The studies described in this paper indicate that XAS based methodology is promising to elucidate the formation mechanism of bimetallic NPs. The XAS results demonstrate that the reduction of platinum hydroxide and ruthenium oxide species under flowing hydrogen resulted in metallic Pt–Ru nanoparticles.
XAS results of the present study reveals that the mixing of Pt4+ ions with a ligand environment of OH– groups and Ru4+ ions surrounded by oxygen groups at 100 0C for 8 hrs prior to H2 reduction initiates the reduction reaction as evidenced by the presence of Pt and Ru bimetallic and ionic contribution and is
24 beneficial to enhance the atomic distribution and is suitable for the formation of well-dispersed Pt–Ru/C nanoparticles. Even though our XAS results reasonably suggest the presence of both Pt and Ru metallic and ionic contributions in the colloidal product the exact mechanism of this step needs further studies and we will address this in our future contributions. The carbon-supported Pt–Ru nanoparticles thus obtained have structure similar to Pt-rich core and Ru-rich shell. Based on the XAS structural parameters we found that atomic-scale distribution of Ru is much better than Pt. The proposed methodology is quite general and easy to extend to study the formation mechanism of other metallic clusters.
Acknowledgement.
The financial support from the National Science Council (under contract numbers NSC93-2811-E-011-008, NSC94-2214-E-011-010, and NSC94-2120-M-011-002), facilities from the National Synchrotron Radiation Research Center (NSRRC), and the National Taiwan University of Science and Technology, Taiwan, R. O. C is gratefully acknowledged.References
1. Hogarth, M. P.; Hards, G. A. Platinum Metals Rev. 1996, 40, 150.
2. Watanabe, M.; Motto, S. J. Electroanal. Chem. 1975, 60, 267.
3. (a) Lu, C.; Rice, C.; Masel, M. I.; Babu, P. K.; Waszczuk, P.; Kim, H. S.; Oldfield, E.;
Wieckowski, A. J. Phys. Chem. B 2002, 106, 9581. (b) Waszczuk, P.; Lu, G. U.; Wieckowski, A.;
Lu, C.; Rice, C.; Masel, M. I. Electrochim. Acta 2002, 47, 36.
4. Waszczuk, P.; Wieckowski, A.; Zelenay, P.; Gottesfeld, S.; Coutanceau, C.; Léger, J.-M.; Lamy, C. J. Electroanal. Chem. 2001, 511, 55.
5. (a) Schmidt, T. J.; Noeske, M.; Gasteiger, H. A.; Behm, R. J.; Britz, P.; Brijouz, W.; Bönnemann, H. Langmuir 1997, 13, 2591. (b) Vogel, W.; Britz, P.; Bönnemann, H.; Rothe, J. J. Phys. Chem.
B 1997, 101, 11029. (c) Bönnemann, H.; Brinkmann, R.; Britz, P.; Endruschat, U.; Mortel, R.;
Paulus, U. A.; Feldmeyer, G. J.; Schmidt, T. J. J. New Mater. Electrochem. Syst. 2000, 3, 199.
25 6. (a) Zhang, X.; Chan, K.-Y. Chem. Mater. 2003, 15, 451. (b) Liu, Y.; Qiu, X.; Chen, Z.; Zhu, W.
Electrochem. Commun. 2002, 4, 550.
7. Boxall, D. L.; Deluga, G. A.; Kenik, E. A.; King, W. D.; Lukehart, C. M. Chem. Mater. 2001, 13, 891.
8. (a) Wang, X.; Hsing, I.-M. Electrochim. Acta 2002, 47, 2981. (b) Sarma, L. S.; Lin, T.-D.; Tsai, Y.-W.; Chen, J.-M.; Hwang, B.-J. J. Power Sources 2005, 139, 44.
9. (a) Nashner, M. S.; Frenkel, A. I.; Somerville, D.; Hills, C. W.; Shapley, J. R.; Nuzzo, R. G. J.
