Untersuchung der Metall/Elektrolyt-Grenzfläche mit Oberflächenröntgenbeugung

Schmidberger, J.

Book/Report

FZJ-2019-01793

Untersuchung der Metall/Elektrolyt-Grenzfläche mit Oberflächenröntgenbeugung

Schmidberger, J. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3335, 140 p. (1996)

Please use a persistent id in citations: http://hdl.handle.net/2128/21800

Report No.: Juel-3335

Abstract: In this work the structure of the metal/electrolyte interface was characterized by $\textit{in-situ}$ X-ray surface diffraction (XRSD). For this purpose an electrochemical cell was developed which allowed the simultaneous application of the XRSD technique and the method of cyclic voltammetry. The cell is constructed in such a way that it operates in a thin layer mode during the X-ray scattering experiments and is filled with electrolyte for the recording of cyclic voltammograms. With this cell the following metal/electrolyte interfaces were investigated: Au(100)/aqueous HClO$_{4}$, Au(100)/aqueous H$_{2}$SO$_{4}$, Pt(100)/aqueous HClO$_{4}$, Pt(111)/aqueous H$_{2}$SO$_{4}$. In all cases the single crystal surfaces are unreconstructed under the given experimental conditions and exhibit a certain island coverage and vacancy density depending on the surface orientation. No anion adsorption effect could be detected by XRSD except in the case of the Au(100)/aqueous H$_{2}$SO$_{4}$ interface. The analysis revealed an ordered commensurable adsorption layer of sulfate or hydrogensulfate ions with an coverage of about (35±10)%. However, no definite adsorption structure could be determined as shown in the discussion. On the basis of the results of the clean single crystal surfaces in contact with an electrolyte the structure and electrochemical behaviour of copper underpotential deposition (UPD) on Au(100) and ruthenium deposition on Pt(100) and Pt(111) were characterized. The copper UPD on Au(100) was chosen as an example of an (1x1)-adsorption. In contrast to the metal deposition systems investigated before this system allowed for the first time the observation of an ordered commensurable metal adsorption layer by XRSD under in-situ electrochemical conditions. Furthermore, the anion effect on the structure of the copper UPD on Au(100) was studied in aqueous perchloric acid, aqueous sulfuric acid andin mixtures of both.Detailed experiments with cyclic voltammetry and XRSD were performed. The investigations showed that in presence of H$_{2}$SO$_{4}$ the copper UPD occurs in a two-step process: first a Cu$^{+}$ ion layer is formed on the Au(100) surface, than the complete discharge occurs. The second step is not observed in pure aqueous perchloric acid. The observed effects have been discussed and interpreted also und er consideration of results from STM and QCMB investigations of this system. The investigations of the ruthenium deposition on Pt(100) occured in perchloric acid while the experiments on Pt(111) were performed in sulfuric acid. In both cases that ruthenium is deposited in the highly coordinated four-fold-hollow and three-fold-hollow sites, respectively, and form a monoatomically high adsorption layer in a commensurable (1x1)-structure. Thus, the XRSD experiments show that the structure of the initial stages of the ruthenium deposition on platinum as well as the copper UPD on gold single crystal surfaces occurs according to the structure of the substrate lattice. The XRSD results of the ruthenium deposition on Pt(111) in aqueous H$_{2}$S$O_{4}$ are in good agreement with STM measurements of this system. The comparison of the results obtained by XRSD and STM demonstrates that both techniques reveal partly the same but also complementary information on the interface structure. Therefore, only the consideration of both techniques yields a profound knowledge of the interface structure and underlines the importance of XRSD for the understanding of electrocatalytic processes and the establishing of a correlationbetween structure and reactivity on an atomic scale.

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