DOI: 10.1002/chem.201302579

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& Electrochemistry

Synthesis of Mesoporous Platinum–Copper Films by Electrochemical Micelle Assembly and Their Electrochemical Applications Cuiling Li[a] and Yusuke Yamauchi*[a, b, c]

Abstract: We have electrochemically synthesized mesoporous platinum–copper films with various compositions in an aqueous surfactant solution. By tuning the composition ratios of the platinum and copper sources in the precursor solutions, mesoporous bimetallic films with copper contents that dramatically change from 0 to 70 mol % can be successfully prepared. The obtained bimetallic films possess uni-

formly sized mesopores over the entire area. These mesoporous platinum–copper films are electrochemically active and show composition-dependent catalytic activity and stability for the methanol oxidation reaction. The bimetallic mesoporous films are a promising new class of electrocatalyst for the future.

Introduction

of platinum. The platinum–copper bimetallic materials exhibit remarkably improved electrocatalytic activity in the MOR.[17–19] For further enhancement in the overall electrocatalytic activity and higher utilization efficiency of platinum, precisely designing the platinum–copper bimetallic nanostructures is important. Previous reports have demonstrated that well-defined meso-/nanoporous materials exhibited superior electrochemical properties because of their high porosity, large area per unit volume, and excellent structure–activity relationship.[20–23] The aim of this work was to fabricate mesoporous-structured metals that could be used directly in on-chip DMFCs. Among variously shaped mesoporous metals, continuous mesoporous films show more advantageous potential usage in on-chip power sources because they can be directly utilized as electrode materials. Many efforts have been made in the design and synthesis of mesoporous metal films and several methods have been developed so far, including electrochemical micelle assembly,[24–26] lyotropic liquid-crystal templating,[22, 27–29] dealloying process,[30–32] and block copolymer templating.[33] Recently, we established a new synthetic concept of “electrochemical micelle assembly” for the fabrication of ordered mesoporous platinum by simple electrochemical plating in aqueous surfactant solutions.[24, 26] This electrochemical micelle assembly has sparked much attention. The electrochemical deposition technique is more convenient in the preparation of electrodes, which can be used directly in miniature devices. Therefore, our method is more feasible, versatile, and advantageous than other methods. In this work, we extend our concept of electrochemical micelle assembly to other kinds of mesoporous platinum-based systems, especially those mesoporous platinum-based alloys films with cheaper metals but more effective electrocatalytic performance. Herein, we successfully synthesized mesoporous platinum–copper films by using the electrochemical micelle as-

The rapid development of miniature devices has resulted in continuously growing research interest on novel structured materials for minimizing power sources.[1–5] Direct methanol fuel cells (DMFCs), which have been widely studied in practical applications because of their important roles in converting chemical energy into electrical energy, is a superior candidate for miniature power sources.[6–8] The outstanding electrochemical activity of platinum for the methanol oxidation reaction (MOR, for the anodic reaction of DMFCs) and the serious poisoning effect caused by CO intermediates have been proved in recent decades. Introducing a second metal into Pt is a common approach to facilitate the removal of CO or to inhibit the formation of CO on the Pt surface by a bifunctional mechanism or electronic effects.[9–14] For example, Pt Au alloys show gradual inhibition of the formation of CO with increasing Au content[15] and yolk–shell-structured Au Pt also shows excellent CO-tolerance stability.[16] Recently, the incorporation of copper into platinum-based catalysts has attracted much attention to further enhance overall electrocatalytic performance [a] Dr. C. Li, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan) E-mail: [email protected] [b] Prof. Dr. Y. Yamauchi Department of Nanoscience and Nanoengineering Faculty of Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan) [c] Prof. Dr. Y. Yamauchi Precursory Research for Embryonic Science and Technology (PRESTO) (Japan) Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan) Chem. Eur. J. 2014, 20, 729 – 733

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Full Paper sembly of nonionic surfactants (Brij 58). These mesoporous platinum–copper films were electrochemically active and showed composition-dependent catalytic activity and stability for the MOR. The synthesis of mesoporous films prepared by means of micelle assembly is desirable for the fabrication of on-chip power sources. The bimetallic mesoporous films are a promising new class of electrocatalyst for use in the future.

