Atomistic Insights into the Layered Microstructure and Time Dependent Stability of BMIMPF6 Confined within the Meso-Slit of Carbon

ZY Dai and YJ You and YD Zhu and SS Wang and W Zhu and XH Lu, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 6857-6869 (2019).

DOI: 10.1021/acs.jpcb.9b02682

Clarifying the microstructures and time-dependent stability of ionic liquids (ILs) within the confinement of the meso-slit of carbon is the first step to understand the intrinsic synergy effect between ILs and a promising mesoporous carbon electrode. In this work, we adopted molecular dynamics to systematically investigate the behavior of BMIMPF6 in the 2.8 nm-wide meso-slit of carbon. The confined ILs formed a pronounced layered spatial distribution and can be divided into three distinct regions, namely, corn-, sub-, and cen-layer, according to valley coordinates in the number density profiles. In the corn-layer region, the imidazolium rings of ILs possess two dominant orientations, namely, "parallel" and "tilted standing". The rotation ability of all the ions is highly restrained. In the sub-layer and cen-layer regions, a part of the BMIM imidazolium ring has a preferred "tilted standing" orientation. The BMIM cations are still in a rotational restrain state and show a preferred rotation motion along the x-y plane. The hydrogen bond between BMIM cations and PF6 anions play a crucial role in determining the confined multilayered spatial distribution and distinctive orientation properties of ILs.

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