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Title: Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition

Abstract

The energy density of an electric double layer (EDL) capacitor, a type of supercapacitor, depends on the ion distribution within the micropores of electrodes that are typically made of amorphous carbon. By using coarse-grained models and the classical density functional theory, we investigate the distributions of ionic species among different idealized nanopores in contact with an asymmetric ionic liquid mixture and the effects of the bulk electrolyte composition on capacitive energy storage. We find that a charged pore is always small-ion selective, provided all ions have the same valence and similar non-electrostatic interactions. While small ions enhance both the EDL capacitance and the accessibility of micropores, an ionic mixture containing ions of different sizes may yield a capacitance higher than those corresponding to pure ionic liquids. Furthermore, the increased capacitance may be attributed to more efficient ion packing near the charged surface. At certain conditions, the improvement is on a par with the anomalous capacitance rise for pure ionic liquids in electrodes with ultranarrow pores.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [1]
  1. Univ. of California, Riverside, CA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Brigham Young Univ., Provo, UT (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1557520
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Molecular Liquids
Additional Journal Information:
Journal Volume: 270; Journal Issue: C; Journal ID: ISSN 0167-7322
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Porous electrodes; Capacitance; Ionic-liquid mixtures; EDL structure; Ion selectivity; Classical density functional theory

Citation Formats

Neal, Justin N., Wesolowski, David J., Henderson, Douglas, and Wu, Jianzhong. Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition. United States: N. p., 2017. Web. doi:10.1016/j.molliq.2017.10.128.
Neal, Justin N., Wesolowski, David J., Henderson, Douglas, & Wu, Jianzhong. Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition. United States. doi:10.1016/j.molliq.2017.10.128.
Neal, Justin N., Wesolowski, David J., Henderson, Douglas, and Wu, Jianzhong. Fri . "Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition". United States. doi:10.1016/j.molliq.2017.10.128. https://www.osti.gov/servlets/purl/1557520.
@article{osti_1557520,
title = {Electric double layer capacitance for ionic liquids in nanoporous electrodes: Effects of pore size and ion composition},
author = {Neal, Justin N. and Wesolowski, David J. and Henderson, Douglas and Wu, Jianzhong},
abstractNote = {The energy density of an electric double layer (EDL) capacitor, a type of supercapacitor, depends on the ion distribution within the micropores of electrodes that are typically made of amorphous carbon. By using coarse-grained models and the classical density functional theory, we investigate the distributions of ionic species among different idealized nanopores in contact with an asymmetric ionic liquid mixture and the effects of the bulk electrolyte composition on capacitive energy storage. We find that a charged pore is always small-ion selective, provided all ions have the same valence and similar non-electrostatic interactions. While small ions enhance both the EDL capacitance and the accessibility of micropores, an ionic mixture containing ions of different sizes may yield a capacitance higher than those corresponding to pure ionic liquids. Furthermore, the increased capacitance may be attributed to more efficient ion packing near the charged surface. At certain conditions, the improvement is on a par with the anomalous capacitance rise for pure ionic liquids in electrodes with ultranarrow pores.},
doi = {10.1016/j.molliq.2017.10.128},
journal = {Journal of Molecular Liquids},
number = C,
volume = 270,
place = {United States},
year = {2017},
month = {11}
}

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