Am. Chem. Soc. 1998, 120, 8093. (b) Nashner, M. S.; Frenkel, A. I.; Adler, D. L.; Shapley, J. R.;
Nuzzo, R. G. J. Am. Chem. Soc. 1997, 119, 7760.
10. Watanabe, M.; Uchida, M.; Motoo, S. J. Electroanal. Chem. 1987, 229, 395.
11. (a) Tsai, Y.-W.; Tseng, Y.-L.; Sarma, L. S.; Liu, D.-G.; Lee, J.-F.; Hwang, B.-J. J. Phys. Chem.
B 2004, 108, 8148. (b) Hwang, B.-J.; Tsai, Y.-W.; Sarma, L. S.; Liu, D.-G.; Lee, J.-F. J. Phys.
Chem. B 2004, 108, 20427. (c) Chen, C.-H.; Hwang, B.-J.; Wang, G.-R.; Sarma, L. S.; Tang, M.-T.; Liu, D.-G.; Lee, J.-F. J. Phys. Chem. B 2005, 109, 21566.
12. Frenkel, A. I.; Hill, C. W.; Nuzzo, R. G. J. Phys. Chem. B 2001, 105, 12689.
13. B.-J. Hwang, L. S. Sarma, M. Chen, C.-H. Chen, S.-C. Shih, G.-R. Wang, Liu, D.-G.; Lee, J.-F.; Tang, M.-T. J. Am. Chem. Soc. 2005, 127, 11140.
14. Bock, C.; Paquet, C.; Couillard, M.; Botton, G. A.; MacDougall, B. R. J. Am. Chem. Soc. 2004, 126, 8028.
15. (a) Zhang, Z. C.; Lei, G. D.; Sachtler, W. M. H. In Series on Synchrotron Radiation Techniques and Applications; Iwasawa, Y., Ed.; World Scientific: Singapore, 1996; Vol. 2, p 137. (b) Ashcroft, A. T.; Cheetham, A. K.; Harris, P. J. F.; Jones, R. H.; Natarajan, S.; Sankar, G.;
Stedman, N. J.; Thomas, J. M. Catal. Lett. 1994, 24, 47.
26 16. Cao, D.; Bergens, H. J. Power Sources 2004, 134, 170.
17. (a) B. K. Teo, EXAFS: In Basic Principles and Data Analysis, Springer, Berlin, Germany, 1986.
(b) R. Prins and D. E. Koningsberger (eds.), In X-ray Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and XANES. Wiley-Interscience, New York, 1988.
18. (a) Camara, G. A.; Giz, M. J.; Paganin, V. A.; Ticianelli, E. A. J. Electroanal. Chem. 2002, 537, 21. (b) Russell, A. E.; Rose, A. Chem. Rev. 2004, 104, 4613. (c) Hills, C. W.; Nashner, M. S.;
Frenkel, A. I.; Shapley, J. R.; Nuzzo, R. G. Langmuir 1999, 15, 690. (d) Toshima, N.; Harada, M.; Yamazaki, Y.; Asakura, K. J. Phys. Chem. 1992, 96, 9927. (e) Toshima, N.; Harada, M.;
Yonezawa, T.; Kushihashi, K.; Asakura, K. J. Phys. Chem. 1991, 95, 7448. (f) Bian, C.-R.;
Suzuki, S.; Asakura, K.; Ping, L.; Toshima, N. J. Phys. Chem. B 2002, 106, 8587.
19. (a) Ankudinov, A. L.; Rehr, J. J.; Low, J. J.; Bare, S. R. J. Chem. Phys. 2002, 116, 1911. (b) Ankudinov, A. L.; Rehr, J. J.; Low, J.; Bare, S. R. Phys. Rev. Lett. 2001, 86, 1642. (c) Bazin, D.;
Sayers, D.; Rehr, J.; Mottet, C. J. Phys. Chem. 1997, 101, 5332.
