Polymer electrolyte membrane degradation and oxygen reduction in fuel cells [Elektronische Ressource] : an EPR and DFT investigation / vorgelegt von Alexander Panchenko

Panchenk

Informations

• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2004
• Nombre de lectures: 39
• Poids de l'ouvrage: 3 Mo

Extrait

POLYMER ELECTROLYTE MEMBRANE DEGRADATION
AND OXYGEN REDUCTION IN FUEL CELLS:
AN EPR AND DFT INVESTIGATION




Von der Fakultät Chemie der Universität Stuttgart zur
Erlangung der Würde eines Doktors der Naturwissenschaften
(Dr. rer. nat.) genehmigte Abhandlung




vorgelegt von

Dipl.-Chem. Alexander Panchenko
aus Jarowoje, Russland




Hauptberichter: Prof. Dr. Emil Roduner
Mitberichter: Prof. Dr. Hermann Stoll



Tag der mündlichen Prüfung: 12.10.2004

INSTITUT FÜR PHYSIKALISCHE CHEMIE
DER UNIVERSITÄT STUTTGART

Oktober 2004

































2
Eidesstattliche Erklärung

Ich versichere, dass ich diese Dissertation selbstständig verfasst und nur die angegebenen
Quellen und Hilfsmittel verwendet habe.



Stuttgart, 28.07.2004. Alexander Panchenko





















Prüfungsvorsitzender: Prof. Dr. Thomas Schleid
Hauptberichter: Prof. Dr. Emil Roduner
Mitberichter: Prof. Dr. Hermann Stoll
Tag der mündlichen Prüfung: 12.10.2004

3


4CONTENTS

CONTENTS

CONTENTS............................................................................................................................... 5
Abbreviations ......................................................................................................................... 7
List of figures 9
List of tables 14
1 INTRODUCTION............................................................................................................ 15
1.1 General introduction and main objectives....................................................................... 15
1.2 Organization of the Dissertation ..................................................................................... 18
2 FUNDAMENTALS .......................................................................................................... 19
2.1 Selected issues of the fuel cell technology...................................................................... 19
2.1.1 Electrochemical background .................................................................................... 20
2.1.2 Fuel cell components................................................................................................ 26
2.1.2.1 Membranes........................................................................................................ 26
2.1.2.2 Electrodes 30
2.1.3 Water management................................................................................................... 32
2.2 Oxygen reduction on Pt catalysts.................................................................................... 34
2.2.1 Reduction pathways ................................................................................................. 34
2.2.2 Background of the Oxygen Reduction Reaction...................................................... 37
2.2.2.1 O ....................................................................................................................... 37 2
•2.2.2.2 OH radical........................................................................................................ 38
2.2.2.3 H O .................................................................................................................. 39 2 2
2.2.2.4 H O.................................................................................................................... 39 2
3 EXPERIMENTAL AND THEORETICAL METHODS ............................................. 40
3.1 Description of experiments ............................................................................................. 40
3.1.1 Electron Paramagnetic Resonance ........................................................................... 40
3.1.1.1 Spin trapping technique..................................................................................... 43
3.1.2 SQUID experiments ................................................................................................. 45
3.1.2.1 Relevant examples of magnetism in matter ...................................................... 45
3.2 Theory description – the DFT approach ......................................................................... 49
3.2.1 VASP calculations.................................................................................................... 54
3.2.2 Gaussian 98 calculations .......................................................................................... 55
4 RESULTS AND DISCUSSION....................................................................................... 57
4.1 Fuel cell components....................................................................................................... 57
5CONTENTS

4.1.1 Gas Diffusion Electrodes ......................................................................................... 57
4.1.2 Pt catalyst supported on Vulcan XC-72 ................................................................... 64
4.1.3 Membranes ............................................................................................................... 68
4.1.3.1 Degradation of membrane components............................................................. 68
4.2 In situ fuel cell................................................................................................................. 74
4.2.1 Electrochemical characterization of the fuel cell ..................................................... 76
4.2.2 Water management................................................................................................... 78
4.2.3 In situ spin trap studies............................................................................................. 79
4.2.3.1 Anode side......................................................................................................... 81
4.2.3.2 Cathode side ...................................................................................................... 86
4.3 Oxygen reduction ............................................................................................................ 98
4.3.1 Uncoordinated O-containing species ....................................................................... 98
4.3.2 Adsorption properties of the O-containing species in the absence of water ............ 99
4.3.2.1 O molecule....................................................................................................... 99 2
4.3.2.2 O atom............................................................................................................. 106
•4.3.2.3 OH radical 109
•4.3.2.4 OOH radical ................................................................................................... 112
4.3.2.5 H O ................................................................................................................ 115 2 2
4.3.3 Influence of coadsorbed water ............................................................................... 115
4.3.3.1 O with two coadsorbed water molecules ....................................................... 116 2
•4.3.3.2 OH with two coadsorbed water molecules .................................................... 118
4.3.4 Relevance for fuel cells .......................................................................................... 120
5 SUMMARY..................................................................................................................... 125
ZUSAMMENFASSUNG....................................................................................................... 132
ACKNOWLEDGEMENT ..................................................................................................... 142
CURRICULUM VITAE ........................................................................................................ 144
BIBLIOGRAPHY .................................................................................................................. 145


6ABBREVIATIONS

Abbreviations

A 501 Polyethersulfone reacted with bis(4,4’-diethylamino)benzophenone
ACF Activated Carbon Fibers
ACM Adiabatic Connection Method
CCM Catalyst Coated Membrane
DBNBS 3,5-dibromo-4-nitrosobenzene-sulfonic acid
DEPMPO 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide
DFT Density Functional Theory
DMFC Direct Methanol Fuel Cell
DMPO 5,5-dimethyl-1-pyrroline-N-oxide
EELS Electron Energy Loss Spectroscopy
EPR Electron Paramagnetic Resonance
FEP-g-PSA Poly(tetrafluoroethylene-co-hexafluoropropylene) grafted with
poly(styrenesulphonic acid)
GDE Gas Diffusion Electrode
GGA Generalized Gradient Approximation
HF Hartree Fock
IRAS Infrared Reflectance-Absorption Spectroscopy
KS Kohn and Sh