International Collaboration in Chemistry: A Combined Computational and Spectroscopic Study of Structure and Charge Transfer Dynamics of Ionic Liquids in Heterogeneous Environments

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Hyung Kim of Carnegie Mellon University is supported by the Chemical Structure, Dynamics and Mechanisms program of the Division of Chemistry through the International Collaboration in Chemistry initiative to carry out computational and spectroscopic study of structure and dynamics of ionic liquids in heterogeneous environments in collaboration with experimental groups at University of Aberdeen, UK headed by Dr. Johannes Kiefer and Prof. James Anderson. The research component of the UK collaborators will be funded through EPSRC. The US investigator, Professor Kim, will perform molecular dynamics (MD) simulations of room-temperature ionic liquids (RTILs) based on imidazolium cations in metal organic frameworks (MOFs) and in carbonaneous environments, including carbon black, carbon nanotubes and graphenes, and analyze RTIL structures and dynamics with special attention paid to the environmental effect. Using the equilibrium structure thus obtained, quantum chemistry calculations will be performed in the QM/MM (quantum mechanics/molecular mechanics) framework to determine RTIL vibrational spectra. Reorganization of electron density of RTIL ions, in particular, imidazolium cations, will be analyzed and heterogeneous charge transfer at the interface with graphitic materials will be investigated. An empirical valence-bond description for electron transfer between cations and graphene surface will be constructed and incorporated into MD simulations. Several different anionic species, such as bis(trifluoromethylsulfonyl)imide and bis(fluorosulfonyl)imide, will be considered to understand how redox chemistry of imidazolium cations could be modulated by anions. Detailed comparison of computational results will be made with the experimental results that will be obtained via, among other methods, Fourier-transform infrared spectroscopy (FTIR), x-ray absorption spectroscopy (XAS) and inelastic neutron scattering (INS) by the UK collaborators. Experimental results for RTILs in MOFs with well-defined pore size and shape will be used to calibrate computational results and fine-tune force field parameters. Later, RTIL systems will be extended to mixtures with organic solvents and the influence of co-solvents on RTIL structure, dynamics and charge transfer at the interface with carbon-based materials will be studied.Room-temperature ionic liquids (RTILs) have many unique properties that make them promising solvents for green technology: they are non-volatile, non-flammable, chemically inert and thermally stable. RTILs are also promising as components of systems for energy conversion and storage because of their high ion conductivity and large electrochemical window. These electrochemical properties also make RTILs potentially useful in catalysis and other industrial processes. Prof. Kim's research helps to provide detailed microscopic insight into the structure and properties of RTILs by studying their interactions with interfaces similar to those used in such applications using a combination of theory/computation and experiment/spectroscopy. As such, the research will have long-range impacts on both the fundamental understanding of RTIL interfacial processes and their many potential applications. Key results of the research will be incorporated into ChemCollective, a digital library of educational materials for introductory chemistry courses at both the college and high school level, developed at Carnegie Mellon University, to disseminate the results to a broad audience, including high school students, undergraduates and their instructors.