Electrochemistry Promoted by Plasma-solvated Electrons in Non- Aqueous Solutions
Abstract
In conventional electrochemistry, reactions occur at the interface of a metal electrode and an electrolytic solution through electron transfer between the immersed metal and solution ions. Plasma electrochemistry describes reactions at the interface of an electrical discharge in a gas and a solution, including the injection of electrons from the plasma into the liquid phase. Unlike solid electrode systems, the electrons are unbounded and solvate in solution, leading to one of the most strongly reducing species but at a distance from any solid electrode. The solvated electron can promote reactions that are challenging using conventional metal electrodes such as the reduction of carbon dioxide (CO2) to carbon anion radicals and the generation of detached metal nanopowders. However, to date the majority of the field has focused on water as the liquid solution, where there are two significant challenges. First, the formation of water vapor can lead to undesired reactions in the gas (plasma)-phase that either impede electron injection or serve as an impurity for synthesis. Second, solvated electrons react with water via second order recombination which is kinetically fast and competes with any other desired reaction. Both of these issues could be addressed by moving away from water as a solvent. The goal of this research project is to establish the scientific underpinnings of electrochemistry promoted by plasma-injected solvated electrons in a non-aqueous solvent, with a specific focus on alcohols and emerging exotic liquids known as deep eutectic solvents (DES). The proposed research will build on prior research accomplishments by the team through multiple ARO-supported grants. These accomplishments include: (i) development of an in-situ diagnostic to interrogate solvated electrons at a plasma-liquid interface termed total internal reflection absorption spectroscopy (TIRAS); (ii) kinetic analysis of solvated electron chemistry through model reactions and reaction modeling; and (iii) applications of solvated electron chemistry for CO2 reduction and detached metal nanopowder synthesis. This research will extend the capabilities that have previously been established to non-aqueous solvents to study two principle Objectives: Objective 1 is to understand how plasma-injected solvated electrons behave in alcohols, including glycerol and ethylene glycol, and alcohol-derived DES, such as glyceline and ethaline. TIRAS measurements will be used to characterize solvated electrons and to extract essential properties, including their penetration depth and lifetime. Objective 2 is to understand the reaction behavior of solvated electrons with both model (e.g., chloroacetate) and Army-relevant (e.g., CO2 and metal salt) reactants. Bulk product measurements via various analytical techniques and modeling will be used to quantify reduction efficiency and kinetically- or transport-limited behavior. Potential reaction pathways Ð and high-value products Ð not possible in water will be identified for both CO2 and hard-to-reduce metals such as aluminum. These two Objectives will advance fundamental understanding of the behavior of plasma-injected solvated electrons in non-aqueous solvents, and by limiting the contribution of vapor to gas(plasma)-phase chemistry and second order recombination in the solution, clarify and direct solvated electron chemistry for reactions of interest. Long term, we foresee improved understanding of plasma-injected solvated electrons in a wide-range of solvents leading to a broad range of applications including not only synthesis, but also environmental remediation and energy conversion/storage. Ultimately, we predict that important scientific problems in electrochemistry and radiation chemistry can be addressed and new applications can be realized by taking advantage of the interactions between plasmas and liquids.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 22, 2022
- Source ID
- W911NF2310010
Entities
People
- David B Go
Organizations
- Army Contracting Command
- United States Army
- University of Notre Dame