Kinetics of methanol electrooxidation on PtRu catalysts in a membrane electrode assembly [Elektronische Ressource] = Kinetik der Elektrooxidation von Methanol an PtRu Katalysatoren auf einer Membranelektrode / von Tanja Vidakovic

Mpi

Informations

• Publié par: otto-von-guericke-universitat_magdeburg
• Publié le: 01 janvier 2005
• Nombre de lectures: 36
• Poids de l'ouvrage: 2 Mo

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Kinetics of Methanol Electrooxidation on PtRu Catalysts
in a Membrane Electrode Assembly

Kinetik der Elektrooxidation von Methanol an PtRu
Katalysatoren auf einer Membranelektrode

Dissertation
zur Erlangung des akademischen Grades
Doktoringenieur
(Dr. - Ing)
von Dipl.-Ing. Tanja Vidakovi ć
geb. am 2. September 1970 in Požega, Serbia

genehmigt durch die Fakultät für Verfahrens- und Systemtechik
der Otto-von-Guericke-Universität Magdeburg

Gutachter: Prof. Dr.-Ing. habil. Kai Sundmacher
Prof. Dr. Mihai Christov
Prof. Dr. habil. Helmut Weiß
Promotionskolloquium am 17. 06. 2005
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Table of contents
Preface...........................................................................................................................................IV
Abstract..........VI
Zusammenfassung ..................................................................................................................... VII
1. Introduction ........................................................................................................................... 1
2. Experimental.......................................................................................................................... 6
2.1. Electrochemical cell...................................................................................................6
2.2. Reactants....................................................................................................................7
2.3. Electrocatalysts ..........................................................................................................7
2.4. Preparation of MEA7
2.5. Electrochemical measurements..................................................................................8
2.6. CO stripping voltammetry .........................................................................................9
2.7. Determination of ohmic resistance ............................................................................9
2.8. Comparison of steady state and quasi-steady state measurements ..........................10
2.9. Determination of geometric surface area.................................................................11
3. Electrochemical methods for the real surface area determination................................. 14
3.1. Hydrogen adsorption method...................................................................................15
3.1.1. Experimental approach ...........................................................................18
3.1.2. Determination of real surface area of unsupported Pt catalyst ...............19
3.2. CO adsorption method .............................................................................................21
3.2.1. Experimental approach25
3.2.2. Unsupported Pt catalyst ..........................................................................26
3.2.3. Unsupported PtRu catalyst......................................................................30
3.3. Conclusions..............................................................................................................38
3.4. Outlook ....................................................................................................................39
4. Kinetics of methanol oxidation........................................................................................... 40
4.1. Mechanism of methanol electrooxidation – Literature overview............................41
4.2. Catalyst characterization..........................................................................................52
4.3. Activity in methanol oxidation – Experimental findings.........................................55
4.3.1. Influence of flow rate..............................................................................55
4.3.2. Influence of methanol concentration ......................................................58
4.3.3. Electrochemical impedance spectroscopy ..............................................60
4.3.4. Influence of temperature.........................................................................62
4.4. Mechanism and rate expression for methanol oxidation .........................................64 III
4.5. Simulated vs. experimental data ..............................................................................67
4.6. Influence of PtRu loading ........................................................................................71
4.6.1. Catalyst characterisation .........................................................................71
4.6.2. Activity towards methanol oxidation......................................................72
4.7. Influence of support .................................................................................................72
4.7.1. Cyclic voltammetry in the absence of methanol.....................................73
4.7.2. Activity towards methanol oxidation73
4.8. Conclusions..............................................................................................................74
4.9. Outlook ....................................................................................................................75
5. Relation between catalyst synthesis and activity in methanol electrooxidation ............ 76
5.1. Methods for nanoparticle preparation......................................................................77
5.2. Experimental............................................................................................................81
5.2.1. Catalyst synthesis....................................................................................81
5.2.2. Physical methods86
5.2.3. Electrochemical methods........................................................................87
5.3. Characterisation of catalysts87
5.3.1. Physical methods87
5.3.2. CO stripping............................................................................................94
5.3.3. Cyclic voltammetry in absence of methanol...........................................99
5.4. Catalyst activity in methanol oxidation .................................................................102
5.4.1. Current vs. time - stability test ..............................................................106
5.4.2. Electrochemical impedance spectroscopy ............................................107
5.5. Influence of conditioning, support and leaching....................................................108
5.5.1. ......................................................................108
5.5.2. Influence of support ..............................................................................111
5.5.3. Influence of leaching.............................................................................112
5.6. Conclusions............................................................................................................115
5.7. Outlook ..................................................................................................................116
6. Concluding Remarks......................................................................................................... 117
7. References .......................................................................................................................... 119
Appendix I .................................................................................................................................. 124
Appendix II.. 128 IV
Preface
This thesis was done at the Max-Planck Institute for Dynamics of Complex Technical
Systems in Magdeburg, during my 2 years stay at the Institute. However, the beginning of my
work in this topic was in Belgrade at the Department of Physical Chemistry and
Electrochemistry, Faculty of Technology and Metallurgy. There I made my first steps in the
field of methanol oxidation under supervision of Prof. Snezana Gojkovi ć. I would like to
thank Prof. Snezana Gojkovi ć for understanding my decision to continue my work and to
defend my thesis in Magdeburg. So, in 2002 I decided to come to Germany, join the group of
Prof. Sundmacher and continue work on the same topic but in a different kind of system. In
order to do so, I first had to get a leave of absence from my Faculty in Belgrade, where I have
been working as a teaching assistant since 1995. At this point I would like to express my
gratitude to my colleagues and Professors at the Department of Physical Chemistry and
Electrochemistry who took over and distributed my normal teaching duties in this time and
allowed me to concentrate only on the research. I owe special thanks to my Diploma and
Master Thesis supervisor Prof. Branislav Nikolić, who supported my idea to come to
Magdeburg in spite of his concerns that it will double my work on the thesis.
For my stay in Magdeburg I would like to thank Prof. Sundmacher, who accepted my
application to work on one of the projects in his group related to the kinetics of methanol
oxidation and also the Max-Planck Society, which provided me a scholarship during my stay.
Prof. Sundmacher was a supervisor who tried to teach m