La lecture en ligne est gratuite
Le téléchargement nécessite un accès à la bibliothèque YouScribe
Tout savoir sur nos offres
Télécharger Lire

Model electrodes for the electrooxidation of simple alcohols [Elektronische Ressource] : a DEMS study / Abd-el-Aziz Ali Abd-el-Latif Abd-el-Salehin

De
187 pages
Model electrodes for the electrooxidation of simple alcohols: a DEMS study Dissertation zur Erlangung des Doktorgrades (Dr. rer.nat) der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von Abd-El-Aziz Ali Abd-El-Latif Abd-El-Salehin aus Kairo, Ägypten Bonn, 2011 Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn Promotionskommission Erster Gutachter: Prof. Dr. Helmut Baltruschat Zweiter Gutachter: Prof. Dr. Klaus Wandelt Fachnaher Gutachter: Prof. Dr. Siegfried Waldvogel Fachfremder Gutachter: Prof. Dr. Karl Maier Tag der mündlichen Prüfung: 10 . 08 .2011 Ich versichere, dass ich diese Arbeit selbständig verfasst und keine anderen als die angegebenen Quellen und Hilfsmittel benutzt sowie die Zitate kenntlich gemacht habe. Bonn, 08.06.2011 Abd-El-Aziz Abd-El-Salehin For my Motherland (Egypt), Martyrs of El-Tahrir Square, My Parents, My Family Contents Chapter 1: Introduction 1.1 Fuel cells …………………………………………………………………….. 1 1.1.
Voir plus Voir moins



Model electrodes for the electrooxidation of
simple alcohols: a DEMS study



Dissertation
zur
Erlangung des Doktorgrades (Dr. rer.nat)
der
Mathematisch-Naturwissenschaftlichen Fakultät
der
Rheinischen Friedrich-Wilhelms-Universität Bonn




vorgelegt von

Abd-El-Aziz Ali Abd-El-Latif Abd-El-Salehin




aus

Kairo, Ägypten




Bonn, 2011















































Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät
der
Rheinischen Friedrich-Wilhelms-Universität Bonn








Promotionskommission

Erster Gutachter: Prof. Dr. Helmut Baltruschat
Zweiter Gutachter: Prof. Dr. Klaus Wandelt
Fachnaher Gutachter: Prof. Dr. Siegfried Waldvogel
Fachfremder Gutachter: Prof. Dr. Karl Maier





Tag der mündlichen Prüfung:

10 . 08 .2011










Ich versichere, dass ich diese Arbeit selbständig verfasst und keine anderen als die angegebenen
Quellen und Hilfsmittel benutzt sowie die Zitate kenntlich gemacht habe.

Bonn, 08.06.2011




Abd-El-Aziz Abd-El-Salehin































































For my Motherland (Egypt),
Martyrs of El-Tahrir Square,
My Parents,
My Family














Contents

Chapter 1: Introduction

1.1 Fuel cells …………………………………………………………………….. 1
1.1.1 History of fuel cell …………………………………………………………... 1
1.1.2 Importance of fuel cell ………………………………………………………. 1
1.1.3 Basics of fuel cell …………………………………………………………… 2
1.1.4 Types of fuel cell …………3
1.1.5 Fuel of PEM fuel cell ……4
1.2 Platinum as electrocatalyst in fuel cell ……………………………………… 4
1.2.1 Pt single crystals …………………………………………………………….. 4
1.2.1.1 Pt basal plane ………………………………………………………………... 5
1.2.1.2 High index surfaces of metals ………………………………………………. 6
1.2.2 Relaxation and reconstruction of clean single crystal surfaces ……………... 8
1.2.2.1 Relaxation ………………………………………………………………….... 9
1.2.2.2 Reconstruction ………………………………………………………………. 9
1.3 Fundamental of metal deposition ………10
1.3.1 Cu underpotential deposition (Cu UPD) …………………………………….. 12
1.3.1.1 Cu UPD on Pt basal planes ………………………………………………….. 12
1.3.1.2 t stepped surfaces ……………………………………………... 13
1.3.2 Ru deposition at Pt surfaces …………………………………………………. 13
1.3.2.1 Spontaneous deposition ……………………………………………………... 14
1.3.2.2 Forced deposition ……………………………………………………………. 14
1.3.2.3 Electrodeposition …………14
1.4 Differential electrochemical mass spectrometry (DEMS) setup and DEMS
cells …………………………………………………………………………. 15
1.4.1 DEMS history ………………………………………………………………. 15
1.5 Electrooxidation of simple molecules ………………………………………. 16
1.5.1 Electrooxidation of adsorbed CO …………………………………………… 16
1.5.2 Electrooxidation of methanol ……………………………………………….. 18
1.5.3 Electrooxidation of formaldehyde . ………………………………………..... 21
1.5.4 Electrooxidation of ethanol ………………………………………………...... 22

