A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item RADIATION SYNTHESIS OF IONIC LIQUID POLYMER ELECTROLYTE MEMBRANE FOR HIGH TEMPERATURE FUEL CELL APPLICATIONS(2020) Mecadon, Kevin; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this thesis was to design, synthesize and analyze innovative anhydrous fuel cell membranes that can operate at temperatures above 100°C. Operating at this higher temperature region improves performance and reliability of fuel cells: increasing proton mobility, enhancing reaction kinetics, increasing catalysis activity and reducing carbon monoxide poisoning. Traditional polymer electrolyte membrane fuel cells (PEMFCs) do not operate efficiently above 100°C because water is used as a proton conductive medium though the Grotthuss hopping mechanism. Through substituting water with protic ionic liquids and grafting onto fluorocarbon films, a new proton conductive network solid state PEM has been developed. These membranes can perform at high temperature above 100°C. Polymers were selected for grafting based on the following properties: high proton conductivity, low electrical conductivity, high mechanical properties, high chemical resistance, and high temperature and humidity stability. The method used to synthesize these anhydrous polymer electrolyte membranes (PEMs) was radiation grafting using heterocyclic protic ionic liquid monomers and fluorocarbon substrates. PEMs were prepared at the Medical Industrial Radiation Facilities (MIRF) at the National Institute of Standards and Technology (NIST). MIRF is a 10.5 MeV electron beam accelerator, which was used to radiate the fluorocarbon substrate and then indirectly graft heterocyclic protic ionic liquids to create PEMs. After synthesis, the extent and uniformity of PEM composition was analyzed using FTIR microscopy, SEM/EDS, SANS and their proton conductivity as measured by EIS. Through this research, indirect radiation grafting was shown to covalently bond ionic liquids onto fluorocarbon substrates to synthesize PEMs. The resulting ionic liquid PEMs showed proton conductivities greater than 10-3 S/cm above 100°C that behaved independent of humidity. The ionic liquid PEMs also demonstrated a positive correlation of increasing proton conductivity with increasing temperatures above 100°C even after the PEMs are dehydrated. The chemical properties and structure of the grafted ionic liquids greatly affects the proton conductive mechanisms present in the PEMs. These trends found through the course of this research will help the development of future anhydrous PEM with higher proton conductivity, performance, and reliability.Item Polymer-Ionic Liquid Hybrid Electrolytes for Lithium Batteries(2012) Fisher, Aaron Steven; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intellectual Merit: The goal of this dissertation is to investigate the electrochemical properties and microstructure of thin film polymer electrolytes with enhanced electrochemical performance. Solid electrolyte architectures have been produced by blending novel room temperature ionic liquid (RTIL) chemistries with ionically conductive polymer matrices. A variety of microstructure and electrical characterization tools have been employed to understand the hybrid electrolyte's performance. Lithium-ion batteries are limited because of the safety of the electrolyte. The current generation of batteries uses organic solvents to conduct lithium between the electrodes. Occasionally, the low boiling point and high combustibility of these solvents lead to pressure build ups and fires within cells. Additionally, there are issues with electrolyte loss and decreased performance that must be accounted for in daily use. Thus, interest in replacing this system with a solid polymer electrolyte that can match the properties of an organic solvent is of great interest in battery research. However, a polymer electrolyte by itself is incapable of meeting the performance characteristics, and thus by adding an RTIL it has met the necessary threshold values. With the development of the novel sulfur based ionic liquid compounds, improved performance characteristics were realized for the polymer electrolyte. The synthesized RTILs were blended with ionically conductive polymer matrices (polyethylene oxide (PEO) or block copolymers of PEO) to produce solid electrolytes. Such shape-conforming materials could be lead to unique battery morphologies, but more importantly the safety of these new batteries will greatly exceeds those based on traditional organic carbonate electrolytes. Broader Impacts: The broader impact of this research is that it will ultimately help push forward an attractive alternative to carbonate based liquid electrolyte systems. Development of these alternatives has been slow; however bypassing the current commercial options will lead to not only safer and more powerful batteries. The polymer electrolyte system offers flexibility in both mechanical properties and product design. In due course, this will lead to batteries unlike any currently available on the market. RTILs offer quite an attractive option and the electrochemical understanding of novel architectures based upon sulfur will lead to further potential uses for these compounds.