J. Phys. Chem. C 2007, 111, 5715-5720
5715
Different Sized Platinum Nanoparticles Supported on Carbon: An XPS Study on These Methanol Oxidation Catalysts Fatih S¸ en†,‡ and Gu1 lsu1 n Go1 kagˇ ac¸ *,† Chemistry Department, Middle East Technical UniVersity, 06531 Ankara, Turkey ReceiVed: December 6, 2006; In Final Form: February 9, 2007
Different sized platinum nanoparticles on carbon supports have been prepared using PtCl4 (catalyst Ia) and H2PtCl6 (catalyst IIa) as starting materials and 1-hexanethiol as a surfactant and then heated to 200 °C (catalyst Ib and catalysts IIb), 300 °C (catalyst Ic and catalysts IIc), and 400 °C (catalyst Id and catalysts IId) for 4 h under argon gas. All the catalysts showed a face-centered cubic (fcc) crystal structure as determined by X-ray diffraction. X-ray diffractograms and transmission electron microscopy results reveal that the platinum nanoparticles are homogeneously dispersed on the carbon support, exhibit narrow particle size distribution, and show no appreciable aggregation. The average platinum particle size as determined from XRD data was found to be ∼2.00, ∼2.56, ∼4.23, ∼4.52, ∼2.13, ∼2.77, ∼4.29, and ∼4.62 nm for catalysts Ia-d and IIa-d, respectively. X-ray photoelectron spectra of all the catalysts indicated that most (>70%) of the platinum nanoparticles have an oxidation state of zero and a small amount (70%) with a smaller amount of an oxidized platinum species (70%) and the Pt 4f7/2 binding energy values positively shifted as temperature increased (going along the series catalysts Ia-d and catalysts IIa-d). This positive shift might be due to electron transfer from platinum nanoparticles to the carbon support during the heat treatment step. It is believed that the decrease in the electronic charge density on Pt(0) might cause a decline in the number of organic molecules adsorbed, which are needed for methanol oxidation reaction; this then causes a decrease in the performance of catalyst in the methanol oxidation reaction. Consequently, the activity of catalyst decreases as the temperature increases (catalysts Ia > Ib > Ic > Id and the same trend was observed for catalysts II). Acknowledgment. The authors gratefully acknowledge DPT (Devlet Planlama Tes¸ kilatı, Grant BAP-08-11-DPT2005K120590) and TU ¨ BI˙ TAK (Tu¨rkiye Bilimsel ve Teknik Aras¸ tırma Kurumu, Grant 104M266) for their financial support. The authors also would like to thank the Central Laboratory of the Middle East Technical University for XPS, ICP, and elemental analyses, Dr. Erdem Yas¸ ar (Kırıkkale U ¨ niversitesi) for TEM photographs, Dr. Metin Aydın for useful comments on FTIR data, and Dr. Michael W. Pitcher for the proofreading of this manuscript. F.S¸ . thanks Middle East Technical University for Grant BAP-0811-DPT2002K120510. References and Notes (1) Kardesch, K.; Simader, G. Fuel Cells and Their Applications; VCH: Weinheim, Germany, 1996.
