Coverage evolution of sulfur on Pt(111) electrodes: From compressed overlayers to well-defined islands

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• 作者：Sung ; Y.-E. ; et. al.
• 关键词：Pt(111) electrode ; Sulfur chemisorption ; Sulfur structures ; Thermodynamics of UPDH ; Under-potential deposition of hydrogen
• 刊名：Electrochimica Acta
• 出版年：1998
• 出版时间：November 1, 1998
• 年：1998
• 卷：44
• 期：6-7
• 页码：1019-1030
• 全文大小：738 K

文摘

The paper examines formation of a monolayer and submonolayers of S_chem on Pt(111) electrodes accomplished through its immersion in aqueous Na₂S solution. The S_chem monolayer, having the (1×1) structure at θ_Schem=1, can be gradually removed by oxidative desorption at E≥0.95 V, RHE, and the S_chem coverage can be precisely controlled. The S_chem layer suppresses the H_UPD and anion adsorption as well as it affects the oxide growth behavior on Pt(111). LEED data reveal that S_chem forms well-defined structures on Pt(111) for 0.50≥θ_Schem≥0.25: c(2×2) at θ_Schem=1/2, ()R30° at θ_Schem=1/3, and p(2×2) at θ_Schem=1/4; when θ_Schem≤0.20, structured islands of S_chem are observed. AES and CEELS data indicate that the adsorbed S is not present in an oxidized state; it is almost of atomic character with an incomplete negative charge due to partial charge transfer between S_chem and the Pt(111) substrate. Presence of S_chem influences thermodynamics of the H_UPD on Pt(111) resulting in less-negative values of ΔG_ads(S)(H_UPD). In the absence of S_chem, the H_UPD is enthalpy-driven whereas in the presence of S_chem it becomes entropy-driven. The Pt(111)–H_UPD bond energy is weaker in the presence of S_chem than in its absence, and this bond energy diminution may be assigned to local electronic effects arising from presence of S_chem.