Computer Modeling of Proton Conduction in Metal-Organic Frameworks

技术概述化学部和材料研究部为该奖项提供资金。它支持理论研究和教育，目的是通过开发和应用一种新的模拟方法来模拟金属有机框架中的质子传导。固体和多孔材料中的质子传导是燃料电池技术的一个重要基础过程。目前对燃料电池的研究主要集中在质子交换膜上，其中电解质是Nafion或其他磺化聚合物。由于只有在高度水合作用下才能获得高质子导电性，目前燃料电池的最高工作温度受到水的凝结点的限制。金属有机框架是概念上不同的分离材料，可以在高温和低湿环境下传输质子。金属有机骨架的主要优点之一是可以通过合适的有机配体来修饰其孔的内表面，使其具有亲水性和酸性，从而可以在分子水平上控制质子传导。本研究项目的重点是在几种化学和结构不同的金属有机框架中进行质子传导的分子水平建模，所有这些都对燃料电池技术的可能应用具有相当大的兴趣。具体的研究重点是：1)吸附在纳米通道中的水分子的质子传导；2)吸附在纳米通道中的含氮分子的质子传导；3)功能化金属-有机框架中的质子传导。由于许多分子结构的键拓扑动态变化和周围化学环境的复杂性，质子传导对当前的计算方法提出了挑战。质子传导的精确表征需要对潜在的多体相互作用的物理完整表示以及相关相空间的广泛采样。这两个组成部分的严格结合最终会导致对控制质子输运热力学和动力学的自由能图景的正确描述。将开发一种新的计算方法，通过将基于从头算的质子跳跃表示与框架-框架和框架-来宾相互作用的准确描述相结合，来应对这一挑战。这将为金属-有机框架中控制质子传输的机制提供分子水平的见解，这是合理设计新的导电金属-有机框架结构的第一步，也是必要的一步，这种结构可以在更高的温度和更低的相对湿度下工作，用于下一代燃料电池。研究生和本科生以及博士后将参与研究，并将获得理论，物理和材料化学的坚实基础。在这个项目中开发的计算方法将集成在Amber中，这是一个流行的分子动力学模拟包。外联部分还包括PI继续参与研究学者计划，该计划为来自全国各地的高中生提供在加州大学圣地亚哥分校进行暑期研究的机会。化学部和材料研究部为本奖项提供资金。它支持与燃料电池技术作为替代能源相关的综合理论和计算研究和教育计划。不断增加的能源需求及其对环境的影响对今后使用石油和天然气等自然资源构成了严格的限制。最近在开发替代能源方面投入了相当大的努力，例如将化学能转化为直接可用形式的燃料电池。例如，氢燃料电池利用一种基本的化学反应，首先从氢分子中提取电子，在阳极产生质子，然后通过外部电路产生直流电转移到阴极。与此同时，质子通过可渗透膜从阳极传输到阴极，在那里它们与电子团聚形成氢分子，随后与氧反应生成水。最终的结果就是化学能转化为电能。由于氢燃料电池的整体产品是水和热，因此就环境问题而言，氢燃料电池是清洁技术。燃料电池尚未找到更广泛应用的原因之一与它们的效率有关，这在很大程度上取决于质子从阳极到阴极快速穿过膜的能力。目前使用的膜的特殊性质是发展更高效燃料电池的主要障碍。该项目的主要目标是使用计算机模拟来表征在一种被称为金属有机框架的新型材料中决定质子传导的分子机制。金属有机框架包含有机分子，作为无机簇之间的桥梁，形成高度多孔的三维结构。由于微观孔隙和通道的存在，金属有机框架因此可以用作燃料电池技术中的有效分离器，其中质子可以通过中间的载体分子或通过框架本身从阳极穿梭到阴极。拟议的项目侧重于在几种化学和结构不同的金属有机框架中进行质子传导的分子水平建模，所有这些都对未来燃料电池技术的可能应用具有相当大的兴趣。一般来说，质子传导由于其固有的复杂性，对当前的计算方法提出了巨大的挑战。将开发一种新的方法，通过将最先进的模拟技术与分子相互作用的准确描述相结合，来应对这一挑战。由此产生的计算方法将集成到Amber中，Amber是最流行的分子动力学模拟软件包之一。研究生和本科生以及博士后将参与研究，并将获得理论，物理和材料化学的坚实基础。拟议项目的外展部分还包括PI继续参与研究学者计划，该计划为来自全国各地的高中生提供在加州大学圣地亚哥分校进行暑期研究的机会。

TECHNICAL SUMMARYThe Chemistry Division and the Division of Materials Research contribute funds to this award. It supports theoretical research and education with the objective to model proton conduction in metal-organic frameworks through the development and application of a novel simulation methodology. Proton conduction in solids and porous materials is a process of fundamental importance for fuel cell technologies. Much of current research on fuel cells focuses on proton exchange membranes where the electrolytes are Nafion or some other sulfonated polymers. Since high proton conductivity is only obtained at high levels of hydration, the maximum operation temperature of current fuel cells is limited by the condensation point of water. Metal-organic frameworks are conceptually different separator materials that can transport protons at high temperatures and in low-humidity environments. One of the main advantages of metal-organic frameworks is the possibility to modify the inner surface of their pores with respect to hydrophilicity and acidity via suitable organic ligands, which can be used to control proton conduction at the molecular level. This research project focuses on the molecular-level modeling of proton conduction in several chemically and structurally different metal-organic frameworks, all of which are of considerable interest for possible applications in fuel cell technologies. The specific foci are: 1) Proton conduction via water molecules adsorbed in the nanochannels, 2) Proton conduction via nitrogen-containing molecules adsorbed in the nanochannels, 3) Proton conduction in functionalized metal-organic frameworks. Proton conduction presents a challenge for current computational methodologies due to the dynamically changing bonding topologies of numerous molecular structures and complexity of the surrounding chemical environment. A precise characterization of proton conduction requires a physically complete representation of the underlying many-body interactions as well as an extensive sampling of the relevant phase space. The rigorous combination of these two components ultimately leads to the correct description of the free-energy landscape that governs the thermodynamics and kinetics of proton transport. A novel computational approach will be developed that meets this challenge by combining an ab initio-based representation of proton hopping with an accurate description of the framework-framework and framework-guests interactions. This will provide molecular-level insights into the mechanisms