Date of Award

2014

Document Type

Open Access Dissertation

Department

Electrical Engineering

First Advisor

MVS Chandrashekhar

Abstract

Microbial fuel cells (MFCs) are seen as a promising complementary technology to alleviate the exponentially increasing worldwide energy demand. MFCs use bacteria to extract energy from biomass, where choice of electrode materials has a strong impact on energy extraction and efficiency. Graphene, a single monolayer of carbon with exceptional electrical conductivity and high surface area, is seen as a promising material with the potential of improving charge transfer and bacterial adhesion. To probe this reactivity, a novel means of hydrogenation of graphene by electrochemistry is demonstrated.

In this thesis, electrochemical hydrogenation of epitaxial graphene (EG), graphene grown on silicon carbide (SiC), shows new pathways of carbon chemistries for electrodes and hydrogen storage. The difficulty with reacting hydrogen with graphene is the need for atomic hydrogen, as hydrogen gas, H2, does not react directly with carbon. H+ ions in acidic electrolyte readily react with negatively biased graphene, revealing the reactivity of graphene and forming localized insulator-like states. Incorporating hydrogen into graphene, forming graphane, has also been shown as a means to create an engineered bandgap in semi-metal graphene, from ~0-3.5eV, allowing for traditional device architectures. This hydrogenation was shown to be thermally and electrochemically reversible, ideal for batteries and fuel cells, and history dependent, impacting H loading.

An electrochemical impedance model was developed for the electrochemical cell, with reactivity of graphene shown to be strongly dependent on defect density, edges, grain boundaries and point defects in the material, impacting the degree of hydrogenation. Addition of metal catalysts was shown as a means to overcome electrochemical hydrogenation defect dependence by lowering activation potential and offering additional pathways for hydrogen to adsorb.

Lastly, the biocompatibility of bacteria on graphene was confirmed by fluorescence confocal microscopy. Bacterial sensing by graphene demonstrated, with the ability to monitor bacterial activity through changes in EG electrical conductivity, allowing for its use as sensitive, real-time sensor for detecting biological activity. With biocompatibility established, graphene, as well as other carbon materials can be investigated by electrochemistry for optimization of MFCs.

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