Complex capacitance scaling in ionic liquids-filled nanopores

Peng Wu, Jingsong Huang, Vincent Meunier, Bobby G. Sumpter, Rui Qiao

Research output: Contribution to journalArticlepeer-review

181 Scopus citations

Abstract

Recent experiments have shown that the capacitance of subnanometer pores increases anomalously as the pore width decreases, thereby opening a new avenue for developing supercapacitors with enhanced energy density. However, this behavior is still subject to some controversy since its physical origins are not well understood. Using atomistic simulations, we show that the capacitance of slit-shaped nanopores in contact with room-temperature ionic liquids exhibits a U-shaped scaling behavior in pores with widths from 0.75 to 1.26 nm. The left branch of the capacitance scaling curve directly corresponds to the anomalous capacitance increase and thus reproduces the experimental observations. The right branch of the curve indirectly agrees with experimental findings that so far have received little attention. The overall U-shaped scaling behavior provides insights on the origins of the difficulty in experimentally observing the pore-width-dependent capacitance. We establish a theoretical framework for understanding the capacitance of electrical double layers in nanopores and provide mechanistic details into the origins of the observed scaling behavior. The framework highlights the critical role of "ion solvation" in controlling pore capacitance and the importance of choosing anion/cation couples carefully for optimal energy storage in a given pore system.

Original languageEnglish (US)
Pages (from-to)9044-9051
Number of pages8
JournalACS nano
Volume5
Issue number11
DOIs
StatePublished - Nov 22 2011

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy

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