Understanding and controlling reactions at electrode-electrolyte interfaces remains a major challenging in electrochemical energy storage and conversion, due to the complexity of these systems (e.g., for both the solids and electrolytes) and significant structural and chemical changes that can take place as a function of applied potentials. I will present recent work in which we seek to isolate and understand the role of interfacial reactivity in these systems through in-situ, real-time, observations of electrochemically driven reactions at well-defined model electrode-electrolyte interfaces using X-ray reflectivity. I will discuss two distinct types of electrochemical energy systems: 1) lithium ion battery chemistries in which energy is stored upon lithium ion incorporation into electrodes (e.g., insertion reactions in LixMn2O4 and conversion reactions in NiO) using well-defined thin-film and multilayer electrode structures; and 2) the electrochemical reduction of CO2 at bismuth electrolyte interfaces in ionic liquid based electrolytes solutions where we observe dramatic changes in the electrode structure prior to onset of CO2 reduction. These observations provide new insights into the complex reaction pathways of these materials through in operando observations.
Acknowledgment: This work was supported as part of the Center for Electrochemical Energy Science (CEES) and the Fluid Interface Reactivity Structure and Transport Center (FIRST), which are Energy Frontier Research Centers funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The work was done in collaboration with J. Medina-Ramos, T. Fister, S. S. Lee (ANL), X. Chen, G. Evmenenko, M. Bedzyk (Northwestern), D. Lutterman R. Sacci (ORNL), A. van Duin (Penn State), M. Neurock (U. Minnesota) and J. Rosenthal (U. Delaware).