Electrochemical and Spectroscopic Studies of
Graphene Nanoflakes with Functionalised Edges
Mailis Maria Lounasvuori
Thesis submitted in partial fulfilment of the requirements for the degree of
Doctor of Philosophy
UNIVERSITY COLLEGE LONDON
February 2017
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Declaration
I, Mailis Maria Lounasvuori, confirm that the work presented in this thesis is my own.
Where information has been derived from other sources, I confirm that this has been
indicated in the thesis.
Signature: ………………………………………………………………….
Date: ……………………….
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Abstract
The influence of surface functional groups on the electrochemical performance of
carbon electrodes was studied by using graphene nanoflakes (GNF), a well-defined
carbon nanomaterial. After characterisation with different techniques, GNF were used
to modify a boron-doped diamond (BDD) electrode and the influence of different edge
terminations on various redox probes was investigated using cyclic voltammetry (CV).
The outer-sphere redox probe ferrocenemethanol (FcMeOH) was found to be
unaffected by the presence of GNF at the electrode surface, confirming that GNF do
not inhibit electron transfer. When proton-coupled electron transfer was investigated, it
was shown that the acid-terminated GNF acted as a non-solution proton source and
sink.
The [Fe(CN6)]
3−/4− redox couple was found to be quasi-reversible and independent of
electrolyte pH at clean BDD and BDD modified with amide-terminated GNF. When
GNF were decorated with COOH functionalities, the reaction became less reversible
and pH-dependent. The reaction was also directly influenced by the electrolyte
concentration, with low concentrations causing the reaction to become more
irreversible.
Potential-induced dissociation of the carboxylic acid edge groups on GNF was
investigated with in situ spectroelectrochemistry combining potentiostatic control with
attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).
Applying a negative electrode potential led to the deprotonation of both electrode-
immobilised groups and species in solution. Acid dissociation was driven by an
increase in interfacial cation activity at the electrode surface that lowered the apparent
pKa of all species at or near the electrode.
Different methods of GNF attachment on the electrode surface were explored,
including direct attachment to gold via thiol edge groups and EDC-mediated amidation
reaction to form covalent bonds with a self-assembled monolayer (SAM) on gold.
Scanning tunnelling microscopy (STM) was used to verify the presence and probe the
orientation of GNF at the surface.
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Contents
Declaration ................................................................................................................... 2
Abstract ....................................................................................................................... 3
Contents ....................................................................................................................... 4
List of Symbols ............................................................................................................. 9
List of Abbreviations ................................................................................................... 11
List of Figures ............................................................................................................. 13
List of Schemes .......................................................................................................... 19
List of Tables .............................................................................................................. 20
List of Appendix Figures ............................................................................................. 22
List of Publications...................................................................................................... 23
1 Introduction.......................................................................................................... 24
1.1 Graphene ..................................................................................................... 24
1.1.1 Graphene synthesis ............................................................................... 28
1.1.2 Graphene Oxide..................................................................................... 30
1.1.3 Graphene Functionalisation ................................................................... 32
1.2 Electrochemistry of Graphene ...................................................................... 33
1.3 Graphene Nanoflakes................................................................................... 36
1.4 Acid-base Properties of Graphene-related Materials..................................... 40
1.4.1 Controlling the Protonation State of Electrode-Immobilised Species ...... 41
1.5 Methods of immobilising GNF on Electrode .................................................. 43
1.5.1 Drop-coating .......................................................................................... 43
Contents
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1.5.2 Spin-coating........................................................................................... 43
1.5.3 Self-assembly ........................................................................................ 44
1.6 Aim and Scope of the Thesis ........................................................................ 45
References for Chapter 1 ........................................................................................ 47
2 Experimental Theory and Techniques.................................................................. 56
2.1 Electrochemistry ........................................................................................... 56
2.1.1 Cyclic Voltammetry ................................................................................ 59
2.1.2 Differential Pulse Voltammetry ............................................................... 61
2.2 Infrared Spectroscopy................................................................................... 64
2.2.1 Attenuated Total Reflectance................................................................. 66
2.3 Scanning Tunnelling Microscopy .................................................................. 68
2.4 X-ray Photoelectron Spectroscopy................................................................ 70
2.5 Transmission Electron Microscopy ............................................................... 71
References for Chapter 2 ........................................................................................ 73
3 Characterisation of GNF ...................................................................................... 74
3.1 Introduction................................................................................................... 74
3.2 Experimental Methods .................................................................................. 75
3.2.1 Preparation of Complexed GNF............................................................. 76
3.2.2 X-ray Photoelectron Spectroscopy......................................................... 76
3.2.3 Transmission Electron Microscopy......................................................... 76
3.2.4 pH Titration ............................................................................................ 77
3.2.5 Electrochemical Experiments ................................................................. 77
3.2.6 ATR-FTIR .............................................................................................. 79
3.2.6.1 Stability of Aqueous Suspension of GNF ........................................ 79
3.2.6.2 Solution-Phase Characterisation of GNF ........................................ 79
3.3 Results and Discussion ................................................................................ 80
3.3.1 Transmission Electron Microscopy......................................................... 80
3.3.2 X-ray Photoelectron Spectroscopy......................................................... 81
3.3.3 Infrared Spectroscopy............................................................................ 83
Contents
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3.3.3.1 Stability........................................................................................... 86
3.3.4 pH Titration ............................................................................................ 86
3.3.5 In Situ pH Studies Monitored with Infrared Spectroscopy....................... 89
3.3.6 Electrochemistry of GNF without Redox Probes..................................... 91
3.3.7 Electrochemistry of FcMeOH at GNF-Modified Electrode....................... 95
3.3.8 Electrochemistry of Hydroquinone/Benzoquinone at GNF-Modified
Electrode.............................................................................................. 100
3.3.8.1 pH-Dependence of the Q/H2Q Reaction ....................................... 102
3.3.8.2 Exploring the Mechanism for Hydr