20. Bazin, D.; Rehr, J. J. J. Phys. Chem. B 2003, 107, 12398.
21. Dassenoy, F.; Casanove, M.-J.; Lecante, P.; Pan, C.; Philippot, K.; Amiens, C.; Chaudret, B.
Phys. Rev. B 2001, 63, 235407.
22. (a) See for example the guidelines for data collection modes for EXAFS measurements and user controlled parameters: http://ixs.iit.edu/subcommittee_reports/sc/sc00report.pdf, (b) See for example the guidelines for errors reporting: http://ixs.iit.edu/subcommittee_reports/sc/err-rep.pdf.
23. Stern, E. A.; Newville, M.; Ravel, B.; Yacoby, Y.; Haskel, D. Physica B 1995, 208–209, 117.
24. Zabinsky, S. I.; Rehr, J. J.; Anukodinov, A. L.; Albers, R. C.; Eller, M. J. Phys. Rev. B 1995, 52, 2995.
25. Horsely, J. A. J. Chem. Phys. 1982, 76, 1451.
27 26. Ankudinov, A. L.; Rehr, J. J.; Simon, R. B. Chem. Phys. Lett. 2000, 316, 495.
27. Ayala, R.; Sánchez Marcos, E.; Díaz-Moreno, S.; Armando Solé, V.; Muñoz-Páez, A. J. Phys.
Chem. B 2001, 105, 7598.
28. Herron, M. E.; Doyle, S. E.; Pizzini, S.; Roberts, K. J.; Robinson, J.; Hards, G.; Walsh, F. C. J.
Electroanal. Chem. 1992, 324, 243.
29. Petrow, H. G.; Allen, R. J. US Patent No: 4044193, 1977.
30. Pârvulescu, V. I.; Coman, S.; Palade, P.; Macovei, D.; Teodorescu, C. M.; Filoti, G.; Molina, R.;
Poncelet, G.; Wagner, F. E. Appl. Surf. Sci. 1999, 141, 164.
31. Aricò, A. S.; Creti, P.; Kim, H.; Mantegna, R.; Giordano, N.; Antonucci, V. J. Electrochem. Soc.
1996, 143, 3047.
32. Warren, B. E. In X-ray Diffraction, Addison-Wesley: Reading, MA, 1996.
33. (a) Via, G. H.; Sinfelt, J. H. in: Y. Iwasawa (Ed,), X-ray Absorption Fine Structure for Catalysts and Surfaces, World Scientific: London, 1996. (b) Bazin, D.; Sayers, D.; Rehr, J. J. J. Phys.
Chem., 1997, 101, 11040.
Figure Captions
Figure 1. In situ XANES spectra at Pt LIII-edge for various reaction steps during the formation of Pt–Ru bimetallic NPs. The XANES patterns of reference compounds Pt foil, PtO2 and H2Pt(OH)6 were also shown.
Figure 2. Ru K-edge in Situ XANES spectra for various reaction steps during the formation of Pt–Ru bimetallic NPs. The XANES patterns of reference compounds Ru powder and RuO2 were also shown.
Figure 3. FT–EXAFS spectra at the Pt LIII-edge of various reaction steps during the formation of Pt–Ru bimetallic NPs, reference compounds: Pt foil, PtO2 and H2Pt(OH)6.
28 Figure 4. FT–EXAFS spectra at Ru K-edge of various reaction steps during the formation of Pt–Ru bimetallic NPs, reference compounds: Ru powder and RuO2.
Figure 5. XRD patterns of Pt–Ru/C nanoparticles obtained by a modified-Watanabe process.
Figure 6. TEM image of Pt–Ru/C nanoparticles obtained by a modified-Watanabe process.
Figure 7. Structural model deduced for the obtained Pt–Ru bimetallic NPs based on XAS structural parameters.
SCHEME 1. Schematic presentation of all the reaction steps during the formation of Pt–Ru bimetallic