Metastable AuxRh100鈥?i>x Thin Films Prepared by Pulsed Laser Deposition for the Electrooxidation of Methanol

详细信息    查看全文

• 作者：R茅gis Imbeault ; David Reyter ; S茅bastien Garbarino ; Lionel Rou茅 ; Daniel Guay
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：March 1, 2012
• 年：2012
• 卷：116
• 期：8
• 页码：5262-5269
• 全文大小：415K
• 年卷期：v.116,no.8(March 1, 2012)
• ISSN：1932-7455

文摘

Metastable Au_xRh_100鈥?i>x thin films were prepared by crossed beam pulsed laser deposition on two different substrates. High kinetic-energy deposition conditions were used (0.1 Torr He, 5.5 cm target-to-substrate distance). The films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, and their electrocatalytic activities for the electrooxidation of methanol were assessed by linear sweep voltammetry in 1 M NaOH. All films are made of a single fcc phase compound. For 40 < x < 85 at %, the lattice parameter deviates slightly from that expected from Vegard鈥檚 law. The XRD patterns of Au_xRh_100鈥?i>x/C and Au_xRh_100鈥?i>x/Si did not evolve over a period of 1 year, indicating that the solid solution is kinetically stable. However, as expected from the Au鈥揜h binary phase diagram, heat treatment of Au₅₀Rh₅₀/C at 500 掳C in Ar during 24 h leads to decomposition of the metastable fcc phase and the formation of Rh and Au. X-ray photoelectron spectroscopy revealed that the Au surface composition closely follows the Au bulk content. The binding energy difference between the Rh 3d_5/2 and Au 4f_7/2 core level peaks shifts from 223.3 to 222.4 eV as x is increased from 5 to 95, indicating that a surface alloy is formed between Au and Rh. In the presence of methanol, Au_xRh_100鈥?i>x/C with x = 25, 50, and 75 shows a methanol oxidation peak (a₂) in a potential region (ca. 鈭?.12 V vs Hg/HgO), where pure Au and Rh do not exhibit any electrocatalytic activity for methanol oxidation. The current of peak a₂ increases with the methanol concentration. The formation of a surface alloy significantly improves the electrocatalytic activity for methanol oxidation by providing OH^{鈥?/sup> species at lower potential (by 400 mV) compared with pure Au.}