Plasma Interactions with Non-Aqueous Liquids: Formation and Behavior of Solvated Electrons in Ethylene Glycol

Recent advances in plasma electrochemistry, where the conventional working electrode of an electrolytic cell is replaced by an atmospheric-pressure gas discharge, have opened up new avenues for chemical reactions and processes. When the plasma is biased negative relative to the liquid, the plasma injects solvated electrons (e^-_sol) at the plasma-liquid interface, as well as producing other highly reactive species including ions, photons, and radicals. The e^-_sol facilitate chemical reactions, with corresponding faradaic efficiencies surpassing 100% under particular conditions. However, plasma electrochemistry in aqueous media presents challenges such as water vaporization and rapid second-order recombination of e^-_sol with water molecules that diminishes reactions with other solution species. Non-aqueous solvents can address these issues, especially those with low-vapor pressure and limited recombination of e^-_sol. Here, we study the behavior of e^-_sol in ethylene glycol as a model non-aqueous solvent. Employing an in-situ diagnostic technique known as total internal reflection absorption spectroscopy (TIRAS) as well as pulse radiolysis, we verify the formation of e^-_sol at the plasma-liquid interface by their light absorption. The relationship between current density and e^-_sol is predicted theoretically and confirmed experimentally, enabling empirical estimations of the penetration depth and interfacial concentration of e^-_sol. Through this investigation, we aim to provide insights into fundamental interactions between non-equilibrium plasmas and non-aqueous liquids, with implications for a wide range of applications in environmental, energy, and materials science.