Chapter 2: Experimental work

2.1 Experimental techniques ……………………………………………………. 33
2.1.1 Cyclic voltammetry (CV) ……………………………………………………
2.1.2 Potential step ………………………………………………………………… 34
2.1.3 Deposition of Ru sub-monolayer at Pt stepped single crystals ………………
2.1.4 Preparation of Ru quasi single crystals ……………………………………… 36
2.1.5 Cu UPD ……………………………………………………………………… 37
2.1.6 Galvanic replacement ……………………………………………………….. 38
i 2.2 Chemicals, cleaning and electrodes …………………………………………. 38
2.2.1 Chemicals ……………………………………………………………………. 38
2.2.2 Cleaning of laboratory glassware …………………………………………… 41
2.2.3 Electrolytes ………………………………………………………………….. 41
2.2.4 Adsorption test ……………………………………………………………….
2.2.5 Cleaning and preparation of single crystals …………………………………. 42
2.2.5.1 Electrochemical cleaning ……………………………………………………. 42
2.2.5.2 Chemical treatment ………………………………………………………….. 43
2.2.5.3 Preparation of Pt single crystals ……………………………………………... 43
2.2.6 The conventional electrochemical glass cell “H-cell” ………………………. 44
2.2.7 Preparation of reference electrodes………45
2.2.7.1 Reversible hydrogen electrode (RHE) ………………………………………. 45
2.2.7.2 Pd/H electrode ……………46
2.2.7.3 Cu/CuSO electrode …………………………………………………………. 46 4
2.3 DEMS setup and DEMS cells ……………………………………………….. 46
2.3.1 DEMS setup …………………………………………………………………. 47
2.3.2 The DEMS cells……………………………………………………………… 48
2.3.2.1 Dual thin layer flow through cell …………………………………………….
2.3.2.2 New DEMS cell for bead crystal ………49
2.4 Calibration of DEMS ………………………………………………………... 50
2.4.1 DEMS calibration by electrooxidation of pre-adsorbed CO ………………... 50
2.4.2 Calibration curve for acetaldehyde (m/z = 29) and methylformate (m/z = 60) 51

Chapter 3: Electrooxidation of methanol and the mechanism of
methylformate formation

3.1 Introduction ………………………………………………………………….. 53
3.2 Results and discussion ……………………………………………………….
3.2.1 Kinetic of methanol esterification ………………………………………….... 53
3.2.1.1 Calibration of methylformate ……………………………………………….. 53
3.2.1.2 Methanol esterification in acidic media ……………………………………... 55
3.2.2 Electrooxidation of bulk methanol at a polycrystalline platinum electrode .... 58
3.2.2.1 Cyclic voltammetry …….................................................................................. 58
3.2.2.2 Potential step experiments …………………………………………………... 63
3.2.2.3 Electrooxidation of methanol adsorbate …………………………………….. 67
3.2.2.4 Potential hold experime69
3.2.2.5 Effect of supporting electrolyte ……………………………………………... 71
3.2.2.6 Discussions of methanol oxidation at Pt(pc)………………………………… 73
3.2.3 Electrooxidation at Pt single crystal electrodes................................................ 75
3.2.3.1 Electrooxidation of adsorbed CO …………………………………………… 75
3.2.3.2 Electrooxidation of bulk methanol at Pt(331) ……………………………….. 79
3.3 Conclusions ………………………………………………………………….. 83


