Guo, F. Wang, Z. Wang, Y. Wei, Int. J. Hydrogen Energy 37 (2012) 873.
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[6] Y.Z. Zhang, Y.E. Gu, S.X. Lin, J.P. Wei, Z.H. Wang, C.M. Wang, Y.L. Du, W.C. Ye, Electrochim. Acta 56 (2011) 8746. [7] K. Fatih, V. Neburchilov, V. Alzate, R. Neagu, H. Wang, J. Power Sources 195 (2010) 7168. [8] H.J. Huang, H.Q. Chen, D.P. Sun, X. Wang, J. Power Sources 204 (2012) 46. [9] P. Wang, F. Li, X. Huang, Y. Li, L. Wang, Electrochem. Commun. 10 (2008) 195. [10] Y.C. Xin, J.G. Liu, Y. Zhou, W.M. Liu, J.A. Gao, Y. Xie, Y. Yin, Z.G. Zou, J. Power Sources 196 (2011) 1012. [11] S. Guo, S. Dong, Chem. Soc. Rev. 40 (2011) 2644. [12] X. Huang, Z. Yin, S. Wu, X. Qi, Q. He, Q. Zhang, Q. Yan, F. Boey, H. Zhang, Small 7 (2011) 1876. [13] T. Kuila, S. Bose, A.K. Mishra, P. Khanra, N.H. Kim, J.H. Lee, Polym. Test. 31 (2012) 31. [14] M. Dragoman, D. Dragoman, Prog. Quantum Electron. 33 (2009) 165. [15] Q.O. Zeng, J.S. Cheng, L.H. Tang, X.F. Liu, Y.Z. Liu, J.H. Li, J.H. Jiang, Adv. Funct. Mater. 20 (2010) 3366. [16] L. Grande, V.T. Chundi, D. Wei, C. Bower, P. Andrew, T. Ryhänen, Particuology 10 (2012) 1. [17] H. Gu, Y.Y. Yu, X.Q. Liu, B. Ni, T.S. Zhou, G.Y. Shi, Biosens. Bioelectron. 32 (2012) 118. [18] S. Kamada, H. Nomoto, K. Fukuda, T. Fukawa, H. Shirai, M. Kimura, Colloid. Polym. Sci. 289 (2011) 925. [19] Z. Spitalsky, M. Danko, J. Mosnacek, Curr. Org. Chem. 15 (2011) 1133. [20] J.M. Bak, T. Lee, E. Seo, Y. Lee, H.M. Jeong, B.S. Kim, H.I. Lee, Polymer 53 (2012) 316. [21] Y. Fu, S.-J. Li, J. Xu, M. Yang, J.-D. Zhang, Y.-H. Jiao, J.-C. Zhang, K. Zhang, Y.-G. Jia, Langmuir 27 (2010) 672. [22] Z.P. Li, J.Q. Wang, X.H. Liu, S. Liu, J.F. Ou, S.R. Yang, J. Mater. Chem. 21 (2011) 3397. [23] G. Decher, J.D. Hong, J. Schmitt, Thin Solid Films 210–211 (1992) 831. [24] A. Kazemi, J. Lahann, M. Madani, N. Sharifi-Sanjani, A. Hasan-Kaviar, Polym. Sci. Ser. B Polym. Chem. 52 (2010) 571. [25] Z.S. Li, S. Lin, Z.L. Chen, Y.D. Shi, X.M. Huang, J. Colloid Interface Sci. 368 (2012) 413. [26] Y. Lvov, G. Decher, H. Moehwald, Langmuir 9 (1993) 481. [27] A. Rani, K.A. Oh, H. Koo, H.J. Lee, M. Park, Appl. Surf. Sci. 257 (2011) 4982. [28] J. Yang, Y. Zhou, L. Sun, N. Zhao, C. Zang, X. Cheng, Appl. Surf. Sci. 258 (2012) 5056. [29] J. Shen, Y. Hu, C. Li, C. Qin, M. Shi, M. Ye, Langmuir 25 (2009) 6122. [30] W.S. Hummers, R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. [31] J.-J. Shi, G.-H. Yang, J.-J. Zhu, J. Mater. Chem. 21 (2011) 7343. [32] Q.W. Tang, J.H. Wu, Q.H. Li, J.M. Lin, Polymer 49 (2008) 5329. [33] S.Y. Wang, D.S. Yu, L.M. Dai, D.W. Chang, J.B. Baek, Acs Nano 5 (2011) 6202. [34] B.M. Luo, X.B. Yan, S. Xu, Q.J. Xue, Electrochim. Acta 59 (2012) 429. [35] S. Stankovich, R.D. Piner, X. Chen, N. Wu, S.T. Nguyen, R.S. Ruoff, J. Mater. Chem. 16 (2006) 155. [36] Z.Y. Sun, J.B. He, A. Kumbhar, J.Y. Fang, Langmuir 26 (2010) 4246. [37] L. Qian, X. Yang, Talanta 74 (2008) 1649. [38] L. Qian, X. Yang, J. Phys. Chem. B 110 (2006) 16672. [39] F. Ren, R. Zhou, F. Jiang, W. Zhou, Y. Du, J. Xu, C. Wang, Fuel Cells 12 (2012) 116. [40] J. Prabhuram, T.S. Zhao, Z.X. Liang, R. Chen, Electrochim. Acta 52 (2007) 2649.
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films and their electrocatalytic activity regarding methanol oxidation Xiaomei Huang, Zhongshui Li, Xiaofeng Zhang, Xiaolei He, Shen Lin ⇑ College of Chemistry & Chemical Engineering, Fujian Normal University, Fuzhou 350007, China Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, Fujian, China
a r t i c l e