S¸ en and Go¨kagˇac¸ (2) McNicol, B. D. J. Electoanal. Chem. 1981, 118, 71. (3) McNicol, B. D. D.; Dand, A. J.; Wiliams, K. R. J. Power Sources 1999, 83, 15. (4) Hearth, M. P. G.; Hards, A. Platinum Met. ReV. 1996, 40, 150. (5) Bagotsky, V. S.; Skundin, A. M. Chemical Power Sources; Academic Press: London, 1980. (6) Reddington, A.; Sapienza, B.; Gurau, R.; Viswanathan, S.; Sarangapani, E. S.; Smotkin, Mallouk, T. E. Science 1998, 280, 1735. (7) Arico, A. S.; Crinivasan, S.; Antonucci, V. Fuel Cells 2001, 2, 133. (8) Go¨kagˇac¸ , G.; Kennedy, B. J. Z. Naturforsch. 2002, 57b, 193. (9) Go¨kagˇac¸ , G. Metal Oxides as Promoters for Methanol Oxidation. Ph.D.Thesis, University of Sydney, Sydney, Australia, 1994. (10) Arico, A. S.; Shukla, A. K.; El-Khatib, K. M.; Creti, P.; Antonucci, V. J. Appl. Electrochem. 1999, 29, 671. (11) Li, X.; Chen, W-X.; Zhao, J.; Xing, W.; Xu, Z-D. Carbon 2005, 2168. (12) Guo, D-J.; Li, H-L. J. Electroanal. Chem. 2004, 573, 197. (13) Tian, Z. Q.; Jiang, S. P.; Liang, Y. M.; Sten, P. K. J. Phys. Chem. B 2006, 110, 5350. (14) Go¨kagˇac¸ , G.; Leger, J. M.; Hahn, F. Z. Naturforsch. 2003, 58b, 423. (15) Klug, H.; Alexander, L. X ray Diffraction Procedures; Wiley: New York, 1962. (16) Kawaguchi, T.; Sugimoto, W.; Murakami, Y.; Takasu, Y. J. Catal. 2005, 229, 176. (17) Yang, R.; Qiu, X.; Zhang, H.; Li, J.; Zhu, W.; Wang, Z.; Huang, X.; Chen, L. Carbon 2005, 11. (18) (a) Liu, Z.; Ling, X. Y.; Lee, J. Y.; Su, X.; Gan, L. M. J. Mater. Chem. 2003, 13, 3049. (b) C¸ elik, A. M. S. Thesis, Middle East Technical University, Ankara, Turkey, 2004. (19) Kuo, P.-L.; Chen, W.-F.; Hhang, H. Y.; Chang, I.-C.; Dia, S. A. J. Phys. Chem. B 2006, 110, 3071. (20) (a) Hastetler, M. J.; Stokes, J. J.; Murray, R. W. Langmuir 1996, 12, 3604. (b) S¸ en, F.; Go¨kagˇac¸ , G. J. Phys. Chem. C 2007, 111, 1467. (21) Biegler, T. Aust. J. Chem. 1973, 26, 2571. (22) Hampson, N. A.; Willars, M. J. J. Power Sources 1979, 4, 191. (23) Babu, P. K.; Kim, H. S.; Kuk, S. T.; Chung, J. H.; Oldfield, E.; Wieckowski, A.; Smotkin, E. S. J. Phys. Chem. B 2005, 109, 17192. (24) Liu, Z.; Ling, X. Y.; Su, X.; Lee, J. Y. J. Phys. Chem. B 2004, 108, 8234. (25) Goodenough, J. B.; Hamnett, A.; Kennedy, B. J.; Manoharan, R.; Weeks, S. A. J. Electroanal. Chem. 1988, 240, 133. (26) Watanabe, W.; Uchida, M.; Motoo, S. J. Electroanal. Chem. 1987, 229, 395. (27) Allen, G. C.; Tucker, P. M.; Capon, A.; Parsons, R. J. Electroanal. Chem. 1974, 50, 335. (28) Kim, K. S.; Winograd, N.; Davis, R. E. J. Am. Chem. Soc. 1971, 93, 6296. (29) Szymanski, R.; Charcosset, J. Mol. Catal. 1984, 25, 337. (30) Goodenough, J. B.; Hamnett, A.; Kennedy, B. J.; Weeks, S. A. Electrochem. Acta 1987, 32, 1233. (31) Gasteiger, H. A.; Markovic, N.; Ross, P. N.; Cairns, E. J. J. Phys. Chem. 1993, 97, 12020. (32) Ticarelli, E.; Beery, J. G.; Paffet, M. T.; Gottesfeld, S. J. J. Electroanal. Chem. 1989, 258. (33) Gasteiger, H. A.; Marcovic, N.; Ross, P. N., Jr.; Cairns, E. J. J. Electrochem. Soc. 1994, 141, 1795. (34) Anderson, A. B.; Grantscharova, E. J. Phys. Chem. 1995, 99, 9149. (35) Hamnett, A. Catal. Today 1997, 38, 445.
