SYNTHESIS OF NOVEL PERFLUORINATED ION EXCHANGE MEMBRANES AGAINST HYDROGEN PEROXIDE DEGRADATION IN ELECTROCHEMICAL ENERGY STORAGE DEVICES

Author

Elizabeth Waleade Salako, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2024

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Gao, Yong

Abstract

AN ABSTRACT OF THE DISSERTATION OFElizabeth W. Salako, for the Doctor of Philosophy degree in Chemistry, presented on March 27, 2024, at Southern Illinois University Carbondale. TITLE: SYNTHESIS OF NOVEL PERFLUORINATED ION EXCHANGE MEMBRANES AGAINST HYDROGEN PEROXIDE DEGRADATION IN ELECTROCHEMICAL ENERGY STORAGE DEVICES MAJOR PROFESSOR: Dr. Yong GaoThe continuous burning of fossil fuels to meet the energy needs of the ever-growing population has extensive and enduring effects on the environment, human health, and the economy. Adopting cleaner and more sustainable energy sources is crucial to reducing the impact and tackling the difficulties posed by climate change. Renewable energy, which is derived from sources that are naturally replenished, presents a compelling solution to address these pressing challenges. Due to the inherent intermittency of renewable energy available, which relies on weather conditions and daylight hours, incorporating energy storage technology into the power grid can effectively handle unforeseeable power demands.An ion exchange membrane (IEM) is an important part of electrochemical energy storage and conversion devices like fuel cells, flow batteries, and electrolyzers. Without it, these devices would not work properly. The IEM has significantly enhanced these devices by enabling higher operating temperatures and improving their durability and efficiency. The proton exchange membrane (PEM) has been greatly studied, with Nafion® (a product of DuPont) as the state-of-the-art membrane. Even though Nafion®, which belongs to the perfluorosulfonic acid (PFSA) group, has been commercialized, it suffers from low working temperatures, high cost, low tolerance to fuel impurities, and most importantly, degradation of the membrane over a short period of time. The membrane undergoes three main types of degradation: mechanical, thermal, and chemical degradation. Although the mechanical and thermal degradation of the membranes can be managed, the chemical degradation is a more intricate and challenging issue to address. The degradation of Nafion® occurs through the process of radical-induced disintegration of the polymer structure. This selectively targets the weakest points in the polymer structure, thereby fragmenting the polymer and leading to a loss of ionic conductivity. These vulnerable sites include carboxylic acid groups, C-S linkages, tertiary carbons, and fluoro-ether groups. Studies have shown the fluoro-ether groups to be more susceptible to hydroxyl radical attacks. In our aim to reduce membrane degradation, we designed and synthesized novel fluoro-monomers void of the fluoro-ether groups. We used the emulsion polymerization process in a high-pressure reactor to polymerize our synthesized monomers with a commercially available monomer to make different ionomers with -SO3H and -PO3H2 ion exchange groups. We measured the molecular weight of the polymers through the viscometry method. The mechanical properties of the polymers were not as great, and it became difficult to cast them into a thin film. Polytetrafluoroethylene (PTFE) films were used as a support for the polymers to make them stronger and to also measure their ion conductivities in comparison with NafionTM 115. Fenton’s test was employed to measure the susceptibility of the polymers to hydroxyl radical attack. Our polymers were not as good at conducting ions as NafionTM 115, but they were better at protecting against hydroxyl radical attacks, both at room temperature and higher temperatures. The results showed an inverse relationship between the number of fluoroalkyl ether groups present in the polymers and their resistance to hydroxyl radical attacks.