DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Peter Grauel :
The Ag/peroxodisulfate system
Interface and spatiotamporal pattern formation
Das Ag/Peroxodisulfat-System

 FU Logo

|Abstract| |Table of Contents| |More Information|

Abstract

In this thesis two aspects of peroxodisulfate reduction at Ag-electrodes are studied: On the one hand, the influence of peroxodisulfate on the double layer composition is investigated. On the other hand, the reduction of S2O82- serves as a model system for studying spatial pattern formation in systems with a negative differential resistance in the polarization curve. In particular the influence of the geometrical position of the reference electrode on pattern formation is examined. The system Ag/S2O82- (basic pH) and the subsystems were studied by using the SP-resonance shift technique (Surface Plasmons). Changes of the SP-resonance with potential are only detectable positive to a threshold potential. This threshold potential of the basic peroxodisulfate system was shifted 0.35V to more cathodic values in comparison to the corresponding basic sulfate system. An XPS-study showed that the SP-resonance changes of both systems are due to specifically adsobed OH- and an oxide like surface species O2-. The pzc ((point of zero charge) calculated from the XPS-data correlates with the threshold potential of the SP-study. An SEM-study of the peroxodisulfate system excluded surface roughening as source of the SP-resonance changes. The shift of the pzc (threshold potential) originates from the competition of the chemical oxidation of adsorbed OH- by S2O82- and the electrochemical reduction of formed OH. Both processes are very fast, whereas the desorption of specifically adsorbed OH- is much slower. For this reason an OH- coverage can build up at more cathodic values compared to the corresponding basic sulfate system, resulting also in a shift of the pzc to more cathodic values. The potential distribution in front of a rotating ring electrode was studied by using a potential microprobe. The reference electrode was placed in the sense of a classical Luggin capillary next to the working electrode. It was shown that such an arrangement will introduce a negative global coupling into the system which destabilizes homogeneous stationary states if the current-potential characteristics exhibits a negative differential resistance. As a consequence of this coupling standing potential waves exists in a certain parameter regime. The addition of an external resistance introduces a positive global coupling which can compensate the negative global coupling. In such a case potential patterns could not be detected any more.

Table of Contents

Download the whole PhDthesis as a zip-tar file or as zip-File

For download in PDF format click the chapter title

Inhaltsverzeichnis
I.Einleitung1
II.Grundlagen
II.1 Allgemeines zur nichtlinearen Dynamik 5
II.2 Allgemeines zur Reduktion von Peroxodisulfat an Metallelektroden 17
III.Grenzfläche
III.1 Literaturübersicht 36
III.2 Experimentelle Methoden 41
III.2.1 SP-Resonanzverschiebung(Surface Plasmons) 41
III.2.2 SEM (Scanning Electron Microscope) 51
III.2.3 XPS (X-ray Photoelectron Spectroscopy) 53
III.3 Ergebnisse 56
III.3.1 SP-Resonanzverschiebungsstudie 56
III.3.2 XPS-Studie 68
III.3.3 SEM-Studie 94
III.4 Diskussion 97
IV.Raumzeitliche Musterbildung
IV.1 Experimentelle Methoden 104
IV.2 Ergebnisse 109
IV.2.1 System ohne externem Widerstand 109
IV.2.2 Stationäre Strukturen 112
IV.2.3 System mit externem Widerstand 115
IV.3 Diskussion 117
V.Zusammenfassung
Liste häufig verwendeter Symbole und ihre Einheiten 139
Literaturverzeichnis 141

More Information:

Online available: http://www.diss.fu-berlin.de/1999/43/indexe.html
Language of PhDThesis: german
Keywords: Ag; peroxodisulfate; pzc; specific adsorption; stationary potential pattern
DNB-Sachgruppe: 30 Chemie
Date of disputation: 05-May-1999
PhDThesis from: Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin
First Referee: Prof. Dr. Gerhard Erl
Second Referee: Prof. Dr. Jürgen Dohrmann
Contact (Author): grauel@fhi-berlin.mpg.de
Contact (Advisor): krischer@fhi-berlin.mpg.de
Date created:13-Jul-1999
Date available:24-Aug-2000

 

|| DARWIN|| Digitale Dissertationen || Dissertation|| German Version|| FU Berlin|| Seitenanfang ||

Mail-Icon Fragen und Kommentare an:
darwin@inf.fu-berlin.de

© Freie Universität Berlin 1999