CAREER: Elucidating Fundamental Structure-Property Relationships in Ionomer Nanomcomposites for Redox Flow Batteries

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NON-TECHNICAL SUMMARYThe research goal of this CAREER award is to develop novel nanocomposite materials with functionality that can overcome practical hurdles for large-scale energy storage technologies such as the redox flow battery. Inadequate ion selectivity in existing charged polymers utilized in redox flow batteries has motivated the incorporation of nanoparticles, a versatile approach for tuning a wide range of properties of polymers. However, the molecular-scale heterogeneity in these materials has confused structure-property relationships needed for the development of viable nanocomposite materials for flow batteries. To address this gap, the research component of this CAREER award focuses on advancing our understanding of fundamental polymer physics governing interactions between functionalized nanoparticles and charged polymers, and how these in turn alter resultant polymer architectures and bulk functional properties that are relevant for selective ion exchange. The design and synthesis of novel soft composite materials will be guided by these fundamental structure-property relationships to yield desirable molecular-scale interactions, thus enabling their functionality for energy storage applications. These findings and materials also have the potential to impact other critical modern technologies that utilize functional polymer membranes, such as water purification and energy delivery. These research efforts are closely tied to educational initiatives that aim to engage and inspire the next generation of engineers and scientists. Undergraduate and graduate students contributing to this project will be exposed to advanced materials synthesis and characterization techniques, equipping them with the interdisciplinary skills needed to address tomorrow's engineering challenges. Together with chemical engineering students at Clemson University, this award will develop and implement a STEM-based afterschool program, for students grades 6-8, that emphasizes scientific problem solving through the application of polymer science concepts to tackle hands-on tasks inspired by real-world challenges. Together with the research component, these educational and outreach programs seek to foster an inclusive approach to addressing STEM challenges that improves national technical and economic competencies, as well as helps to build a diverse, competitive, and innovative future workforce.TECHNICAL SUMMARYThe design of next-generation ionomer nanocomposites for redox flow batteries, a scalable energy storage technology, is hindered by an inadequate understanding of the underlying polymer physics governing ion transport in these charged materials. The complex morphology of existing materials exacerbates this by further confusing fundamental structure-property relationships, resulting in, to date, only marginal improvements in membrane performance. The research goal of this CAREER award is centered on addressing this fundamental knowledge gap by interrogating how polymer network structure and segmental dynamics impact technology-relevant performance properties of ionomer nanocomposites. This will be achieved by systematically varying the molecular weight, monomer architecture, and degree of sulfonation of a series of novel ion-conducting aromatic polymer composites (e.g., sulfonated poly(aryl ether ketone)s) containing functionalized nanoparticles. By tuning the molecular-level properties of the membrane, as well as the characteristics of the nanoparticles (e.g., surface functionalization, size, and loading), the role of morphology on membrane dynamics and ion transport can be elucidated. Segmental dynamics (localized motions and chain dynamics) of the hydrated composite membranes will be interrogated using both neutron spin echo and dielectric spectroscopy, where the latter experimental technique will also be used to characterize the motion of charge carriers, that is, water-mediated ion transport. In addition, 'bulk-scale' dynamics of the hydrated membranes will be captured using infrared spectroscopy and compared to the local membrane dynamics. These powerful, noninvasive spectroscopic techniques can be used to interrogate membrane dynamics over a wide range of length and time scales, providing insight into the impact of nanoparticle characteristics on the collective membrane segmental dynamics and ion diffusion. Performing such studies is critical to establishing comprehensive, fundamental relationships between nanoscale features of the ionomer nanocomposites and device-relevant performance properties. Poroelastic relaxation indentation will be employed to characterize the mechanical properties and the dynamics of solvent migration of the hydrated nanocomposite membranes, as these directly impact water-mediated ion transport in these materials. As the use of advanced functional polymers in membrane-based technologies continues to grow, the fundamental knowledge gained from this research has the potential to impact the design of new materials in areas such as water purification and energy storage and delivery. The research component of this CAREER award is closely integrated with educational initiatives that seek to improve diversity and inclusivity for STEM in the upstate South Carolina area through teaching, undergraduate research, outreach, and the implementation of a STEM-based afterschool program at a local middle school.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.