that govern proton transport in metal-organic frameworks, which is the first, necessary step toward the rational design of new conducting metal-organic framework structures that can function at higher temperatures and lower relative humidity for application in next generation fuel cells. Graduate and undergraduate students as well as postdoctoral fellows will be involved in the research and will acquire a solid foundation in theoretical, physical, and materials chemistry. The computational approach developed within this project will be integrated in Amber, a popular molecular dynamics simulation package. The outreach component also includes the PI's continuing involvement with the Research Scholars Program, which provides high-school students from across the country with the opportunity to carry out summer research at UC San Diego.NONTECHNICAL SUMMARYThe Chemistry Division and the Division of Materials Research contribute funds to this award. It supports an integrated theoretical and computational research and education program related to fuel cell technologies as alternative energy sources. The increasing energy demands and associated effects on the environment pose strict constraints on future use of natural resources such as oil and gas. Considerable effort has recently been devoted to the development of alternative energy sources such as fuel cells that convert chemical energy into directly usable forms. For example, hydrogen fuel cells exploit a fundamental chemical reaction in which the electrons are first drawn from hydrogen molecules to produce protons at the anode, and then are transferred to the cathode through an external circuit that produces direct current. At the same time, the protons are transported across a permeable membrane from the anode to the cathode where they are reunited with the electrons to form molecular hydrogen that subsequently reacts with oxygen to form water. The net result is thus the conversion of chemical energy into electrical energy. Since the overall products are water and heat, hydrogen fuel cells are clean technologies with regard to environmental issues. One of the reasons why fuel cells have not yet found wider application is related to their efficiency, which strongly depends on the ability of protons to quickly travel across the membrane from the anode to the cathode. The particular nature of the membranes that are currently used represent the major obstacle to the development of more efficient fuel cells. The primary goal of this project is to use computer simulation to characterize the molecular mechanisms that determine proton conduction in a new class of materials known as metal-organic frameworks. Metal-organic frameworks contain organic molecules that act as bridges between inorganic clusters to form highly porous three-dimensional structures. Due to the presence of microscopic pores and channels, metal-organic frameworks can thus be used as effective separators in fuel cell technologies in which protons can be shuttled from the anode to the cathode through intervening carrier molecules or through the framework itself.The proposed project focuses on the molecular-level modeling of proton conduction in several chemically and structurally different metal-organic frameworks, all of which are of considerable interest for possible applications in future fuel cell technologies. In general terms, proton conduction presents an enormous challenge for current computational approaches due to its intrinsic complexity. A new methodology will be developed that meets this challenge by combining state-of-the-art simulation techniques with accurate descriptions of the molecular interactions. The resulting computational approach will be integrated into Amber, which is one of the most popular software packages for molecular dynamics simulations. Graduate and undergraduate students as well as postdoctoral fellows will be involved in the research and will acquire a solid foundation in theoretical, physical, and materials chemistry. The outreach component of the proposed project also includes the PI continuing involvement with the Research Scholars Program, which provides high-school students from across the country with the opportunity to carry out summer research at UC San Diego.