Graphene electrochemistry: fundamentals through to electroanalytical applications

Brownson, D.A.C. (2013) Graphene electrochemistry: fundamentals through to electroanalytical applications. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Graphene is reported to possess a range of unique and highly desired properties and consequently has potential to revolutionise the field of electrochemistry if diligently employed as a new-generation electrode material. Graphene potentially represents the world’s thinnest electrode material, but there are experimental parameters to be overcome: the first problem is how to electrically wire/connect to the graphene sample(s) as to obtain the reported benefits; the second issue is how to reduce aggregation of graphene sheets back to their lowest energy conformation, that is, graphite, due to the strong π–π interactions between the graphene sheets; the third and final limitation is that various fabrication routes produce graphene to differing qualities, a factor that must be considered when exploring its fundamental electrochemical properties and electroanalytical implementation. This thesis reports on the fundamental electrochemical characterisation and resultant electroanalytical applicability of utilising graphene as a novel electrode material. The thesis consists of four key contributions, each developing on the knowledge gained from the previous. Chapters 1 through to 3 give an overview of the relevant fundamental electrochemical concepts with which this thesis is concerned. Chapter 4 provides a ‘snap-shot’ of the state of the graphene literature from 2010 (upon the commencement of this work), from which successive chapters follow the chronological development and investigation of graphene as produced through a variety of synthesis methods, gradually building a complete picture and understanding of the electrochemistry of graphene and the implications of its properties towards the fabrication and implementation of graphene as an electroanalytical sensor substrate. IV | P a g e Chapter 5 details the relevant experimental information and the full physicochemical characterisation of the various graphene materials utilised within this work. Chapters 6 and 7 utilise graphenes that are fabricated via a ‘top-down’ approach, which is most commonly employed in the literature, where in order to ‘connect to’ the graphene a liquid suspension is immobilised onto a suitable electrode surface. Chapter 6 uses surfactant-modified graphene and investigates, for the first time, the influence that such surfactants have on the observed electrochemistry. Chapter 7 uses pristine graphene in solution and considers; the aspects of various ‘coverages’ of graphene, the supporting electrode substrate, and how the formation of few and multiple layered graphene structures can influence the observed response. These parameters are overlooked within the current literature. Chapter 8 utilises graphene that is fabricated via a ‘bottom-up’ Chemical Vapour Deposition approach, which gives rise to high quality single layer graphene domains that, once efficiently ‘housed’ in order to connect to the graphene, allow the electrochemical exploration of monolayer graphene to be realised and be compared to quasi-graphene and defect abundant graphene structures for the first time. This approach allows the structure of graphene to be correlated with that of the electrochemical response for the first time. Critically, this work unambiguously demonstrates that the electrochemical response is edge plane like defect dependent. The final part of this thesis (Chapter 9) utilises a range of modified graphenes including novel three-dimensional (3D) structures (a graphene foam and graphene paste) and functionalised graphene (graphene/graphitic oxide), with the effects of said modifications explored towards the fundamental electrochemical and electroanalytical properties obtained. The first part of this chapter reports the electrochemistry of a novel freestanding 3D graphene V | P a g e foam and, for the first time, critically compares this to a freestanding 3D carbon foam alternative. It is demonstrated that the graphene foam gives rise to beneficial voltammetric responses in non-aqueous media, namely ionic liquids. This chapter also explores the use of a graphene paste electrode and demonstrates that the voltammetric response is no better than that of a graphite based paste electrode. Last, the use of graphene/graphitic oxide as an electrode material is explored and shown to give rise to unique voltammetric signatures, which are coverage dependant and can be utilised as a means of characterising the successful production of graphene through the reduction of graphene/graphitic oxide (as commonly utilised within the current electrochemical literature). Furthermore, it is shown that the unique voltammetry observed at graphene/graphitic oxide modified electrodes can be used beneficially for electrocatalytic processes. This thesis demonstrates that, within the graphene electrochemical literature, control experiments are often an overlooked comparison, which are needed for the electrochemical response of graphene to be understood and before the benefits of graphene can be claimed in such instances where superiority is ‘demonstrated’.