The Interfacial Processes Group studies the structures and reactions at solid-liquid interfaces. These studies are performed with a combination of advanced synchrotron-based tools along with traditional interfacial probes (e.g., scanning probe microscopy, electrochemistry, etc.). We emphasize two general areas of study:
- Interfacial Geochemistry: Reactions at mineral-water interfaces (e.g., adsorption, growth, and dissolution) effectively control the fate and transport of elements in Earth’s near-surface environment, including nutrients necessary for life as well as toxins (e.g., held in geological repositories). Our research is aimed at achieving a better understanding of these interfacial reactions through direct observation of structures and processes at the molecular level. This information can be used as the basis for making informed assessments concerning the performance of repositories for carbon dioxide sequestration and high-level nuclear waste storage.
- Energy Storage Systems: Reactions at electrode-electrolyte interface are critical to the performance of energy storage systems, such as lithium ion batteries and super capacitor systems, especially due to the high electric fields and materials stresses that are present. In the case of lithium ion batteries, for example, interfacial reactions lead to the formation of the “solid-electrolyte interface” (SEI) that is critical to operation of the battery, by preventing the spontaneous breakdown of the battery materials (e.g., fire), but also can impair battery lifetime and cyclability. Our goal is to understand the structures and reactions in these systems through direct in-situ observations.
Recent Research Results
Geochemistry: Recent studies have explored the molecular structure of mineral surfaces, the ordering of fluids adjacent to these surfaces (e.g., interfacial hydration layers), and the distribution of adsorbed ions at charged mineral surfaces (e.g., electrical double-layer structure), as well as dynamical processes such as dissolution and heterogeneous growth processes through real-time observations. These observations lead to new insights into the specific reaction mechanisms at mineral/fluid interfaces, define the kinetics and reaction mechanisms at the atomic scale in key mineral/fluid systems, and provide critical tests of our understanding of mineral/water reactivity though comparison with predictions of high-level theoretical studies.
Energy Storage: Recent advances have provided new insights into the structure and spectroscopy of lithiated materials, as well as in-situ and real-time observations of lithiation processes of at a battery's electrode-electrolyte interface (CEES Center). Other studies have explored the structure of the graphene-water and graphene-RTIL interface through direct measurements of X-ray reflectivity (FIRST Center).
Technical Advances and Details
The ability to make robust observations of these processes relies on the application and development of advanced synchrotron-based interfacial x-ray tools for in-situ studies of solid-liquid interfaces. These approaches take advantage of the unique characteristics of synchrotron radiation at the Advanced Photon Source (APS), including temporal and spatial resolution afforded by the high APS beam brilliance and the tunability of the x-ray photon energy that facilitates spectroscopic sensitivities, leading to fundamentally new types of in situ experiments.
Projects primarily use high (<1 Å) resolution X-ray scattering techniques, including surface x-ray scattering (e.g., X-ray reflectivity, XR), resonant anomalous x-ray reflectivity (RAXR), X-ray standing waves (XSW), and x-ray reflection interface microscopy (XRIM).
The relatively high complexity of these solid-liquid interfaces has also led to the development and extension of various model-independent data analysis techniques, including the ability to image directly: element-specific sub-profiles (e.g., from phase-sensitive Bragg-XSW, total-external reflection (TER)-XSW data, and RAXR data) and interfacial density profiles from XR data (e.g., using error correction algorithms).
Research Partners and Funding
The Interfacial Geochemistry work has ongoing collaborations with scientists at many organizations, including the University of Illinois at Chicago, Northwestern University, the Illinois State Water Survey, and Oak Ridge National Laboratory. This research is funded by the Geoscience Research program of the Department of Energy’s Office of Basic Energy Sciences.
The work on lithium ion battery materials is performed within the context of the Center for Electrical Energy Storage, which consists of researchers from Argonne, Northwestern University and the University of Illinois at Urbana-Champaign. This research is funded by the Department of Energy’s Office of Basic Energy Sciences.
The work on graphene-aqueous electrolyte systems is performed within the context of the Fluid Interfaces, Structure and Transport (FIRST) Center, which is led by Oak Ridge National Laboratory, along with Argonne, Drexel University, Vanderbilt University and others. This research is funded by the Department of Energy’s Office of Basic Energy Sciences.
- Publications since 1999 (pdf)