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Article history: Received 9 August 2012 Accepted 26 October 2012 Available online 8 November 2012 Keywords: Functionalized graphene Layer-by-layer self-assembly Pt nanoclusters Electrocatalytic oxidation Methanol
a b s t r a c t The stable aqueous dispersion solutions of polymer-modified graphene were prepared by reduction with hydrazine hydrate in situ from exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The multilayer films consisting of PDDA-GN and PSS-GN were fabricated on the substrate by layer-by-layer self-assembly technique and characterized by ultraviolet–visible spectroscopy (UV–vis). The multilayer films were used as a novel catalyst support for electrodeposition of Pt nanoparticle clusters in situ. X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), and X-ray diffraction (XRD) analysis demonstrated that Pt particles had been immobilized on the surface of {PDDA-GN/PSS-GN}n multilayer films. Cyclic voltammetry and chronoamperometric curves were used to study electrocatalytic activity of Pt/{PDDA-GN/PSS-GN}n multilayer films regarding methanol oxidation. The results indicated good electrocatalytic activity of the titled multilayer composites toward methanol oxidation in the 0.5 M H2SO4. Ó 2012 Elsevier Inc. All rights reserved.
1. Introduction Direct methanol fuel cell (DMFC) has received much attention in the past few years due to its several advantages such as high power density, low pollutant emission, and abundance of methanol as a fuel [1]. Up to now, platinum is still a good catalyst for methanol oxidation [2,3]. However, pure Pt catalyst is expensive. In addition, methanol anodic oxidation intermediate absorption and accumulation on the Pt surface cause catalyst poisoning and deactivation and reduce the electrocatalytic activity of electrodes, limiting the performance of DMFC [4]. Consequently, decreasing the dosage of Pt and enhancing the catalytic efficiency and stability are still a very important issue in DMFC research. Up to date, many researchers have focused on the development of Pt-based binary [5], ternary [6], and even quaternary [7] alloys catalysts. Although each of the approaches has its own beneficial characteristics, they are also too expensive to practical application. Thus, many efforts have been directed toward searching for less expensive materials and explored new catalyst supports [8–10]. Graphene (GN), two-dimensional honeycomb lattice composing a single layer of bonded-sp2 carbons, has been attracting more attention in recent years due to its superior electric conductivities,
⇑ Corresponding author at: College of Chemistry & Chemical Engineering, Fujian Normal University, Fuzhou 350007, China. Fax: +86 591 22867399. E-mail address: [email protected] (S. Lin). 0021-9797/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2012.10.058
strong mechanical strength, high specific surface area, high electron mobility, and so on [11,12]. By reason of its unique properties, it has been widely used in nanocomposites [13], electronics [14], sensors [15], catalysis [8], and energy storage [16]. Moreover, graphene as a catalyst support has incurred intense interests in fuel cell applications [10]. And Pt particles supported on the graphene seem to be less susceptible to CO poisoning than those deposited onto traditional carbon supports [8]. Unfortunately, strong p–p stacking interaction between the GN sheets lead to its irreversible agglomerates, which will not only ruin the advantage of high surface area of graphene, but also obstruct the dispersion of Pt particles on GN [10]. An enormous amount of efforts have been concerning on covalent or