Lawrence Livermore researchers couple x-ray spectroscopy with modeling to understand interfacial phenomena in energy materials.
Energy materials often operate in chemical, temporal, or spatial regimes that are challenging to isolate and characterize experimentally. In particular, surfaces and interfaces that are critical to the lifetime, efficiency, and performance of these materials can be either buried in the device architecture, in contact with liquids and gases, or electrically connected to an applied bias.
X-ray spectroscopies have emerged as a powerful characterization strategy for interrogating these surfaces and interfaces. Synchrotron sources available at DOE user facilities, in addition to a suite of lab-based surface science techniques at LLNL (such as x-ray photoelectron spectroscopy [XPS]), have further enabled methods for in situ/in operando measurements, such as x-ray absorption spectroscopy (XAS), with improved chemical, spatial, and/or temporal sensitivity suitable to measuring fundamental energy materials phenomena. We used in operando XAS to investigate potential-induced changes in the electronic structure of carbon electrodes within an operating supercapacitor.
Within our team at LLNL, x-ray spectroscopies are tightly integrated with modeling efforts to predict spectroscopic signatures, interpret experimental results, and refine theory. Ab initio spectroscopy simulations, based on density functional theory and the excited core-hole approximation, produce virtual x-ray spectra from model systems that can be directly compared with the in situ/operando data to glean unique insights from often highly complex spectra. This highly iterative, robust coupling of advanced characterization and state-of-the-art simulation is a successful approach to understanding interfacial phenomena in energy materials.
Publications
M. Bagge-Hansen, B.C. Wood, T. Ogitsu, T.M. Willey, I.C. Tran, A. Wittstock, M.M. Biener, M.D. Merrill, M.A. Worsley, M. Otani, C.H. Chuang, D. Prendergast, J.H. Guo, T.F. Baumann, T. van Buuren, J. Biener, J.R.I. Lee, Supercapacitors: Potential‐Induced Electronic Structure Changes in Supercapacitor Electrodes Observed by In Operando Soft X‐Ray Spectroscopy, Adv. Mater. 27, 1512 (2015). Featured on cover: March 2015
