Project Overview (Summary Slides)
Scientific Objectives: The unique properties of the FSI emerge from a complex interplay of short- and long-range forces and reactions among the molecular fluid components, solutes and substrates. Potential gradients (chemical, electrical, etc.) can be highly non-linear at the angstrom to nanometer scale. The finite size, shape, directional bonding, charge distribution and polarizability of solvent and solute fluid components are convoluted with their ability to reorient, ‘unmix’ and react with one another and the substrate. The truncated solid surface exposes under-bonded atoms that drive dynamic interactions with the adjacent fluid by local bond relaxation, charge redistribution, dissolution, precipitation, sorption and porosity development/destruction. Heretofore, interfaces have been described using hypothetical concepts of interfacial structure, such as the century-old Gouy-Chapman-Stern-Helmholtz models of the electrical double layer at the interface between charged surfaces and electrolyte solutions. Such models are commonly invoked to explain charging of batteries and capacitors and the distribution of ions and solvent molecules at catalytic interfaces, despite the fact that they have no molecular basis, and contain no dynamic information. We intend to replace such models with molecular-level quantitative models that realistically capture the structural, reactive and transport properties of energy-relevant interfaces, over the full range of time (femtoseconds to milliseconds and length (sub-angstrom to sub-micron) scales that encompass the unique, emergent properties of interfacial systems.
Research Strategies: Our strategy to overcoming these barriers is to take a hierarchical and highly-integrated approach, coupling unique experimental, chemical imaging and computational probes of FSI structures, reactions, and transport phenomena. This research is being pursued in three parallel and highly integrated thrusts that address increasing levels of FSI complexity. The primary focus of Thrust 1, is to develop experimentally-calibrated and validated molecular models of fluid (aqueous, polar organic, ionic liquid) interactions with charged and uncharged surfaces (carbons, metal oxides), mainly in a planar or unconfined geometry. This enables the application of advanced neutron, X-ray, NMR and nonlinear optical probes of interfacial structure and dynamics and facilitates coupling these atomic-nanoscale imaging results with multiscale computational models that capture the chemical realism of FSIs that will be studied in the other Thrusts. In Thrust 2, we are investigating how nanoscale confinement and surface functionalization influence solvent/solute transport at tailored carbon and metal oxide surfaces with unique control of interfacial geometry and electrolyte chemistry and structure. We are also investigating the effect of substrate chemical and textural evolution through time, such as is encountered during “Solid-Electrolyte Interphase” (SEI) formation at battery electrode surfaces. In Thrust 3, we are determining how the unique properities of interfacial fluids couple with reactive surface sites to control reaction pathways, selectivity, and energetics. We are focusing on proton-coupled electron transfer reactions in the electrocatalytic and photocatalytic redox reactions of CO2, O2 and water at carbon and oxide surfaces in contact with dense fluid phases.
Major Facilities: This research program is anchored in ORNL’s core strengths in chemical, materials, neutron, computational, and nanoscale sciences, which will ensure scientific excellence. We are taking advantage of the unique user facilties available at ORNL, including the Spallation Neutron Source (SNS) and High Flux Isotope Reactor, National Center for Computational Science , Center for Nanophase Materials Sciences , and the electron microscopies of the Shared Research Equipment User Facility , as well as the Advanced Photon Source at Argonne National Laboratory (ANL). The Center’s partner institutions (ANL, Drexel, Georgia State, Northwestern, Penn State and Vanderbilt Universities and the University of Virginia) complement and extend the scientific expertise and enhance educational outreach.
