Ion and Solvent Dynamics in Charged 2D Clay Nanoslits with Unprecedented Ångström-Precise Slit Height Control

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Stevenson, Max ; Pappler, Sandra ; Kanzler, Leonie ; Nisar, Aqsa ; Parambath, Jepsinraj Kakkuzhiyulla ; Rosenstihl, Markus ; Lebeda, Flora ; Weiß, Sebastian ; Papastavrou, Georg ; Vogel, Michael ; Senker, Jürgen ; Breu, Josef:
Ion and Solvent Dynamics in Charged 2D Clay Nanoslits with Unprecedented Ångström-Precise Slit Height Control.
In: Advanced Functional Materials. (27 August 2025) . - e15706.
ISSN 1616-3028
DOI der Verlagsversion: https://doi.org/10.1002/adfm.202515706

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Abstract

Abstract Nanoconfinement by layered silicates has been claimed to deliver superionic conductivity as needed for many electrochemical applications. Unraveling governing principles of solvent and ion dynamics within charged 2D nanochannels requires Å-precise slit height control. This work addresses existing experimental limitations utilizing synthetic fluorohectorite, known for its superb homogeneous charge distribution, high aspect ratio (> 20,000), and spontaneous delamination by 1D-dissolution. This triad of properties enables an Å-precise slit height control of monodomain Bragg stack membranes over a wide slit height range (5–100 Å) while offering a variable and high surface charge (0.17–0.24 C m−2). A concerted characterization applying electrochemical impedance spectroscopy (EIS), colloidal-probe atomic force microscopy (CP-AFM), pulsed- and static-field gradient nuclear magnetic resonance (PFG- and SFG-NMR), assisted by molecular dynamics (MD) simulations, revealed in-depth insights: The maximum conductivity (0.2 S m−1) is observed at a confinement of 15.1 Å, where aside of the two Helmholtz planes (HP) attached to the confinement walls a diffuse layer (DL) exists. Independent of the surface charge, the vast majority of Li+ is strongly bound by electrostatics and hydrogen bonding of the first hydration shell to the anionic walls. Regardless of the slit height and electrolyte concentration, conductivity is governed by the Li+ balancing the surface charge.