noncovalent methods to functionalize GN in order to obtain solution-processable GN [12,17–20], which make it possible for controllably fabricating multicomponent hybrid films by sequential selfassembly with other oppositely charged nanomaterials. The layer-by-layer self-assembled method has been proven to be a promising method for fabricating ultrathin multilayer films [21–23]. It was successfully applied to charged organic polymers, nanoparticles, and other inorganic materials [24–26]. In this work, two stable aqueous dispersion functionalized GNs (PDDA-GN and PSS-GN) were prepared by the reduction of exfoliated graphite oxides in the presence of poly (diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), respectively. The functionalized GNs are positively or negatively charged, respectively, which are suitable to assemble multilayer composite
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films by electrostatic layer-by-layer absorption. Although a few studies on functionalized GN for the preparation of ultrathin multilayer films have been presented [27–29], the construction of multilayer systems composed of PDDA-GN and PSS-GN will be a new attempt. Most importantly, the thin films provide a novel graphene-based catalyst support for electrodeposition of Pt nanoclusters in situ. And Pt/{PDDA-GN/PSS-GN}n show good electrocatalytic activity regarding methanol oxidation and improved tolerance of CO.
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static electrodeposition in a 0.5 M H2SO4 solution containing 1.0 mM H2PtCl6 at 0.2 V for 600 s. DC-EC-1.0 electrochemical workstation was equipped with a digital coulometer (SPA-96BDAS-Y-A1) in order to determine the total charges consumed during Pt particles electrodeposition process. For the purpose of making a comparison, the electrodeposition of platinum on the surface of bare GCE and {PDDA/PSS}n multilayer films was also prepared under the same conditions. 3. Results and discussion
2. Experimental 3.1. UV–vis of {PDDA-GN/PSS-GN}n multilayer films 2.1. Materials Graphite ( 325mesh), poly (diallyldimethylammonium chloride) (PDDA, Mw 100,000–200,000, 20%), and poly (sodium 4-styrenesulfonate) (PSS, Mw 70,000) were purchased from Alfa Aesar. Potassium permanganate, hydrogen peroxide (30%), hydrazine hydrate, potassium persulfate, phosphorus pentoxide, phosphomolybdic acid, H2PtCl66H2O, H2SO4 (98%), acetone, and methanol were all purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used without further purification. Indium tin oxide (ITO) glass and quartz plate were purchased from Incole Union Technology Co., Ltd. (Tianjin, China). 2.2. Instrumentation Electrochemical experiments were carried out at DC-EC-1.0 electrochemical workstation (Changchun, China). A conventional three-electrode system was used, with composite films coated electrode as a working electrode, platinum column as a counter electrode, and Ag/AgCl (3 M KCl) as a reference electrode. Ultraviolet–visible absorption spectroscopy (UV–vis) was recorded on a quartz slide using a TU-1810DPC spectrophotometer (PUXI, Beijing, China). X-ray photoelectron spectroscopy (XPS) was performed at room temperature with monochromatic Al Ka radiation (1486.6 eV) using a Quantum 2000 system (Philips, USA). X-ray diffraction patterns (XRD) was obtained on X’pert Pro diffractometer (Philips, USA), using Cu Ka radiation. The 2h angular ranges from 10° to 85° were explored at a scan rate of 8° min 1. Images of field emission scanning electron microscope (FE-SEM) were observed on a JSM-7500F field emission scanning electron microanalyzer (JEOL, Japan).
