From photocatalysis to optoelectronic switches [Elektronische Ressource] : studies of visible light active photoelectrodes based on surface-modified titanium dioxide / vorgelegt von Radim Beránek

Radim

Informations

• Publié par: friedrich-alexander-universitat_erlangen-nurnberg
• Publié le: 01 janvier 2007
• Nombre de lectures: 24
• Langue: English
• Poids de l'ouvrage: 11 Mo

Extrait

From Photocatalysis to Optoelectronic Switches:
Studies of Visible Light Active Photoelectrodes Based on
Surface-Modified Titanium Dioxide






Den Naturwissenschaftlichen Fakultäten
der Friedrich-Alexander-Universität Erlangen-Nürnberg
zur
Erlangung des Doktorgrades

vorgelegt von
Radim Beránek
aus D ěčín (Tschechien)


Als Dissertation genehmigt von den Naturwissenschaftlichen Fakultäten der
Universität Erlangen-Nürnberg




















Tag der mündlichen Prüfung: 13. Juli 2007
Vorsitzender der Promotionskommission: Prof. Dr. Eberhard Bänsch
Erstberichterstatter: Prof. Dr. Horst Kisch
Zweitberichterstatter: Dr. Ulrich Nickel

Acknowledgements
I wish to thank Prof. Dr. Horst Kisch for the supervision of this work and many
fruitful discussions. I am particularly grateful for his advice, his trust in me, and his
generous support of my work.
Parts of this work would not have been possible without the help of several people.
Dr. Marcin Janczarek and Dr. Shanmugasundaram Sakthivel are acknowledged for the
synthesis of powders used in Chapter 3. Bernhard Neumann (Hahn-Meitner-Institut,
Berlin) is gratefully acknowledged for surface photovoltage measurements, their
interpretation and fruitful discussions. The work presented in Chapter 8 has profited
immensely from discussions with Dr. Wojciech Macyk and Dr. Konrad Szaci łowski. I
thank Dr. Marc Gärtner for his help with many experiments especially in the early
stage of my research, for valuable discussions and for correcting the German version
of the Summary. Dariusz Mitoraj is acknowledged for photocatalytic experiments and
for discussions. I thank also Christina Wronna for elemental analyses, Susanne
Hoffman for XRD measurements, Regina Müller for TGA analyses, Siegfried Smolny
for surface area measurements, Helga Hildebrand for XPS measurements, Anja
Friedrich for SEM and EDX analyses, Prof. Patrik Schmuki and
Prof. Sannakaisa Virtanen for allowing to perform the impedance measurements in
their labs, and Jan M. Macak and Dr. Julia Kunze for discussions. Manfred Weller,
Peter Igel and their colleagues from the “Werkstatt” are acknowledged for the
construction of photoelectrochemical cells and assistance with technical problems.
I am also indebted to Dr. Matthias Moll for his manifold help, Uwe Reißer for his help
with electronic equipment, Ronny Wiefel for glass work, and to Dr. Jörg Sutter for
computer assistance.
Many thanks to all my colleagues for contributing to the very good atmosphere in
the group – Marc, Marcin, Gerald, Müge, Ayyappan, Sakthi, Joachim, Sina, Dai,
Marco, Guillermo, Long, Darek, Przemek and Francesco – and also to all my friends
outside the institute, especially from the KHG.
I am very grateful towards my parents for their lifelong love and encouragement,
and I dedicate this work to them.
Last but not least, I would like to thank Ewa for her love and support.

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Die vorliegende Arbeit entstand in der Zeit von Oktober 2003 bis Mai 2007 am
Institut für Anorganische Chemie der Universität Erlangen-Nürnberg unter Anleitung
von Herrn Prof. Dr. Horst Kisch.
2  
Contents
Acknowledgements.............................................................................................. 1
Contents................................................................................................................ 3
Symbols and Abbreviations................................................................................ 5
1. Introduction .................................................................................................. 9
2. Literature .................................................................................................... 15
2.1 Fundamentals of Semiconductor Physics .......................................................15
2.1.1 Energy Band Model..........................................................................................15
2.1.2 Optical Properties of Semiconductors ..............................................................19
2.2 Photoelectrochemistry of Semiconductors .....................................................23
2.2.1 Semiconductor/Electrolyte Interface................................................................23
2.2.1.1 The Model of Gerischer23
2.2.1.2 Charge and Potential Distribution at the Interface..................................................26
2.2.1.3 The Energy Position of Band Edges .......................................................................30
2.2.2 Photoinduced Processes at Semiconductors in Electrolytes.............................32
2.2.2.1 Compact Semiconductor Electrodes33
2.2.2.2 Nanostructured Semiconductor Electrodes.............................................................35
2.2.2.3 Semiconductor Photocatalysis ................................................................................38
2.3 Nitrogen Doping/Modification of TiO ..........................................................40 2
2.3.1 Preparation Methods.........................................................................................40
2.3.2 Nitrogen Doping and the Origin of Visible-Light Activity..............................41
2.3.3 Photoelectrochemical Studies...........................................................................43
2.3.4 A Novel Low-Bandgap Titania ........................................................................44
3. Photocurrent and Surface Photovoltage Investigations of Low-Bandgap
Nitrogen-Modified TiO .................................................................................... 46 2
3.1 Introduction.....................................................................................................46
3.2 Experimental...................................................................................................46
3.3 Results and Discussion ...................................................................................49
3.3.1 Optical and Structural Characterization ...........................................................49
3.3.2 Surface Photovoltage Measurements................................................................50
3.3.3 Photocurrent Measurements.............................................................................53
3.3.4 Mechanism of Visible-Light Formic Acid Degradation...................................58
3.4 Conclusions60
4. Surface-Modified Anodic TiO Films for Visible Light Photocurrent 2
Response............................................................................................................. 61
4.1 Introduction.....................................................................................................61
4.2 Experimental...................................................................................................61
4.3 Results and Discussion ...................................................................................65
4.3.1 Structure and Composition ...............................................................................65
34.3.2 Photocurrent Measurements.............................................................................67
4.3.3 Flatband Potential Determination ....................................................................70
4.3.4 Mechanism of Photocurrent Generation ..........................................................73
4.4 Conclusions ....................................................................................................74
5. Tuning the Optical and Photoelectrochemical Properties of Surface-
Modified TiO 75 2
5.1 Introduction75
5.2 Experimental...................................................................................................76
5.3 Results and Discussion...................................................................................79
5.3.1 Optical and Structural Characterization........................................................... 79
5.3.2 Determination of Band Edges..........................................................................89
5.3.3 Photocurrent Measurements.............................................................................94
5.4 Conclusions ..................................................................................................100
6. Surface-Modified Transparent Nanocrystalline Films......................... 101
6.1 Introduction101
6.2 Experimental.................................................................................................101
6.3 Results and Discussion.................................................................................103
6.3.1 Structural and Optical Properties ...................................................................103
6.3.2 Spectroelectrochemical Measurements..........................................................104
6.3.3 Photocurrent Measurements...........................................................................108
6.4 Conclusions111
7. Comparative Discussion 112