Research ArticleNANOMATERIALS

Single-layer nanosheets with exceptionally high and anisotropic hydroxyl ion conductivity

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Science Advances  14 Apr 2017:
Vol. 3, no. 4, e1602629
DOI: 10.1126/sciadv.1602629
  • Fig. 1 LDH and its hydroxyl ion conduction.

    Schematic diagrams for (A) the structure of LDH platelet, its exfoliation into single-layer nanosheets, and ion-conducting scenarios; (B) the plausible Grotthuss mechanism responsible for hydroxyl ion conduction; and (C) the measurement of in-plane ion conductivities of LDH nanosheets on comb electrodes.

  • Fig. 2 Determination of conducting ion types.

    Electromotive forces of water vapor concentration cells using cation exchange membrane (Nafion 117, DuPont), AEM (AHA, ASTOM Co.), GO membrane, and Mg-Al (Co-Al) LDH nanosheet membranes as the electrolytes.

  • Fig. 3 Hydroxyl ion conduction of LDH nanosheets.

    (A) Atomic force microscopy (AFM) image of Mg-Al LDH nanosheets. Scanning electron microscopy (SEM) (B) and AFM (C) images of single-layer Mg-Al LDH nanosheets deposited on comb electrodes. (D) Representative Nyquist plots of impedance for single-layer Mg-Al LDH nanosheets on comb microelectrodes. The inset shows an enlarged view of the high-frequency section. (E) Temperature dependences of in-plane ionic conductivity for single-layer Mg-Al LDH nanosheets at different RHs.

  • Fig. 4 Hydroxyl ion conduction of LDH platelets.

    SEM images of (A) Co-Al-CO32− and (B) Co-Ni-Br LDH hexagonal platelets deposited on comb electrodes. The inset in (A) shows an AFM image of isolated Co-Al-CO32− LDH platelet on comb teeth. (C) Representative Nyquist plots of impedance for Co-Ni-Br LDH platelets on comb electrodes. The inset shows an enlarged view of the high-frequency section. (D) Temperature dependences of ionic conductivity for various kinds of LDH platelets at 80% RH.

  • Fig. 5 Comparisons of hydroxyl ion conductivity values.

    (A) Schematic diagrams for the measurements of hydroxyl ion conductivities in different directions for both LDH nanosheets and hexagonal lamellar platelets. (B) Summary and comparison of the measured values at 60°C and 80% RH.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602629/DC1

    Supplementary Materials and Methods

    fig. S1. SEM characterizations of as-synthesized and anion-exchanged LDHs.

    fig. S2. XRD characterizations of as-synthesized and anion-exchanged LDHs.

    fig. S3. AFM characterizations of LDH nanosheets with different sizes.

    fig. S4. Schematic drawings for nanosheets on comb electrodes.

    fig. S5. Impedance spectra of bare comb electrodes acquired at 30°C and 80% RH.

    fig. S6. SEM characterizations of LDH nanosheet multilayers.

    fig. S7. Hydroxyl ion conduction of LDH nanosheet multilayers.

    fig. S8. Hydroxyl ion conduction of multilayer assemblies composed of micro- and nano-sized LDH nanosheets.

    fig. S9. Temperature dependences of in-plane ionic conductivity for a representative sample of micro–Mg-Al LDH nanosheet multilayers deposited on comb electrodes during a large time interval of over half a year to show the long-term stability of exfoliated LDH nanosheets in terms of hydroxyl ion conduction.

    fig. S10. SEM characterizations of LDH nanosheet membranes.

    fig. S11. Cross-plane hydroxyl ion conduction of LDH nanosheets acquired with lamellar membranes.

    fig. S12. Isotope effect experiments.

    fig. S13. XRD patterns of Mg-Al and Co-Al LDH nanosheet multilayers.

    fig. S14. Representative Nyquist plots of impedance for pellets containing Co-Al-CO32− LDH platelets.

    fig. S15. Hydroxyl ion conduction of LDH platelet-based pellets.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • fig. S1. SEM characterizations of as-synthesized and anion-exchanged LDHs.
    • fig. S2. XRD characterizations of as-synthesized and anion-exchanged LDHs.
    • fig. S3. AFM characterizations of LDH nanosheets with different sizes.
    • fig. S4. Schematic drawings for nanosheets on comb electrodes.
    • fig. S5. Impedance spectra of bare comb electrodes acquired at 30°C and 80% RH.
    • fig. S6. SEM characterizations of LDH nanosheet multilayers.
    • fig. S7. Hydroxyl ion conduction of LDH nanosheet multilayers.
    • fig. S8. Hydroxyl ion conduction of multilayer assemblies composed of micro- and nano-sized LDH nanosheets.
    • fig. S9. Temperature dependences of in-plane ionic conductivity for a representative sample of micro–Mg-Al LDH nanosheet multilayers deposited on comb electrodes during a large time interval of over half a year to show the long-term stability of exfoliated LDH nanosheets in terms of hydroxyl ion conduction.
    • fig. S10. SEM characterizations of LDH nanosheet membranes.
    • fig. S11. Cross-plane hydroxyl ion conduction of LDH nanosheets acquired with lamellar membranes.
    • fig. S12. Isotope effect experiments.
    • fig. S13. XRD patterns of Mg-Al and Co-Al LDH nanosheet multilayers.
    • fig. S14. Representative Nyquist plots of impedance for pellets containing Co-Al-CO32− LDH platelets.
    • fig. S15. Hydroxyl ion conduction of LDH platelet-based pellets.

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