Results and Discussion Mesoporous Pt Cu films were electrochemically deposited on conductive Au-coated Si substrate by applying a constant reducing potential of 0.2 V in the electrolyte consisting 10 mm metal precursor and 1.0 wt % Brij 58 (C16H33(OCH2CH2)20OH). Inductively coupled plasma mass spectroscopy (ICP-MS) was used to characterize the exact composition of the as-prepared mesoporous films. The content of both platinum and copper in the products was linearly varied by changing the content of their corresponding metallic precursors in the starting electrolyte solutions (Figure 1). Hereafter, PtxCu100 x (x means the molar percentage of Pt) films were used as abbreviations for the films prepared from different precursor solutions. By precisely controlling the compositional ratios (Pt and Cu sources)

Figure 2. Top-surface SEM images of Pt Cu films with different compositional ratios: a) Pt, b) Pt86Cu14, c) Pt73Cu27, d) Pt57Cu43, e) Pt39Cu61, and f) Pt30Cu70, prepared from precursor solutions of [PtCl4]2 /Cu2 + = 100:0, 90:10, 80:20, 65:35, 50:50, and 40:60, respectively.

showed a difference when the precursor compositions were varied. With increasing Cu content, the surface structures of the Pt Cu films changed from flat to cauliflower-like surfaces and then back again to flat surfaces. Serious cracks and voids could not be observed in any of the films. The mesostructural periodicity of all films was further investigated by low-angle XRD measurements (Figure 3 a). One broad peak was clearly

Figure 1. Relationship between the product and precursor compositions.

Figure 3. a) Low- and b) wide-angle XRD patterns of Pt Cu films with different compositional ratios (Pt, Pt86Cu14, Pt73Cu27, Pt57Cu43, Pt39Cu61, and Pt30Cu70, prepared from the precursor solutions of [PtCl4]2 /Cu2 + = 100:0, 90:10, 80:20, 65:35, 50:50, and 40:60, respectively).

in the electrolyte solutions, Pt Cu films with various molar ratios were successfully obtained. The compositional ratios of the obtained mesoporous films were Pt (from [PtCl4]2 /Cu2 + = 100:0), Pt86Cu14 (from [PtCl4]2 /Cu2 + = 90:10), Pt73Cu27 (from [PtCl4]2 /Cu2 + = 80:20), Pt57Cu43 (from [PtCl4]2 /Cu2 + = 65:35), Pt39Cu61 (from [PtCl4]2 /Cu2 + = 50:50), and Pt30Cu70 (from [PtCl4]2 /Cu2 + = 40:60). As clearly seen in Figure 1, the deposition of copper was easier than that of platinum, when the electrostatic potential was applied between the working and reference electrodes, because the standard redox potential of [PtCl4]2 /Pt (0.76 V vs. a standard calomel electrode (SCE)) was higher than that of Cu2 + /Cu (0.34 V vs. SCE). Figure 2 shows top-surface SEM images of the obtained Pt Cu films prepared from various precursor compositions. Highly dispersed mesopores with uniform sizes could be clearly confirmed in each film. The surface structure of the Pt Cu films Chem. Eur. J. 2014, 20, 729 – 733

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observed for each film; this indicated the formation of wellorganized mesoporous films, even when the copper content was dramatically changed from 0 to 70 % (Figure 3 a). The peak positions shifted to a higher angle range when the copper content increased from 0 to 27 mol %, and remained almost constant after that. The crystalline structures and electric states of platinum and copper in the films were investigated by wide-angle XRD and X-ray photoelectronic spectroscopy (XPS). The wide-angle XRD patterns of mesoporous Pt Cu films and mesoporous Pt film shows similar profiles that can be assigned to a face-centered cubic (fcc) crystal structure. The peak positions in the high730

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Full Paper angle range, such as the (311) peak, significantly shifted with increasing Cu content in the mesoporous Pt Cu films, due to differences in the lattice spacing between the Pt and Cu fcc structures (Figure 3 b).[34] The peaks became sharper, which indicated enlargement of the crystalline sizes (Figure 3 b). The XPS spectra of the Pt 4f and Cu 2p regions for mesoporous Pt Cu films were carefully measured (not shown). The peaks at binding energies of 74.5 and 71.0 eV fitted the Pt0 4f5/2 and Pt0 4f7/2 peaks well, whereas peaks at binding energies of 952.5 and 932.4 eV were in good agreement with the Cu0 2p1/2 and Cu0 2p3/2 peaks.[35–39] The peaks of Pt0 and Cu0 and the absence of other valences confirmed the good reduction of [PtCl4]2 and Cu2 + to the metallic state by using the applied negative potential. The cross-sectional morphology of the mesoporous Pt86Cu14 film (prepared from [PtCl4]2 /Cu2 + = 90:10) was carefully characterized by SEM, as shown in Figure 4. SEM analysis revealed a well-organized mesoporous structure with uniform pore sizes distributed all over the film, from the surface to the inner part. The thickness of the highly porous film reached around 550 nm after electrodeposition for 10 min. The growth rate was around 0.9 nm s 1. The observed pore sizes were measured to be 7–8 nm, which coincided with the calculated mesopore size replicated from Brij 58 micelles.[24, 26] The dissolved aqua–platinum species coordinated by water molecules can be incorporated into the outer part of hydrophilic shell in spherical micelles.[24, 26] Similarly, the dissolved aqua–copper species are also thought to be adsorbed in the range of the ethylene oxide (EO) region. During electrochemical deposition, the metal species approach the working electrode with surfactant micelles. Therefore, the micelles can serve as direct template for the pores. Figure 5 shows TEM images of mesoporous

