Research Information System
American Chemical Society Spring 2024, Louisiana, United States Of America, 17 - 21 March 2024, (Summary Text)
Plasma-liquid systems are usually comprised of an atmospheric-pressure plasma electrode and a liquid surface, which can have a bubbly and irregular, or a smooth surface. When coupled with a metal counter electrode immersed in the liquid, this configuration has been shown to form capable electrochemical systems that can degrade recalcitrant pollutants, and when reactive gases are used, can create unique gas-liquid reaction pathways for important processes such as N2 fixation and CO2 utilization. Recently, such plasma-liquid systems have been used to conduct controlled organic reactions.
When in contact with a liquid, plasmas deliver radicals into the solution. The transport and lifetime of these radicals play a major role in the observed kinetics and selectivity. Despite the different frequencies, plasma electrode shapes, gas flow rates and applied powers utilized in literature, most plasma sources in plasma-liquid systems deliver a radical density to the interface that is much higher than the current density in conventional electrochemistry. Consequently, the observed rate constants of some of the plasma-assisted processes mentioned above have been found to fall in a rather narrow range of values, despite the vast differences in plasma sources. This is an indication of mass transport playing a crucial role in the observed kinetics. Since only a few rate constants for plasma produced radicals and organic compounds have been published, organic electrochemistry using plasmas should have the goals of determining the rate constants and elucidating the intrinsic kinetics, so that a fundamental understanding of such systems can be established. Taking out the effect of mass transfer is therefore required. In electrochemistry, there are two ways of establishing this goal: 1) using a kinetically-limited electrode (e.g. a rotating disk, which has been incorporated into plasma-liquid systems) or by using a reaction-diffusion model that captures the mass transfer phenomena effectively. The latter is also useful for optimizing the performance of most plasma-liquid systems.
This talk will focus on the development of a simple mass transfer model for plasma-liquid reactions. Regimes of mass transfer limitations and important parameters will be discussed. Estimation of the mass transfer coefficient will also be presented. The extensive use of the model will be demonstrated by using pinacol coupling as an example.