title: Dehydration of Ions in Voltage-Gated Carbon Nanopores Observed by in Situ NMR.
abstract: Ion transport through nanochannels is of fundamental importance in voltage-gated protein ion channels and energy storage devices. Direct microscopic observations are critical for understanding the intricacy of ionic processes in nanoconfinement. Here we report an in situ nuclear magnetic resonance study of ion hydration in voltage-gated carbon nanopores. Nucleus-independent chemical shift was employed to monitor the ionic processes of NaF aqueous electrolyte in nanopores of carbon supercapacitors. The state of ion hydration was revealed by the chemical shift, which is sensitive to the hydration number. A large energy barrier was observed for ions to enter nanopores smaller than the hydrated ion size. Increasing the gating voltage above 0.4 V overcomes this barrier and brings F(-) into the nanopores without dehydration. Partial dehydration of F(-) occurs only at gating voltage above 0.7 V. No dehydration was observed for Na(+) cations, in agreement with their strong ion hydration.
authors.affiliation: Department of Physics and Astronomy, University of North Carolina , Chapel Hill, North Carolina 27599-3255, United States.
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Luo
authors.affiliation: Department of Applied Physical Sciences, University of North Carolina , Chapel Hill, North Carolina 27599-3287, United States.
authors.forename: Yun-Zhao
authors.initials: YZ
authors.lastname: Xing
authors.affiliation: Research Computing Center, University of North Carolina , Chapel Hill, North Carolina 27599-3420, United States.
authors.forename: Shubin
authors.initials: S
authors.lastname: Liu
authors.affiliation: Department of Applied Physical Sciences, University of North Carolina , Chapel Hill, North Carolina 27599-3287, United States.
authors.forename: Yan-Chun
authors.initials: YC
authors.lastname: Ling
authors.affiliation: Department of Physics and Astronomy, University of North Carolina , Chapel Hill, North Carolina 27599-3255, United States.
authors.forename: Alfred
authors.initials: A
authors.lastname: Kleinhammes
authors.affiliation: Department of Physics and Astronomy, University of North Carolina , Chapel Hill, North Carolina 27599-3255, United States.|Department of Applied Physical Sciences, University of North Carolina , Chapel Hill, North Carolina 27599-3287, United States.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wu
keywords: NICS; carbon nanopores; nanoconfinement; supercapacitor; voltage-gated