Exploring the First Steps in Core鈥揝hell Electrocatalyst Preparation: In Situ Characterization of the Underpotential Deposition of Cu on Supported Au Nanoparticles

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• 作者：Stephen W. T. Price ; Jonathon D. Speed ; Prabalini Kannan ; Andrea E. Russell
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：December 7, 2011
• 年：2011
• 卷：133
• 期：48
• 页码：19448-19458
• 全文大小：1169K
• 年卷期：v.133,no.48(December 7, 2011)
• ISSN：1520-5126

文摘

The underpotential deposition (upd) of a Cu shell on a non-Pt nanoparticle core followed by galvanic displacement of the Cu template shell to form core鈥搒hell electrocatalyst materials is one means by which the Pt-based mass activity targets required for commercialization of PEM fuel cells may be reached. In situ EXAFS measurements were conducted at both the Au L₃ and the Cu K absorption edges during deposition of Cu onto a carbon-supported Au electrocatalyst to study the initial stages of formation of such a core鈥搒hell electrocatalyst. The Au L₃ EXAFS data obtained in 0.5 mol dm^鈥? H₂SO₄ show that the shape of the Au core is potential dependent, from a flattened to a round spherical shape as the Cu upd potential is approached. Following the addition of 2 mmol dm^鈥? Cu, the structure was also measured as a function of the applied potential. At +0.2 V vs Hg/Hg₂SO₄, the Cu²⁺ species was found to be a hydrated octahedron. As the potential was made more negative, single-crystal studies predict an ordered bilayer of sulfate anions and partially discharged Cu ions, followed by a complete/uniform layer of Cu atoms. In contrast, the model obtained by fitting the Au L₃ and Cu K EXAFS data corresponds first to partially discharged Cu ions deposited at the defect sites in the outer shell of the Au nanoparticles at 鈭?.42 V, followed by the growth of clusters of Cu atoms at 鈭?.51 V. The absence of a uniform/complete Cu shell, even at the most negative potentials investigated, has implications for the structure, and the activity and/or stability, of the core鈥搒hell catalyst that would be subsequently formed following galvanic displacement of the Cu shell.