Figure 5. TEM study of the mesoporous Pt86Cu14 film prepared from a precursor solution with [PtCl4]2 /Cu2 + = 90:10. a) A bright-field TEM image and selected-area electron diffraction (SAED) pattern, b) a high-resolution TEM image of the film edge, c) a high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image, and corresponding elemental mapping images: d) Pt and e) Cu.

Pt86Cu14 film. The SAED patterns showed the diffused ring patterns characteristic of a fcc structure. It is evident from Figure 5 b that the lattice fringes go throughout the pore walls. The HAADF-STEM image displayed in Figure 5 c shows the highly porous structure all over the films. From the nanoscale mapping of Pt and Cu elements, Pt and Cu were evenly dispersed all over the films (Figure 5 d and e). The molar ratio between Pt and Cu was 85:15, which was in accordance with the ICP-MS result. The mesoporous Pt57Cu43 film (from [PtCl4]2 /Cu2 + = 65:35) was also characterized by SEM and TEM (Figure 6). The mesoporous layer was uniformly deposited on the substrate surface without any cracks and voids. After electrodeposition at 0.2 V for 600 s, the thickness of mesoporous Pt57Cu43 reached 550 nm, which was almost the same as that of the mesoporous Pt86Cu14 film. From the corresponding elemental mapping results, platinum and copper were uniformly distributed over the

Figure 6. SEM images (a and b) at different magnifications; b) is an enlargement of the area within the square in a). HAADF-STEM image (c) and corresponding elemental mapping images (Pt (d) and Cu (e)) of the mesoporous Pt57Cu43 film prepared from a precursor solution with [PtCl4]2 /Cu2 + = 65:35.

Figure 4. Top surface (a and b) and cross-sectional (c and d) SEM images of mesoporous Pt86Cu14 film prepared from a precursor solution with [PtCl4]2 / Cu2 + = 90:10. Chem. Eur. J. 2014, 20, 729 – 733

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Full Paper entire area without any phase segregation on a nanometer scale. Mesoporous Pt Cu films were evaluated by their electrocatalytic activity toward the MOR. After careful removal of surfactants, the mesoporous Pt Cu films were directly used as the working electrodes. All of the electrocatalytic experiments were performed in a 0.5 m solution of H2SO4 containing 500 mm of CH3OH at a scan rate of 50 mV s 1 at room temperature. Cyclic voltammograms of the mesoporous Pt57Cu43 film, the mesoporous Pt86Cu14 film, and the mesoporous Pt film were measured. Two visible anodic peaks, occurring on the positive and negative sweeps, were observed; this was a typical feature of the MOR on a Pt surface (not shown). Figure 7 a summarizes linear sweep voltammograms (LSVs) of the mesoporous Pt57Cu43 film, the mesoporous Pt86Cu14 film, and the mesoporous Pt film. In Figure 7, all the currents were normalized by the Pt ECSAs of each film electrode. The Pt ECSAs were estimated by integrating the charge passed during hydrogen adsorption/desorption on the electrode surface by assuming that the charge required to oxidize a monolayer of hydrogen on Pt surface was 210 mC cm 2. The mesoporous Pt57Cu43 film showed the highest activity by displaying the least-positive oxidation peak potential of

Table 1. Onset potentials, forward (If), backward (Ib) peak current densities, and the If/Ib ratios for mesoporous Pt Cu films with different compositions.

