Novel Electroanalytical Tools for Probing Electrochemically Generated Surface Nanobubble Characteristics

Abstract

Gaseous surface nanobubbles are produced in numerous electrochemical reactions of utmost economic and industrial importance. Despite the need to understand surface nanobubble characteristics and dynamics for continued improvement of gas-evolving electrochemical applications, a detailed physico-chemical description of surface nanobubbles remains at large. Nanobubbles are inherently difficult to study due to their complex and poorly understood properties and due to a lack of specialized electroanalytical tools required for continued investigation. This dissertation describes the use and development of novel electroanalytical tools for continued surface nanobubble characterization. A detailed overview of surface nanobubble properties and state-of-the-art analytical tools for bubble detection is provided in Chapter 1. Chapter 2 reports on the effects of surfactants on nanobubble nucleation dynamics using single molecule fluorescence microscopy. Generally, the adsorption of surfactants at the gas-water interface of surface nanobubble increases the rate of nucleation leading to more bubble production on the electrode surface. Furthermore, the adsorption of surfactant molecules changes the interfacial properties of the nanobubble and alters the molecular interactions of fluorophore molecules with the bubble surface. Thus, in Chapter 3, the gas-water interface at a surface nanobubble is systematically changed using surfactants of different chain length, charge, and counter ions to reveal the dominate properties governing fluorophore-bubble behavior. These studies show that electrostatics appear to dominate molecular dynamics at the gas-water interface of a nanobubble.Chapter 4 describes the development of off-axis darkfield microscopy for imaging a single nanobubble at a carbon nanoelectrode. This innovative imaging platform permits correlated electrochemical and optical detection for new insights into nanobubble characteristics previously inaccessible from state-of-the-art nanoelectrochemistry such as nucleation and dissolution dynamics. Broadly, off-axis darkfield microscopy enables the integration of traditional electrochemical probes such as nanoelectrodes and nanopores into a simple, label-free imaging platform. Finally, Chapter 5 details the early stages of developing darkfield enabled electrochemical microscopy for imaging transient electrochemical events using off-axis darkfield microscopy as an optical sensor/reporter.