Computer Modeling of Proton Conduction in Metal-Organic Frameworks

金属有机框架中质子传导的计算机建模

• 批准号: 1305101
• 负责人: Francesco Paesani
• 金额: $ 35.1万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1305101&HistoricalAwards=false
• 关键词: Computer; Modeling; Proton; Conduction; Metal

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.

技术总结化学部和材料研究部为该奖项贡献了资金。它支持理论研究和教育，目的是通过开发和应用新颖的仿真方法来对金属有机框架中的质子传导进行建模。固体和多孔材料中的质子传导是对燃料电池技术的基本重要性。当前对燃料电池的许多研究都集中在电解质是Nafion或其他一些磺化聚合物的质子交换膜上。由于高质子电导率仅在高水平的水合下获得，因此电流燃料电池的最高操作温度受水的冷凝点的限制。金属有机框架在概念上是不同的分离材料，可以在高温和低湿度环境中运输质子。金属有机框架的主要优点之一是通过合适的有机配体来修改其孔内表面相对于亲水性和酸度的内部表面，该配体可用于控制分子水平的质子传导。该研究项目着重于几种化学和结构上不同的金属有机框架中质子传导的分子级建模，所有这些框架对于燃料电池技术中的可能应用引起了极大的兴趣。特定灶是：1）通过吸附在纳米通道中的水分子传导的质子传导，2）通过含氮分子吸附的质子传导，吸附在纳米渠道中的质子，3）在功能化的金属有机框架中质子传导。由于众多分子结构的动态变化粘结拓扑以及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基本多体相互作用的物理完整表示以及相关相位空间的广泛采样。这两个组成部分的严格组合最终导致对控制质子运输的热力学和动力学的自由能景观的正确描述。将开发一种新颖的计算方法，通过将基于质量的质子跳跃的表述与对框架框架和框架 - 环境相互作用的准确描述相结合，以应对这一挑战。这将提供分子级别的见解，以介绍在金属有机框架中质子转运的机制，这是朝着合理设计的新导电金属有机框架结构的合理设计的第一步，该结构可以在较高的温度下起作用，并且在下一代燃料电池中应用较低的相对湿度。研究生和本科生以及博士后研究员将参与研究，并将在理论，物理和材料化学方面获得坚实的基础。该项目中开发的计算方法将集成在流行的分子动力学仿真软件包中。外展部分还包括PI的持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了在圣地亚哥分校进行夏季研究的机会。综合技术摘要化学部和材料研究部为该奖项贡献了资金。它支持与燃料电池技术作为替代能源有关的综合理论和计算研究和教育计划。能源不断提高的需求和对环境的相关影响对石油和天然气等自然资源的未来使用构成了严格的限制。最近，已大量努力致力于开发替代能源的诸如将化学能量转化为直接可用形式的燃料电池。例如，氢燃料电池利用了基本化学反应，其中首先从氢分子中抽取电子以在阳极下产生质子，然后通过产生直流电流的外部电路转移到阴极。同时，将质子从阳极到阴极的渗透膜转运到与电子团聚，形成分子氢，随后与氧气反应形成水。因此，最终结果是化学能转化为电能。由于整体产品是水和热量，因此氢燃料电池是关于环境问题的干净技术。燃料电池尚未发现更广泛应用的原因之一与其效率有关，这在很大程度上取决于质子在从阳极到阴极迅速穿越膜的能力。当前使用的膜的特殊性质代表了开发更有效的燃料电池的主要障碍。该项目的主要目的是使用计算机模拟来表征确定一种新的称为金属有机框架的新材料中质子传导的分子机制。金属有机框架包含有机分子，它们充当无机簇之间的桥梁，形成高度多孔的三维结构。由于存在微观孔和通道，因此可以将金属有机框架用作燃料电池技术中的有效分离器，在该技术中，可以通过中间的载载分子或通过框架本身将质子从阳极到阴极的质子或通过框架本身。用于未来燃料电池技术中的可能应用。总的来说，质子传导由于其内在的复杂性，对当前的计算方法提出了巨大的挑战。将开发一种新方法，通过将最新的仿真技术与对分子相互作用的准确描述相结合，以应对这一挑战。所得的计算方法将集成到琥珀中，这是用于分子动力学模拟的最流行的软件包之一。研究生和本科生以及博士后研究员将参与研究，并将在理论，物理和材料化学方面获得坚实的基础。拟议项目的外展部分还包括PI持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了在圣地亚哥加州大学加州大学加州大学的夏季研究的机会。