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.

技术摘要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，旨在通过开发和应用新型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对于燃料电池技术来说是一个至关重要的过程。目前燃料电池的大部分研究都集中在质子交换膜上，其中电解质是 Nafion 或一些其他磺化聚合物。由于高质子电导率只有在高水合水平下才能获得，因此当前燃料电池的最高工作温度受到水凝点的限制。金属有机框架在概念上是不同的分隔材料，可以在高温和低湿度环境下传输质子。金属有机框架的主要优点之一是可以通过合适的有机配体改变其孔内表面的亲水性和酸性，可用于在分子水平上控制质子传导。该研究项目重点关注几种化学和结构不同的金属有机框架中质子传导的分子水平建模，所有这些对于燃料电池技术中的可能应用都具有相当大的兴趣。具体焦点是：1）通过纳米通道中吸附的水分子进行质子传导，2）通过纳米通道中吸附的含氮分子进行质子传导，3）功能化金属有机框架中的质子传导。由于众多分子结构的动态变化的键合拓扑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进行物理完整的表示以及对相关相空间的广泛采样。这两个组成部分的严格组合最终导致对控制质子传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，通过将质子跳跃的从头算表示与框架-框架和框架-客体相互作用的准确描述相结合来应对这一挑战。这将为控制金属有机框架中质子传输的机制提供分子水平的见解，这是合理设计新型导电金属有机框架结构的第一步，也是必要的一步，该结构可以在更高的温度和更低的相对湿度下发挥作用，以应用于下一代燃料电池。研究生、本科生以及博士后将参与这项研究，并在理论、物理和材料化学方面打下坚实的基础。该项目中开发的计算方法将集成到流行的分子动力学模拟软件包 Amber 中。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夏季研究的机会。非技术摘要化学系和材料研究系为该奖项提供资金。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及教育计划。不断增长的能源需求及其对环境的影响对石油和天然气等自然资源的未来使用提出了严格的限制。最近，人们投入了大量精力来开发替代能源，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，其中电子首先从氢分子中汲取，在阳极产生质子，然后通过产生直流电的外部电路转移到阴极。同时，质子穿过渗透膜从阳极传输到阴极，在阴极与电子重新结合形成氢分子，随后与氧反应形成水。最终结果是将化学能转化为电能。由于氢燃料电池的总体产物是水和热，因此就环境问题而言，氢燃料电池是清洁技术。燃料电池尚未得到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快速穿过膜从阳极到达阴极的能力。目前使用的膜的特殊性质是开发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决定金属有机框架新型材料中质子传导的分子机制。金属有机框架含有有机分子，它们充当无机团簇之间的桥梁，形成高度多孔的三维结构。由于存在微观孔隙和通道，金属有机框架可以用作燃料电池技术中的有效分离器，其中质子可以通过介入的载体分子或通过框架本身从阳极穿梭到阴极。该项目重点关注几种化学和结构不同的金属有机框架中质子传导的分子水平建模，所有这些都引起了相当大的兴趣 未来燃料电池技术的可能应用。一般来说，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、本科生以及博士后将参与这项研究，并在理论、物理和材料化学方面打下坚实的基础。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夏季研究的机会。