Theinfluence of a hierarchical porous carbon network on the coherent dynamics of a nanoconfined room temperature ionic liquid: A neutron spin echo and atomistic simulation investigation

Journal Article · Wed Jan 01 00:00:00 EST 2014 · Carbon

DOI:https://doi.org/10.1016/j.carbon.2014.07.020· OSTI ID:1149778

Banuelos, Jose Leo ^[1]; Feng, Guang ^[1]; Fulvio, Pasquale F ^[1]; Li, Song ^[2]; Rother, Gernot ^[1]; Arend, Nikolas ^[1]; Faraone, Antonio ^[3]; Dai, Sheng ^[1]; Cummings, Peter T ^[1]; Wesolowski, David J ^[1]

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1. ORNL
2. Vanderbilt University, Nashville
3. National Institute of Standards and Technology (NIST)

The molecular-scale dynamic properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or [C4mim+ ][Tf2N ], confined in hierarchical microporous mesoporous carbon, were investigated using neutron spin echo (NSE) and molecular dynamics (MD) simulations. Both NSE and MD reveal pronounced slowing of the overall collective dynamics, including the presence of an immobilized fraction of RTIL at the pore wall, on the time scales of these approaches. A fraction of the dynamics, corresponding to RTIL inside 0.75 nm micropores located along the mesopore surfaces, are faster than those of RTIL in direct contact with the walls of 5.8 nm and 7.8 nm cylindrical mesopores. This behavior is ascribed to the near-surface confined-ion density fluctuations resulting from the ion ion and ion wall interactions between the micropores and mesopores as well as their confinement geometries. Strong micropore RTIL interactions result in less-coordinated RTIL within the micropores than in the bulk fluid. Increasing temperature from 296 K to 353 K reduces the immobilized RTIL fraction and results in nearly an order of magnitude increase in the RTIL dynamics. The observed interfacial phenomena underscore the importance of tailoring the surface properties of porous carbons to achieve desirable electrolyte dynamic behavior, since this impacts the performance in applications such as electrical energy storage devices.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1149778
• Journal Information: Carbon, Vol. 78; ISSN 0008-6223
• Country of Publication: United States
• Language: English