The {PDDA-GN/PSS-GN}n multilayer films constructed from the positively charged PDDA-GN and the negatively charged PSS-GN were prepared by the electrostatic layer-by-layer self-assembly technique. The successful formation of the multilayer films is confirmed by the UV–vis absorption spectra of {PDDA-GN/PSS-GN}n multilayer films assembled on quartz substrates. As shown in Fig. 1, the absorption peaks at 195 nm and 226 nm are attributed to the aromatic ring in PSS [21,27], and the absorption peak at 260 nm is assigned to graphene nanoplatelets, indicating the successful introduction of graphene into multilayer films [32]. With the cycle numbers increasing, peak intensity is observed to increase, suggesting that a continuous growth of composite layers with each layer-by-layer deposition step. As illustrated in the inset of Fig. 1, the absorbance at 195 nm and 226 nm increased linearly with increasing bilayer number (n = 1, 3, 5, 7, 9), showing that uniform and homogeneous multilayer films have been fabricated. 3.2. XPS of Pt/{PDDA-GN/PSS-GN}n multilayer films The presence of C, N, O, Pt, and S in the Pt/{PDDA-GN/PSS-GN}2 multilayer films was verified by XPS, as indicated in Fig. 2A. In the XPS of C 1s (Fig. 2B), one dominant peak observed at 284.6 eV is attributed to graphitic carbon [27,33], and the other four weak peaks correspond to carbon atoms in different functional groups. Peaks at 286.3 eV and 287.1 eV are ascribed to the C in the CAO bonds and the carbonyl C (C@O), respectively [34]. And the peak at 285.2 eV is assigned to C in the CAS bonds of PSS-GN, and the peak at 285.8 eV is due to the C@N bonds of PSS-GN [27,35]. This implies that less oxygen existed in Pt/{PDDA-GN/ PSS-GN}2 multilayer films, due to the reduction after treatment with hydrazine in the presence of polyelectrolytes [28]. From
2.3. Preparation of {PDDA-GN/PSS-GN}n multilayer films Graphite oxide (GO) was prepared from purified natural graphite by the Hummers method [15,30]. PDDA-GN and PSS-GN were synthesized according to published procedures, respectively [22,31]. For layer-by-layer self-assembly, the substrates (ITO slide, quartz slide, and glass carbon electrode) were dipped in PDDA-GN aqueous solution (1 mg/mL) for 20 min, followed by rinsing with double distilled water and drying with high-purify nitrogen steam. Then, PDDA-GN adsorbed substrates were dipped in PSS-GN aqueous solution (1 mg/mL) for 20 min, rinsed with double distilled water, and dried with high-purify nitrogen steam. Thus, the bilayer film was obtained. By repeating previous process, the subsequent multilayer films (designated as {PDDA-GN/PSS-GN}n) were prepared. 2.4. Preparation of Pt/{PDDA-GN/PSS-GN}n multilayer films Pt particles were deposited in situ on the surface of {PDDA-GN/ PSS-GN}n multilayer films modified glass carbon electrode (GCE, 3 mm in diameter) or ITO electrode (4 mm in width) by potentio-
Fig. 1. UV–vis absorption spectra of {PDDA-GN/PSS-GN}n LBL assembled on quartz slide with different bilayer numbers: 1, 3, 5, 7, and 9 (from a to e). The inset shows the absorbance at 195 nm and 226 nm versus the number of bilayers.
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Fig. 2. XPS spectra of the Pt/{PDDA-GN/PSS-GN}2/ITO multilayer films: (A) full-spectra, (B) C 1s spectra, (C) N 1s spectra, and (D) Pt 4f spectra.