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Onset potential [V]

If [mA cm 2]

Ib [mA cm 2]

If/Ib

Pt Pt86Cu14 Pt57Cu43 Pt39Cu61 Pt30Cu70

0.22 0.21 0.18 0.16 0.15

0.96 0.98 1.02 0.80 0.55

1.37 1.26 0.98 0.72 0.43

0.70 0.77 1.04 1.11 1.28

0.70 V and a high mass current density of 1.02 mA cm 2 Pt. The specific current density of mesoporous Pt57Cu43 at the peak potential was 1.04 and 1.06 times higher than those of the mesoporous Pt86Cu14 film (0.98 mA cm 2 Pt) and the mesoporous Pt film (0.96 mA cm 2 Pt), respectively. The higher current density of the mesoporous Pt57Cu43 film than that of mesoporous Pt films verified the higher utilization efficiency of Pt. The most important point is that the onset potential and peak potential of the mesoporous Pt Cu films negatively shifted relative to that of the mesoporous Pt film (Figure 7 a, inset). Similar phenomena could be observed for other mesoporous Pt Cu films with a high Cu content, although their current densities gradually decreased (Table 1). The value of If/Ib (defined as the ratio between the forward and backward current densities) can be used as an indicator of the CO tolerance of Pt catalysts in the MOR. The If/Ib values were 1.04, 0.77, and 0.70 for mesoporous Pt57Cu43, Pt86Cu14, and Pt film, respectively. The higher If/Ib value of the mesoporous Pt57Cu43 film indicates its relatively good CO tolerance.[40] Increasing the copper content further to 61 and 70 %, resulted in a further increase of the If/Ib ratio to 1.11 and 1.28, respectively. The highly improved activity and CO-tolerant performance of the mesoporous Pt Cu films are due to the incorporation of Cu into the Pt systems. The Cu surface sites can allow the facile formation of oxygenated species to oxidize the dissociative intermediates produced on nearby Pt sites to facilitate the elimination of the poisonous effect of CO on Pt surfaces.[41] However, as an effective component toward the MOR, the active Pt surfaces are highly desired for the activity of the catalysts. The balance between active Pt sites and the CO-tolerant Cu site is important for the MOR. This is the reason that mesoporous Pt57Cu43 exhibited a higher current density than those of mesoporous films with other components. However, the incorporation of copper into the mesoporous films resulted in poorer long-term stability than that of the pure platinum film (Figure 7 b). This may be caused by the less stable property of copper; a similar situation was reported previously.[42] A study on improving the stability of mesoporous Pt Cu films is still underway.

Figure 7. a) LSVs and b) chronoamperograms for mesoporous Pt, Pt86Cu14, and Pt57Cu43 films in a 0.5 m solution of H2SO4 containing 500 mm of methanol. The LSVs were recorded from 0.0 to 1.0 V (vs. Ag/AgCl) at a scan rate of 50 mV s 1, whereas the chronoamperograms were recorded at a constant potential of 0.6 V (vs. Ag/AgCl). All films were the same thickness of about 550 nm. All currents were normalized by the platinum electrochemical surface areas (Pt ECSAs). Chem. Eur. J. 2014, 20, 729 – 733

Pt Cu films

Conclusion Mesoporous Pt Cu films with various compositions were successfully prepared by a facile electrochemical method in an aqueous surfactant solution containing the corresponding metal precursors with various ratios. Due to the synergistic 732

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Full Paper effect of mesoporous structures and Pt Cu binary surfaces, the obtained mesoporous Pt Cu films showed superior catalytic activity towards methanol oxidation. Mesoporous Pt Cu films showed composition-dependent MOR activity and stability, and the mesoporous Pt57Cu43 film was the most efficient MOR catalyst with a current density reaching 1.02 mA cm 2 Pt and a negatively shifted onset potential. The reported mesoporous Pt Cu films should offer a new avenue for the fabrication of mesoporous electrodes in on-chip fuel cells and other small devices.

