title: Electroneutrality breakdown and specific ion effects in nanoconfined aqueous electrolytes observed by NMR.
abstract: Ion distribution in aqueous electrolytes near the interface plays a critical role in electrochemical, biological and colloidal systems, and is expected to be particularly significant inside nanoconfined regions. Electroneutrality of the total charge inside nanoconfined regions is commonly assumed a priori in solving ion distribution of aqueous electrolytes nanoconfined by uncharged hydrophobic surfaces with no direct experimental validation. Here, we use a quantitative nuclear magnetic resonance approach to investigate the properties of aqueous electrolytes nanoconfined in graphitic-like nanoporous carbon. Substantial electroneutrality breakdown in nanoconfined regions and very asymmetric responses of cations and anions to the charging of nanoconfining surfaces are observed. The electroneutrality breakdown is shown to depend strongly on the propensity of anions towards the water-carbon interface and such ion-specific response follows, generally, the anion ranking of the Hofmeister series. The experimental observations are further supported by numerical evaluation using the generalized Poisson-Boltzmann equation.
authors.affiliation: Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, USA.
authors.forename: Zhi-Xiang
authors.identifier: 0000000227191025
authors.initials: ZX
authors.lastname: Luo
authors.affiliation: Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3216, USA.
authors.forename: Yun-Zhao
authors.initials: YZ
authors.lastname: Xing
authors.affiliation: Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3216, USA.
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, USA.
authors.forename: Alfred
authors.initials: A
authors.lastname: Kleinhammes
authors.affiliation: 1] Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, USA [2] Department of Applied Physical Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3216, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wu