The surface morphologies of Pt on different films modified electrodes were characterized with FE-SEM. As shown in Fig. 4A, the Pt nanoparticles electrodeposited on bare ITO show itself irregular squares with average diameter 100–200 nm. Fig. 4B, D, and F display the surface morphologies of Pt/{n PDDA-GN/n 1 PSS-GN} (n = 1, 2, 3) with PDDA-GN as the outmost layer. As seen in Fig. 4B, the Pt nanoparticles are very small, with average diameter of about 20 nm, and a few nanoparticles aggregate. With the number of layers (n) extending from 1 to 3, Pt nanoparticles aggregate obviously, and the interesting cauliflower like Pt micro–nanoclusters consisting of small nanoparticles are formed. As illustrated in Fig. 4D, the diame-
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X-ray diffraction (XRD) patterns of the {2PDDA-GN/PSS-GN}/ITO (A) and Pt/{2PDDA-GN/PSS-GN}/ITO (B) multilayer films are shown in Fig. 3. The 2h values corresponding to the (22 2), (4 0 0), (4 4 0), and (6 2 2) crystal face diffraction peaks for ITO are 30.2°, 35.5°, 50.8°, and 60.3°, respectively [36]. However, as illustrated in Fig. 3B, it is easy to find four major peaks at about 40.4°, 46.8° 67.8°, and 81.9° besides the peaks for ITO, corresponding to the (1 1 1), (20 0), (22 0), and (31 1) planes of the face-centered cubic (fcc) structure of Pt, respectively (refer to ICDD PDF card no. 04-0802).
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3.3. XRD of Pt/{PDDA-GN/PSS-GN}n multilayer films
ters of these micro–nanoclusters range from 100 to 150 nm. The unique configuration can greatly increase the surface area of Pt clusters. The formation of the cauliflower like cluster structure is attributed to PDDA-GN surface with positively charged quaternary ammonium 2 functional groups, which could make PtCl6 ions easily diffuse into the surface of the multilayer films via the electrostatic interaction [25]. During the electrodeposited process, the quaternary ammonium provides binding sites for anchoring precursor metal ions or metal nanoparticles, resulting in the continuous formation of new nuclei [37]. The morphologies of Pt nanoparticles electrodeposited on {n PDDA-GN/n PSS-GN} (n = 1, 2) multilayer films can be observed
Intensity / a.u.
Fig. 2C, the peak at 401.7 eV is assigned to N of PDDA in the graphene sheets [33]. Pt 4f7/2 peak at 71.4 eV and Pt 4f5/2 peak at 74.8 eV are found in the Pt 4f binding energy region as given in Fig. 2D, which reveals that the deposited Pt nanoparticles are in zero valent state [10]. The XPS spectra show that Pt/{PDDAGN/PSS-GN}2 multilayer films have been assembled successfully.
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2 / degree Fig. 3. XRD patterns of the multilayer films: (A) {2PDDA-GN/PSS-GN}/ITO and (B) Pt/{2PDDA-GN/PSS-GN}/ITO.
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Fig. 4. FE-SEM images of (A) Pt/ITO, (B) Pt/{PDDA-GN}/ITO, (C) Pt/{PDDA- GN/PSS-GN}/ITO, (D) Pt/{2PDDA-GN/PSS-GN}/ITO, (E) Pt/{2PDDA-GN/2PSS- GN}/ITO, and (F) Pt/ {3PDDA-GN/2PSS-GN}/ITO, at 0.2 V for 600 s.
in Fig. 4C and E. As compared to that on {n PDDA-GN/n 1 PSS-GN} (Fig. 4D), Pt nanoparticles on {n PDDA-GN/n PSS-GN} also aggregate to form micro–nanoclusters, but their dispersion is poorer. The linear negatively charged polyelectrolyte PSS in the PSS-GN also offers large and uniformly distributed active sites for anchoring metal ions and metal nanoparticles, but mutually exclusive interaction between 2 PtCl6 ions and PSS-GN may be responsible for the poorer dispersion of Pt micro–nanoclusters. In summary, it can be demonstrated that the {PDDA-GN/PSS-GN}n multilayer films play a special function in the formation of Pt micro–nanoclusters. As we all know, the process
of electrodeposition involves two parts, seed formation and growth [9]. Actually, the characters of deposited substrates would affect these two processes. For the Pt nanoparticles deposited onto bare ITO surface, the Pt seeds firstly appear and then grow into Pt nanoparticles. In such case, the growth process should dominate, and finally, nanoparticles could be formed [9]. On the other hand, for Pt nanoclusters deposited onto {PDDA-GN/PSS-GN}n multilayer films in our case, Pt seeds form on the surface at the primary stage but these seeds do not grow into larger Pt nanoparticles. After that, these small Pt nanoparticles aggregate to form Pt nanoclusters [38].