[5] S. Tominaka, M. Shigeto, H. Nishizeko, T. Osaka, Chem. Commun. 2010, 46, 8989. [6] Y. Bing, H. Liu, L. Zhang, D. Ghosh, J. Zhang, Chem. Soc. Rev. 2010, 39, 2184. [7] T. Maiyalagan, X. Dong, P. Chen, X. Wang, J. Mater. Chem. 2012, 22, 5286. [8] S. Wang, S. P. Jiang, X. Wang, J. Guo, Electrochim. Acta 2011, 56, 1563. [9] L. Wang, Y. Nemoto, Y. Yamauchi, J. Am. Chem. Soc. 2011, 133, 9674. [10] S. Guo, S. Dong, E. Wang, ACS Nano 2010, 4, 547. [11] X. Zhao, M. Yin, L. Ma, L. Liang, C. Liu, J. Liao, T. Lu, W. Xing, Energy Environ. Sci. 2011, 4, 2736. [12] X. Bo, L. Zhu, G. Wang, L. Guo, J. Mater. Chem. 2012, 22, 5758. [13] F. Bai, Z. Sun, H. Wu, R. E. Haddad, X. Xiao, H. Fan, Nano Lett. 2011, 11, 3759. [14] M. Cao, D. Wu, S. Gao, R. Cao, Chem. Eur. J. 2012, 18, 12978. [15] M. Yin, Y. Huang, L. Liang, J. Liao, C. Liu, W. Xing, Chem. Commun. 2011, 47, 8172. [16] L. Kuai, S. Wang, B. Geng, Chem. Commun. 2011, 47, 6093. [17] D. Xu, Z. Liu, H. Yang, Q. Liu, J. Zhang, J. Fang, S. Zou, K. Sun, Angew. Chem. 2009, 121, 4281; Angew. Chem. Int. Ed. 2009, 48, 4217. [18] X. Liu, W. Wang, H. Li, L. Li, G. Zhou, R. Yu, D. Wang, Y. Li, Sci. Rep. 2013, 3, 1. [19] X. Huang, Y. Li, Y. Chen, E. Zhou, Y. Xu, H. Zhou, X. Duan, Y. Huang, Angew. Chem. 2013, 125, 2580; Angew. Chem. Int. Ed. 2013, 52, 2520. [20] G. S. Attard, C. G. Gçltner, J. M. Corker, S. Henke, R. H. Templer, Angew. Chem. 1997, 109, 1372; Angew. Chem. Int. Ed. Engl. 1997, 36, 1315. [21] H. Ataee-Esfahani, J. Liu, M. Hu, N. Miyamoto, S. Tominaka, K. C. W. Wu, Y. Yamauchi, Small 2013, 9, 1047. [22] G. S. Attard, P. N. Bartlett, N. R. B. Coleman, J. M. Elliott, J. R. Owen, J. H. Wang, Science 1997, 278, 838. [23] K. S. Choi, E. W. McFarland, G. D. Stucky, Adv. Mater. 2003, 15, 2018. [24] H. Wang, L. Wang, T. Sato, Y. Sakamoto, S. Tominaka, K. Miyasaka, N. Miyamoto, Y. Nemoto, O. Terasaki, Y. Yamauchi, Chem. Mater. 2012, 24, 1591. [25] C. Li, H. Wang, Y. Yamauchi, Chem. Eur. J. 2013, 19, 2242. [26] C. Li, T. Sato, Y. Yamauchi, Angew. Chem. 2013, 125, 8208; Angew. Chem. Int. Ed. 2013, 52, 8050. [27] Y. Yamauchi, M. Komatsu, M. Fuziwara, Y. Nemoto, K. Sato, T. Yokoshima, H. Sukegawa, K. Inomata, K. Kuroda, Angew. Chem. 2009, 121, 7932; Angew. Chem. Int. Ed. 2009, 48, 7792. [28] Y. Yamauchi, A. Sugiyama, R. Morimoto, A. Takai, K. Kuroda, Angew. Chem. 2008, 120, 5451; Angew. Chem. Int. Ed. 2008, 47, 5371. [29] Y. Yamauchi, A. Takai, T. Nagaura, S. Inoue, K. Kuroda, J. Am. Chem. Soc. 2008, 130, 5426. [30] J. Erlebacher, M. J. Azlz, A. Karma, N. Dimitrov, K. Sieradzki, Nature 2001, 410, 450. [31] A. Wittstock, V. Zielasek, J. Biener, C. M. Friend, M. Bumer, Science 2010, 327, 319. [32] H. Qiu, F. Zou, ACS Appl. Mater. Interfaces 2012, 4, 1404. [33] S. C. Warren, L. C. Messina, L. S. Slaughter, M. Kamperman, Q. Zhou, S. M. Gruner, F. J. DiSalvo, U. Wiesner, Science 2008, 320, 1748. [34] C. Joyce, L. Trahey, S. A. Bauer, F. Dogan, J. T. Vaughey, J. Electrochem. Soc. 2012, 159, A909. [35] Y. Chen, Z. Liang, F. Yang, Y. Liu, S. Chen, J. Phys. Chem. C 2011, 115, 24073. [36] M.-F. Luo, C.-C. Wang, G.-R. Hu, W.-R. Lin, C.-Y. Ho, Y.-C. Lin, Y.-J. Hsu, J. Phys. Chem. C 2009, 113, 21054. [37] J. Zeng, J. Yang, J. Y. Lee, W. Zhou, J. Phys. Chem. B 2006, 110, 24606. [38] J. Fan, Y. Dai, Y. Li, N. Zheng, J. Guo, X. Yan, G. D. Stucky, J. Am. Chem. Soc. 2009, 131, 15568. [39] a) G. Liu, T. P. St. Clair, D. W. Goodman, J. Phys. Chem. B 1999, 103, 8578; b) W. Xiao, K. Xie, Q. Guo, E. G. Wang, J. Phys. Chem. B 2002, 106, 4721. [40] C. Li, Y. Yamauchi, Phys. Chem. Chem. Phys. 2013, 15, 3490. [41] Z. Yin, W. Zhou, Y. Gao, D. Ma, C. J. Kiely, X. Bao, Chem. Eur. J. 2012, 18, 4887. [42] S. Guo, S. Zhang, X. Sun, S. Sun, J. Am. Chem. Soc. 2011, 133, 15354.

