Transparent carbon electrodes for spectroelectrochemical studies
This dissertation describes the assessment and use of carbon optically transparent electrodes (C-OTEs) based on pyrolyzed photoresist films (PPFs) as a platform for spectroelectrochemical investigations. C-OTEs are examined for use in UV-Vis spectroelectrochemistry and electrogenerated chemiluminescence and compared to non-transparent glassy carbon (GC) and the conventional transparent electrode indium tin oxide (ITO). Chapter 1 provides a general overview of transparent electrodes, carbon electrodes, and spectroelectrochemistry. Chapter 2 details a UV-Vis spectroelectrochemical investigation of electrogenerated graphitic oxides (EGO) on the surface of the C-OTE in the presence of KCl. X-ray photoelectron spectroscopy and time of flight secondary ion mass spectroscopy are used to determine EGO composition. Several supporting electrolytes are investigated to determine the mechanism of EGO formation. Chapter 3 details experiments to electrochemically access the exciton emission from self-assembled double-walled tubular J-aggregates via electrogenerated chemiluminescence (ECL). Optimization of ECL intensity with respect to the coreactant concentration and the supporting electrolyte pH is performed on opaque glassy carbon electrodes. ECL and fluorescence spectra are compared, and C-OTEs are utilized to determine the source of disagreement between the spectra. Chapter 4 describes the preparation and characterization (i.e. transparency, thickness, sheet resistance, rms roughness, and electroactive surface area) of C-OTEs and explores C-OTEs for general use in ECL under a variety of conditions. Simultaneous cyclic voltammograms and ECL transients are obtained for three thicknesses of PPFs and compared to non-transparent GC and the conventional transparent electrode ITO in both front face and transmission electrode cell geometries. Despite positive potential shifts in oxidation and ECL peaks, attributed to the internal resistance of the PPFs that result from their nanoscale thickness, the PPFs display similar ECL activity to GC, including the low oxidation potential observed for amine coreactants on hydrophobic electrodes. Overall, C-OTEs are promising electrodes for spectroelectrochemical applications because they yield higher ECL than ITO in both oxidative-reductive and reductive-oxidative ECL modes, are more stable in alkaline solutions, display a wide potential window of stability, and have tunable transparency for more efficient detection of light in the transmission cell geometry. Future directions for this research are discussed in Chapter 5, which outlines several approaches to designing and improving spectroelectrochemical sensors.