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Fig. 5. (A) CVs of Pt/{PDDA-GN/PSS-GN}n/GCE multilayer films with different layers; (B) CVs of Pt/{2PDDA/PSS}/GCE (1), Pt/GCE (2), and Pt/{2PDDA-GN/PSS-GN}/GCE (3). Scan rate 100 mV s 1, in 0.5 M H2SO4 + 1 M CH3OH.
The electrochemical oxidation of methanol was investigated by cyclic voltammetry in the solution containing 0.5 M H2SO4 + 1 M CH3OH (Fig. 5). Fig. 5A displays CV behavior of the Pt/{PDDA-GN/ PSS-GN}n/GCE films with different layers. It can be found that there are two anodic peaks in all CV curves. The forward anodic peak current at about 0.65 V is attributed to the electrooxidation of methanol, and the backward peak current at about 0.4 V originates from the removal of incompletely oxidized intermediate carbonaceous species formed in the forward scan on the surface of the catalysts, mainly CO [39]. The forward anodic peak current of Pt/ {PDDA-GN}/GCE (curve 5) is 1.4-fold higher than that of Pt/{PSSGN}/GCE (curve 1). And the Pt/{2PDDA-GN/PSS-GN}/GCE electrode shows the highest peak current and the greatest negative shift of the forward peak potential and backward peak potential, which is the evidence of highest electrocatalytic activity. As a whole, Pt supported on {n PDDA-GN/n 1 PSS-GN} (n = 1, 2, 3) with PDDAGN as the outmost layer exhibits higher electrocatalytic activity than that on {n PDDA-GN/n PSS-GN} (n = 1, 2). This may be attributed to the excellent binding capability between the positively charged PDDA and graphene [34]. Furthermore, during the electro2 deposition process, PtCl6 anions easily diffuse into the surface of PDDA-GN to form cauliflower like Pt micro–nanoclusters [37], which results in different electrochemical surface area (ECSA). Fig. S1 shows the CV curves of the Pt/{n PDDA-GN/m PSS-GN}/ GCE electrocatalysts in 0.5 M H2SO4 aqueous solutions. As illustrated by integrating the hydrogen adsorption/desorption charges according to the CV curves, the Pt/{2PDDA-GN/PSS-GN} films possess a relatively higher ECSA than that of Pt/{PDDA-GN/PSS-GN}, which helps enhance the catalytic activity. In order to make a comparison, the electrochemical oxidation of methanol of Pt particles electrodeposited on {2PDDA/PSS} and bare GCE were also investigated. As indicated in Fig. 5B, it is clearly seen that the highest forward anodic peak current of 1.5 mA is obtained as regards Pt/ {2PDDA-GN/PSS-GN}/GCE, which is about 1.5 times and 3.8 times as high as that of the Pt/GCE (0.97 mA), and Pt/{2PDDA/PSS}/GCE (0.39 mA), respectively. Moreover, the enhanced activity of Pt/ {2PDDA-GN/PSS-GN}/GCE was also evidenced by a lower onset potential. Apparently, this difference is mainly caused by the graphene-based multilayer films, which not only have superior electric conductivities, but also provide a novel catalyst support to improve the dispersion of Pt particles. To further evaluate the catalytic activity and stability of different films modified electrode in methanol oxidation, chronoampe-
rometry experiments were carried out in 0.5 M H2SO4 and 1.0 M CH3OH solutions under a constant potential of 0.65 V for 800 s. As shown in Fig. 6, the currents decrease quickly at the beginning, possibly owing to the formation of intermediate species and some poisonous species, such as COads and CHOads during the methanol oxidation reaction [40]. Afterward, the currents diminish much more slowly and reach a quasi-stationary within 800 s. This can be tentatively ascribed to the presence of surface active impurities or anions in the electrolyte solution that could slowly adsorb onto the electrode surface during long-term experiments, thereby determining the loss of activity [40]. The stability of the different films modified electrode follows the order of Pt/{2PDDA-GN/PSSGN}/GCE > Pt/{2PDDA/PSS} > Pt/GCE, which is consistent with the results obtained from the CV curves of methanol electrooxidation. In addition, it is evident that Pt/{2PDDA-GN/PSS-GN}/GCE shows lower decay of current with time and a obviously higher quasi-stationary current. These results strongly suggest that Pt/{2PDDA-GN/ PSS-GN}/GCE have a better tolerance toward CO poisoning than the others [4]. The enhanced catalytic activity and stability may be owing to the polymer-modified graphene (PDDA-GN and PSS-GN) preserves the superior electric conductivities in the multilayer films, which can be proven by Nyquist plots of the electrochemical impedance spectrum (EIS) (Fig. S2). Usually, the semicircle diameter is equal to the electron-transfer resistance (Rct), which is af-
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Time/s Fig. 6. Chronoamperometric curves of the different films modified electrode: (1) Pt/ GCE, (2) Pt/{2PDDA/PSS}/GCE, (3) Pt/{2PDDA-GN/PSS-GN}/GCE in 0.5 M H2SO4 + 1 M CH3OH at 0.65 V for 800 s.