Experimental Section Preparation of mesoporous Pt Cu films A typical synthesis of mesoporous Pt Cu films was carried out at a constant potential of 0.2 V by using an electrochemical machine (CHI 842B electrochemical analyzer, CH Instrument, U.S.) with a standard three-electrode cell system, including an Ag/AgCl (saturated KCl) electrode as a reference electrode, a platinum wire as a counter electrode, and Au Si substrate as a working electrode. The electrolyte solution used contained K2PtCl4 and CuCl2 with Brij 58 (C16H33(OCH2CH2)20OH, 1.0 wt %) as the surfactant. K2PtCl4 and CuCl2·2 H2O were used as the metal sources. The total concentration of metal precursors was 10 mm. The molar ratios of Pt to Cu species were gradually changed ([PtCl4]2 /Cu2 + = 100:0, 90:10, 80:20, 65:45, 50:50, and 40:60, respectively) for the preparation of mesoporous Pt Cu films with different compositions. After electrodeposition for 600 s, as-prepared films were soaked in ethanol for 24 h to extract the surfactants, then thoroughly rinsed with de-ionized water, and dried in air.

Characterization SEM images were obtained by using a Hitachi HR-SEM SU8000 microscope. The accelerating voltage was 5 kV. TEM images were obtained by using a JEOL JEM-2100F microscope with an accelerating voltage of 200 kV. Powder samples scratched from the substrates were dispersed in ethanol and mounted on a microgrid. Low-angle XRD patterns were recorded by using a Rigaku NANO-Viewer (CuKa radiation) instrument with a camera length of 700 mm operated at 40 kV and 30 mA. Wide-angle XRD spectra were recorded with a Rigaku Rint 2500 diffractometer with monochromated CuKa radiation operated by using a step-scan program. XPS results were recorded at room temperature by using a JPS-9010TR (JEOL) instrument with a MgKa X-ray source. Cyclic voltammetry and amperometry measurements were performed by using a CHI 842B electrochemical analyzer (CH Instruments). A conventional three-electrode cell was used, including an Ag/AgCl electrode as the reference electrode, a platinum wire as the counter electrode, and a working electrode.

Keywords: copper · electrochemistry · mesoporous materials · methanol oxidation reaction · platinum [1] S. Tominaka, S. Ohta, H. Obata, T. Momma, T. Osaka, J. Am. Chem. Soc. 2008, 130, 10456. [2] W. Wu, S. Bai, M. Yuan, Y. Qin, Z. L. Wang, T. Jing, ACS Nano 2012, 6, 6231. [3] L. Baraban, D. Makarov, R. Streubel, I. Mçnch, D. Grimm, S. Sanchez, O. G. Schmidt, ACS Nano 2012, 6, 3383. [4] M. Zhou, N. Zhou, F. Kuralay, J. R. Windmiller, S. Parkhomovsky, G. Valds-Ramrez, E. Katz, J. Wang, Angew. Chem. 2012, 124, 2740; Angew. Chem. Int. Ed. 2012, 51, 2686.

Chem. Eur. J. 2014, 20, 729 – 733

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Received: July 3, 2013 Published online on December 12, 2013

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Synthesis of mesoporous platinum-copper films by electrochemical micelle assembly and their electrochemical applications.

We have electrochemically synthesized mesoporous platinum-copper films with various compositions in an aqueous surfactant solution. By tuning the comp...
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