Ionic Liquid Structure and Dynamics at Charged Graphene Interface
Here, we use in situ real-time X-ray reflectivity integrated with fully atomistic molecular dynamics (MD) simulations to elucidate the interfacial ionic liquid structure and dynamics at epitaxial graphene electrode during cyclic voltammetry and potential steps . Our results suggest that the graphene-RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by MD simulations at various static potentials . The potential-driven transition between the two structures is characterized by an energy barrier (~0.15 eV) that is independent of temperature. The model nicely explains the coexistence of distinct anion and cation adsorbed structures and provides further insights to ultra-slow response of the interfacial structure to potential steps.
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* This effort was supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The research described here was done in collaboration with S. S. Lee, H. Zhou, P. Fenter (Argonne National Laboratory), G. Feng, S. Li, P. Cummings (Vanderbilt University), P. Fulvio, P. Zhang, S. Dai (Oak Ridge National Laboratory), J. McDonough, Y. Gogotsi (Drexel University)