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fected obviously by the surface modification of the electrode. As shown in Fig. S2, Rct decreases with the introduction of {2PDDAGN/PSS-GN} multilayer films. This means that polymer-modified graphene helps enhance electron transfer obviously on the electrode interface. 4. Conclusion In summary, graphene was functionally modified by PDDA and PSS. The {PDDA-GN/PSS-GN}n multilayer films were prepared by LBL method and used as a new kind of catalyst support for preparation of Pt nanoparticles through the electrodeposition in situ. Most interestingly, electrochemical investigation indicated that the presence of functionalized graphene in the Pt/{PDDA-GN/PSSGN}n modified electrodes greatly enhanced catalytic activity and stability toward methanol oxidation. The scalable chemical synthesis of graphene and the convenient preparation of multilayer films also provide a cost benefit of the electrocatalysts. The results demonstrate a promising approach for the development of low-cost and high-performance Pt-based anode electrocatalysts in fuel cells. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 21171037) and the Natural Science Foundation of Fujian Province (No. 2011J0101). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2012.10.058. References [1] X.L. Li, A. Faghri, C. Xu, Int. J. Hydrogen Energy 35 (2010) 8690. [2] Y.-H. Cho, H.-S. Park, Y.-H. Cho, I.-S. Park, Y.-E. Sung, Electrochim. Acta 53 (2008) 5909. [3] S.P. Jiang, Z. Liu, H.L. Tang, M. Pan, Electrochim. Acta 51 (2006) 5721. [4] J.R.C. Salgado, F. Alcaide, G. Álvarez, L. Calvillo, M.J. Lázaro, E. Pastor, J. Power Sources 195 (2010) 4022. [5] H. Zhu, Z. Guo, X. Zhang, K. Han, Y. Guo, F. Wang, Z. Wang, Y. Wei, Int. J. Hydrogen Energy 37 (2012) 873.
