Developing in Situ Electrochemical Techniques to Understand Mechanisms of Bubble Formation at Aqueous Electrochemical Interfaces

Abstract

Many electrochemical water treatment techniques (e.g. nitrate reduction, reactive oxygen species production, direct contaminant oxidation/reduction) rely on the electrochemical reactions that occur at the solid-liquid-gas triple-phase boundary layer, where gas species could be reactants, products, or undesired by-products. Developing foundational knowledge of the mechanisms by which surface bubbles form and how they impact chemical reactivity at surfaces would enhance the optimization and sustainability of electrified water treatment processes. The overall research goal is to develop in situ scanning electrochemical microscopy (SECM) to improve the microscopic understanding of how gas bubbles nucleate, form, grow, and migrate at solid–liquid interfaces. An important subset of gas-involving or gas-evolving, interfacial electrochemical reactions produces gas molecules dissolved in solution that can nucleate as small nanobubbles on electrode surfaces. These bubbles can grow to macroscopic sizes and interfere with chemical processes by blocking reactants from reaching the electrode-electrolyte interface, or by increasing turbulent mixing via leaving the surface. SECM is used to map the bubble formation mechanisms on the interface and to quantify the chemical species (reactant and product) concentration profile within the diffusion layer of the electrode surface. Here we will use oxygen reduction reaction (ORR) to hydrogen peroxide and nitrate reduction reaction (NO3RR) to ammonium as two model systems to investigate how SECM could help us understand chemical reaction mechanisms at aqueous electrochemical interfaces.