CAREER: Confined Ionomeric Systems and Imaging of Ionic Distribution

非技术性聚合物(离聚体)是为能量转换储存、水净化、生物分离等许多重要应用而开发的材料的组成部分。能量转换装置(如氢燃料电池)中的离聚体允许离子传导和发电。利用氢燃料电池可以极大地有利于环境，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体和催化剂，这种环保技术在经济上并不可行。此外，关于离聚体在厚(几十微米厚)材料中的行为也有很多数据，但离聚体在非常薄(小于一微米厚)材料中的行为仍然不是很清楚。薄离聚体层的离子导电性差，对能量转换和存储设备的性能产生了负面影响。如果不充分了解催化剂界面离聚体的纳米级特性，就不可能设计出更高效的下一代离子导电材料。为了满足这些需求，本项目将系统地研究质子传导离聚体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膜中的离子传导环境。这一认识将导致化学合成努力设计新的离聚体，以提高较薄材料的离子导电性。这个项目将解决在纳米尺度上理解聚合物的技术挑战，并促进现有知识的发展。它将有助于潜在地使环保型氢燃料电池更高效、更便宜；有助于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。这项工作还将有助于STEM地区各级学生(包括女性和代表性不足的少数民族)的教育和培训，并激励他们从事具有技术和社会重要性的职业。技术总结随着未来对更薄的能量转换和存储设备的需求不断增加，离聚体限制和界面现象研究继续变得更加重要。离聚体在薄膜限制下(例如，在离聚体-催化剂薄界面上)的行为与体膜相比有很大的不同。纳米尺度的离子传导行为决定了基于燃料电池的器件的能量效率。该项目旨在系统地探索离聚体限制的逐渐变化的影响，并区分纳米限制材料和块状材料的离子传导行为作为离聚体材料厚度、离聚体结构、催化剂的性质和水合作用的函数。在低铂族金属(Low-PGM)催化层上的质子交换离聚体的亚微米厚薄膜中，将定性地探索离聚体-催化剂-水的相互作用和局部水化环境的特征。通过将纳米尺度离子导电环境的定性图像与质子电导率的量化值相结合，将对界面质子导电有一个真实的了解。离子材料的深度分布成像(在加入比率荧光探针后)将提供有关材料厚度上的性质分布(如质子浓度分布)的信息。由于与离聚体薄膜相关的问题(限制、界面相互作用、连接不良的离子结构域、较差的质子导电性)不同于体膜，将通过化学方法合成一系列新的离聚体，以改善受限体系中的质子传导。离聚体结构中大环结构的存在将允许形成孔径可控的孔和离子传导通道，这将提供额外的质子传导途径，促进纳米硫蛋白离聚体薄膜的质子传导。该项目的教育目标是：1)通过教育和激励初中生、高中生、本科生和研究生以及博士后研究人员，培养一支多样化的、未来的能源劳动力队伍；2)通过面向家庭和成年人的宣传活动，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智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.