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[6] Y.Z. Zhang, Y.E. Gu, S.X. Lin, J.P. Wei, Z.H. Wang, C.M. Wang, Y.L. Du, W.C. Ye, Electrochim. Acta 56 (2011) 8746. [7] K. Fatih, V. Neburchilov, V. Alzate, R. Neagu, H. Wang, J. Power Sources 195 (2010) 7168. [8] H.J. Huang, H.Q. Chen, D.P. Sun, X. Wang, J. Power Sources 204 (2012) 46. [9] P. Wang, F. Li, X. Huang, Y. Li, L. Wang, Electrochem. Commun. 10 (2008) 195. [10] Y.C. Xin, J.G. Liu, Y. Zhou, W.M. Liu, J.A. Gao, Y. Xie, Y. Yin, Z.G. Zou, J. Power Sources 196 (2011) 1012. [11] S. Guo, S. Dong, Chem. Soc. Rev. 40 (2011) 2644. [12] X. Huang, Z. Yin, S. Wu, X. Qi, Q. He, Q. Zhang, Q. Yan, F. Boey, H. Zhang, Small 7 (2011) 1876. [13] T. Kuila, S. Bose, A.K. Mishra, P. Khanra, N.H. Kim, J.H. Lee, Polym. Test. 31 (2012) 31. [14] M. Dragoman, D. Dragoman, Prog. Quantum Electron. 33 (2009) 165. [15] Q.O. Zeng, J.S. Cheng, L.H. Tang, X.F. Liu, Y.Z. Liu, J.H. Li, J.H. Jiang, Adv. Funct. Mater. 20 (2010) 3366. [16] L. Grande, V.T. Chundi, D. Wei, C. Bower, P. Andrew, T. Ryhänen, Particuology 10 (2012) 1. [17] H. Gu, Y.Y. Yu, X.Q. Liu, B. Ni, T.S. Zhou, G.Y. Shi, Biosens. Bioelectron. 32 (2012) 118. [18] S. Kamada, H. Nomoto, K. Fukuda, T. Fukawa, H. Shirai, M. Kimura, Colloid. Polym. Sci. 289 (2011) 925. [19] Z. Spitalsky, M. Danko, J. Mosnacek, Curr. Org. Chem. 15 (2011) 1133. [20] J.M. Bak, T. Lee, E. Seo, Y. Lee, H.M. Jeong, B.S. Kim, H.I. Lee, Polymer 53 (2012) 316. [21] Y. Fu, S.-J. Li, J. Xu, M. Yang, J.-D. Zhang, Y.-H. Jiao, J.-C. Zhang, K. Zhang, Y.-G. Jia, Langmuir 27 (2010) 672. [22] Z.P. Li, J.Q. Wang, X.H. Liu, S. Liu, J.F. Ou, S.R. Yang, J. Mater. Chem. 21 (2011) 3397. [23] G. Decher, J.D. Hong, J. Schmitt, Thin Solid Films 210–211 (1992) 831. [24] A. Kazemi, J. Lahann, M. Madani, N. Sharifi-Sanjani, A. Hasan-Kaviar, Polym. Sci. Ser. B Polym. Chem. 52 (2010) 571. [25] Z.S. Li, S. Lin, Z.L. Chen, Y.D. Shi, X.M. Huang, J. Colloid Interface Sci. 368 (2012) 413. [26] Y. Lvov, G. Decher, H. Moehwald, Langmuir 9 (1993) 481. [27] A. Rani, K.A. Oh, H. Koo, H.J. Lee, M. Park, Appl. Surf. Sci. 257 (2011) 4982. [28] J. Yang, Y. Zhou, L. Sun, N. Zhao, C. Zang, X. Cheng, Appl. Surf. Sci. 258 (2012) 5056. [29] J. Shen, Y. Hu, C. Li, C. Qin, M. Shi, M. Ye, Langmuir 25 (2009) 6122. [30] W.S. Hummers, R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. [31] J.-J. Shi, G.-H. Yang, J.-J. Zhu, J. Mater. Chem. 21 (2011) 7343. [32] Q.W. Tang, J.H. Wu, Q.H. Li, J.M. Lin, Polymer 49 (2008) 5329. [33] S.Y. Wang, D.S. Yu, L.M. Dai, D.W. Chang, J.B. Baek, Acs Nano 5 (2011) 6202. [34] B.M. Luo, X.B. Yan, S. Xu, Q.J. Xue, Electrochim. Acta 59 (2012) 429. [35] S. Stankovich, R.D. Piner, X. Chen, N. Wu, S.T. Nguyen, R.S. Ruoff, J. Mater. Chem. 16 (2006) 155. [36] Z.Y. Sun, J.B. He, A. Kumbhar, J.Y. Fang, Langmuir 26 (2010) 4246. [37] L. Qian, X. Yang, Talanta 74 (2008) 1649. [38] L. Qian, X. Yang, J. Phys. Chem. B 110 (2006) 16672. [39] F. Ren, R. Zhou, F. Jiang, W. Zhou, Y. Du, J. Xu, C. Wang, Fuel Cells 12 (2012) 116. [40] J. Prabhuram, T.S. Zhao, Z.X. Liang, R. Chen, Electrochim. Acta 52 (2007) 2649.