ii Chapter 4: Electrooxidation of ethanol

4.1 Introduction ………………………………………………………………….. 89
4.2 Results and discussion ………………………………………………………. 90
4.2.1 Electrooxidation of bulk ethanol on Pt(pc) ………………………………….. 90
4.2.1.1 Effect of supporting electrolyte ……………………………………………... 90
4.2.1.2 Electrooxidation of deuterated ethanol ……………………………………… 92
4.2.1.3 Potential hold experiments …………………………………………………... 94
4.2.1.4 Potential step e96
4.2.2 Ethanol adsorbate species …………………………………………………… 99
4.2.2.1 Oxidation of ethanol adsorbate …………99
4.2.2.2 Reduction of ethanol adsorbate ……………………………………………... 100
4.2.2.3 Coverage of ethanol adsorbate …………………………………………….... 102
4.2.3 Effect of surface structure 103
4.2.4 Effect of Ru …………………………………………………………………. 114
4.3 Conclusions …………………………………………………………………. 116

Chapter 5: Cu UPD at Ru quasi single crystal

5.1 Introduction ………………………………………………………………….. 119
5.2 Results and discussion ………………………………………………………. 122
5.2.1 Characterization of Pt stepped single crystals ………………………………. 122
5.2.1.1 Blank voltammograms ………………………………………………………. 122
5.2.1.2 Cu UPD ……………………………………………………………………… 123
5.2.2 Characteristic CV of Ru quasi single crystal film …………………………... 126
5.2.2.1 Blank voltammograms for Ru/Pt basal planes ………………………………. 126
5.2.2.2 Blank voltammograms for Ru/Pt stepped single crystals …………………… 127
5.2.2.3 Cu UPD on Ru/Pt basal planes ……………………………………………… 128
5.2.2.4 Ru/Pt stepped single crystals 130
5.2.3 Electrodeposition of Cu under diffusion control ……………………………. 135
5.2.4 Pt sub-monolayer on Ru quasi single crystal film ………………………….. 138
5.2.4.1 Why not UPD deposition of Pt on Ru(ijkl)? ………………………………… 138
5.2.4.2 Galvanic replacement of Cu with Pt ……………………………………… 139 ML
5.2.4.3 Characterization of Pt/Ru/Pt single crystals ………………………………… 140
5.3 Conclusions ………………………………………………………………….. 142

Chapter 6: New DEMS cell applicable to different electrode sizes

6.1 Introduction 147
6.2 Description of the new cell ………………………………………………….. 147
6.3 Results and discussion ………………………………………………………. 149
6.3.1 Characteristic CVs of Pt single crystals in DEMS cell ……………………… 149
6.3.2 Calibration of DEMS setup 150
6.3.2.1 DEMS calibration by CO adlayer electrooxidation ...……………………….. 150
iii 6.3.2.2 DEMS calibration by formic acid electrooxidation...………………………... 151
6.3.2.3 by hydrogen evolution...…………………………………. 153
6.3.3 Electrooxidation of small organic molecules …………154
6.3.3.1 Electrooxidation of formic acid ……………………………………………... 154
6.3.3.2 Electrooxidation aldehyde ………156
6.3.3.3 Electrooxidation of methanol ……………157
6.4 Conclusions ………………………………………………………………….. 159

Chapter 7: Summary and outlook


















iv

Un pour Un
Permettre à tous d'accéder à la lecture
Pour chaque accès à la bibliothèque, YouScribe donne un accès à une personne dans le besoin