CAREER: Confined Ionomeric Systems and Imaging of Ionic Distribution

非技术概述含离子聚合物（离聚物）是为许多重要应用开发的材料的组成部分，例如能量转换-储存、水净化、生物分离等。能量转换装置（如氢燃料电池）中的离聚物允许离子传导和发电。利用氢燃料电池可以极大地有益于环境，因为它在发电时不会排放任何有害气体（如二氧化碳，一氧化碳）。然而，由于使用昂贵的离聚物和催化剂，这种生态友好的技术在经济上不可行。此外，关于离聚物在厚（几十微米厚）材料中的行为有很多数据可用，但离聚物在非常薄（小于一微米厚）的材料中的行为仍然不是很好理解。薄的离聚物层具有差的离子传导性，这负面地影响能量转换和存储装置的性能。如果对催化剂界面处离聚物的纳米级性质没有充分的了解，就无法设计出更有效的下一代离子传导材料。为了满足这些需求，该项目将系统地研究质子传导离聚物如何与低成本催化剂（贵金属含量较低）相互作用，以及这些相互作用如何影响纳米薄膜中的离子传导环境。这种理解将导致化学合成的努力，设计新的离聚物，可以提高离子导电性在较薄的材料。 该项目将解决理解纳米聚合物的技术挑战，并推进现有知识。它将有助于使生态友好型氢燃料电池更高效、更便宜;帮助改进其他能量转换和存储设备（例如电池、超级电容器）;并提高生活质量。 这项工作也将有助于在STEM领域教育和培训各级学生（包括女性和代表性不足的少数民族），并激励他们从事技术和社会重要的职业。技术概述随着未来对更薄的能量转换和存储设备的需求不断增加，离聚物限制和界面现象的研究将变得更加重要。与本体膜相比，离聚物在薄膜限制下（例如在离聚物-催化剂薄界面处）表现得非常不同。纳米尺度的离子传导行为决定了基于燃料电池的装置的能量效率。该项目的目的是系统地探讨逐步变化的影响，在离聚物的约束和区分的离子传导行为的nanoconfined和散装材料作为离聚物材料的厚度，离聚物结构，催化剂的性质，和水合作用的函数。离子-催化剂-水的相互作用和局部水合环境的特征将在亚微米厚的质子交换离聚物在低铂族金属（低PGM）催化剂层上的阵列的膜中被定性地探索。通过结合纳米级离子传导环境的定性图像与质子传导率的定量值，将获得对界面质子传导的真正洞察。 离聚物材料的深度轮廓成像（在掺入比率荧光探针后）将提供关于跨材料厚度的性质分布（例如质子浓度轮廓）的信息。由于与薄离聚物膜相关的问题（限制、界面相互作用、不良连接的离子域、差的质子传导性）不同于本体膜，因此将化学合成一系列新的离聚物，旨在改善受限系统中的质子传导。离聚物结构内大环部分的存在将允许形成具有受控直径的孔和离子传导通道，这将提供额外的质子传导途径并促进纳米薄膜离聚物膜中的质子传导。该项目的教育目标是：1）通过教育和激励初中，高中，本科和研究生以及博士后研究人员，和2）通过对家庭和成年人的宣传，促进公众对可持续能源的认识和社会行为。该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响评审标准。

NON-TECHNICAL SUMMARYIon 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 SUMMARYAs 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.