Relationship between pore size and reversible and irreversible immobilization of ionic liquid electrolytes in porous carbon under applied electric potential

Journal Article · Tue Oct 04 00:00:00 EDT 2016 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4964130· OSTI ID:1328320

Mahurin, Shannon M. ^[1]; Mamontov, Eugene ^[2]; Thompson, Matthew W. ^[3]; Zhang, Pengfei ^[1]; Turner, C. Heath ^[4]; Cummings, Peter T. ^[3]; Dai, Sheng ^[5]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division
3. Vanderbilt Univ., Nashville, TN (United States). Dept. of Chemical and Biomolecular Engineering
4. Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Chemical and Biological Engineering
5. Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA; Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA

Transport of electrolytes in nanoporous carbon-based electrodes largely defines the function and performance of energy storage devices. Here, using molecular dynamics simulation and quasielastic neutron scattering, we investigate the microscopic dynamics of a prototypical ionic liquid electrolyte, [emim][Tf₂N], under applied electric potential in carbon materials with 6.7 nm and 1.5 nm pores. The simulations demonstrate the formation of dense layers of counter-ions near the charged surfaces, which is reversible when the polarity is reversed. In the experiment, the ions immobilized near the surface manifest themselves in the elastic scattering signal. The experimentally observed ion immobilization near the wall is fully reversible as a function of the applied electric potential in the 6.7 nm, but not in the 1.5 nm nanopores. In the latter case, remarkably, the first application of the electric potential leads to apparently irreversible immobilization of cations or anions, depending on the polarity, near the carbon pore walls. This unexpectedly demonstrates that in carbon electrode materials with the small pores, which are optimal for energy storage applications, the polarity of the electrical potential applied for the first time after the introduction of an ionic liquid electrolyte may define the decoration of the small pore walls with ions for prolonged periods of time and possibly for the lifetime of the electrode.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS); Energy Frontier Research Centers (EFRC) (United States). Fluid Interface Reactions, Structures and Transport Center (FIRST)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1328320
• Alternate ID(s): OSTI ID: 1420531
• Journal Information: Applied Physics Letters, Vol. 109, Issue 14; ISSN 0003-6951
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
25 ENERGY STORAGE
carbon
electrolytes
molecular dynamic