CAREER: Confined Ionomeric Systems and Imaging of Ionic Distribution

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

NON-TECHNICAL SUMMARY Ion containing polymers (ionomers) are integral parts of materials developed for many important applications, such as energy conversion- storage, water purification, bioseparation, and others. Ionomers in an energy conversion device (such as hydrogen fuel cell) allow conduction of ions and generation of electricity. Utilizing hydrogen fuel cells can greatly benefit the environment since it does not emit any harmful gas (such as carbon dioxide, carbon monoxide) while generating electricity. However, such an eco-friendly technology is not economically viable due to the expensive ionomers and catalysts used. Also there is much data available on ionomer behavior in thick (several tens of micron thick) materials, but it is still not very well understood how ionomers behave in very thin (less than a micron thick) materials. Thin ionomer layers suffer from poor ion conductivity which negatively impacts the performance of energy conversion and storage devices. Without a sound understanding of nanoscale properties of ionomers at catalyst interfaces, more efficient, next-generation ion conducting materials cannot be designed. To address these needs, this project will systematically study how proton conducting ionomers interact with low-cost catalysts (with lower content of precious metals) and how those interactions impact the ion conduction environment in nanothin films. This understanding will lead a chemical synthesis effort to design new ionomers that can improve ion conductivity in thinner materials. This project will address technical challenges in understanding polymers at nanoscale and advance the existing knowledge. It will contribute to potentially making eco-friendly hydrogen fuel cells more efficient and cheaper; aid improvement of other energy conversion and storage devices (e.g. batteries, supercapacitors); and improve the quality of life. This work will also contribute to educating and training students (including women and underrepresented minorities) at all levels in STEM areas and inspire them toward technologically and societally important careers. TECHNICAL SUMMARY As the future demand for thinner energy conversion and storage device continually increases, ionomer confinement and interfacial phenomena studies continue to become more important. Ionomers behave very differently under thin film confinement (e.g. at ionomer-catalyst thin interfaces) as compared to bulk membranes. Nanoscale ion conduction behavior determines the energy efficiency of fuel cell based devices. The project aims to systematically probe the impact of gradual changes in ionomer confinement and distinguish the ion conduction behavior of nanoconfined and bulk materials as a function of ionomeric material thickness, ionomer structure, nature of catalyst, and hydration. Ionomer-catalyst-water interactions and characteristics of local hydration environment will be qualitatively explored in sub-micron thick films of an array of proton exchanging ionomers over low-Platinum group metal (low-PGM) catalyst layers. By combining the qualitative picture of nanoscale ion conduction environment with quantitative values of proton conductivity, a true insight into interfacial proton conduction will be obtained. Depth profile imaging of ionomeric materials (upon incorporation of ratiometric fluorescent probes) will offer information about distribution of properties (such as proton concentration profile) across the thickness of materials. Since the issues associated with thin ionomer films (confinement, interfacial interactions, ill-connected ionic domains, poor proton conductivity) are different from bulk membranes, a new range of ionomers will be chemically synthesized aiming to improve proton conduction in confined systems. The presence of macrocyclic moieties within ionomer structure will allow the formation of pores and ion conducting channels with controlled diameter, which will offer additional proton conduction pathways and facilitate proton conduction in nanothin ionomer films. The project's educational objectives are to: 1) prepare a diverse, future energy workforce by educating and inspiring middle school, high school, undergraduate and graduate students and post-doctoral researchers, and 2) contribute to public awareness and societal behavior regarding sustainable energy through outreach for families and adults. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.