Molecular Simulation of Metal-Ionic Liquid Interfaces

Surface interactions between metals and room temperature ionic liquids (RTILs) give rise to promising applications in catalysis, tribology, electrochemical deposition, and energy storage. Despite this, nanoscale features of the electric double layer (EDL) are poorly understood for more than a small number of metals. Here, we use a combination of molecular dynamics (MD) simulation, atomic force microscopy (AFM), and neutron reflectometry (NR) to study the structural ordering of ionic liquids at the interface of metal surfaces. Recent advances in AFM and NR have enabled the detection of ion layering at the EDL and structural responses to applied electrical potential. These experimental probes enable comparison to ion density profiles derived from MD. We initially consider the RTIL EMIM-Tf2N on a molybdenum surface. Due to a lack of appropriately generalizable force fields for a pure Mo surface, we parameterized Lennard-Jones interactions using contact angle experiments as target data. The derived fluid-solid interactions are used to explore the structure and orientation of RTIL molecules at the metal interface. Systems with and without applied electrical potentials are explored. The generalizability of this method to other surfaces, including bismuth, tin, and carbon, is explored.