The 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 SUMMARY
The 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.
