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Fundamentals of electrochemistry of graphene and other 2D materials

García-Miranda Ferrari, Alejandro (2019) Fundamentals of electrochemistry of graphene and other 2D materials. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Currently there is a global interest in the application of 2D materials such as graphene, graphene oxide (GO), reduced graphene oxide (rGO), 2D hexagonal boron nitride (2D-hBN), MoSe2, MoS2, WSe2, antimonene and phosphorene within electrochemical applications. Some of those applications range from their use as sensors and energy storage/generation devices, including its use as an electrochemical supercapacitor, lithium/sodium ion batteries and as anodes and cathodes within fuel cells, to name just a few. This global interest is due to the unique beneficial properties of the 2D materials over traditional electrochemical materials. As a result, there is a need to fundamentally understand how these 2D materials behave as electrodes at the single layer scale within electrochemical systems, and develop enhanced 2D materials into useful 3D structures, e.g. as 3D printed structures/electrodes. The discovery and/or confirmation of the fundamental electrochemical properties of these 2D materials could enable its application in several areas, such as additive manufacturing, electronics, and energy storage/generation for electrochemical sensor platforms. There is a huge potential for this knowledge to be usefully exploited within sensing and energy sectors and beyond. This thesis reports the electrochemistry of graphene and other 2D nanomaterials from a fundamental point of view with thorough physicochemical characterisation and resultant electrochemical applicability of using 2D materials as electrodes. Chapter 1 gives an overview of the fundamental concepts of electrochemistry and 2D materials related to this thesis. Chapter 2 details relevant experimental information used in this thesis. 8 Chapter 3 compares methods to determine the electroactive area of CVD grown graphene, which is important and novel contribution to those experimentalist using this and other electrode materials in order to benchmark their electrode platform. Chapter 4 demonstrates the origin of electron transfer properties of edge and basal plane sites on true graphene (polymer-free transferred and single layer). Chapters 5 and 6 study, for the first time, the applicability and structural integrity of CVD graphene sheets towards the water splitting reactions depending on the number of layers, scan rate and voltage applied towards energy applications, indicating that mono- and few-layer CVD graphene are not suitable electrode materials towards the HER and the OER. Such work is of fundamental importance when graphene surfaces are use either “as is” or as the basis of catalyst as used in the HER/OER (Chapter 5 and 6 respectively). Chapter 7 explores the introduction of physical linear defects (PLDs) on the surface of monolayer hexagonal-boron nitride films (2D-hBN), in order change from an insulator to a semiconductor material, tailoring its electrochemical properties. Physicochemical, computational and electrochemical characterisation techniques are applied to identify/explain the change in the electrochemical response from the change in surface morphology. 2D-hBN typically is considered an electrochemical insulator, however this thesis reports that through implementation of physical defects (simple surface modifications) the bandgap changes from ca. 6.11 eV to ca. 2.36 eV, giving rise to electrochemically useful signatures towards RuHex, Fe+2/+3 and the HER.. Chapter 8 explores the use of different lateral flake sizes of graphitic powders in paste electrodes, applying the knowledge from Chapter 4, to obtain enhanced sensor devices by using smaller lateral flake sizes graphitic materials. 9 Lastly, chapter 9 explores the additive manufacturing of Graphene/PLA composites, namely thin films, 3D printable filaments and 3D printed electrodes, demonstrating that useful low cost 3D printable electrode can be manufactured and applied towards electroanalytical applications.

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