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Proton conduction in alkali metal ion-exchanged porous ionic crystals

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Abstract

Proton conduction in alkali metal ion-exchanged porous ionic crystals A2[Cr3O(OOCH)6(etpy)3]2[α-SiW12O40nH2O [I-A+] (A = Li, Na, K, Cs, etpy = 4-ethylpyridine) is investigated. Single crystal and powder X-ray diffraction measurements show that I-A+ possesses analogous one-dimensional channels where alkali metal ions (A+) and water of crystallization exist. Impedance spectroscopy and water diffusion measurements of I-A+ show that proton conductivities are low (10−7–10−6 S cm−1) under low relative humidity (RH), and protons mostly migrate as H3O+ with H2O as vehicles (vehicle mechanism). The proton conductivity of I-A+ increases with the increase in RH and is largely dependent on the types of alkali metal ions. I-Li+ shows a high proton conductivity of 1.9 × 10−3 S cm−1 (323 K) and a low activation energy of 0.23 eV under RH 95%. Under high RH, alkali metal ions with high ionic potentials (e.g., Li+) form a dense and extensive hydrogen-bonding network of water molecules with mobile protons at the periphery, which leads to high proton conductivities and low activation energies via rearrangement of the hydrogen-bonding network (Grotthuss mechanism).

Graphical abstract: Proton conduction in alkali metal ion-exchanged porous ionic crystals

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Publication details

The article was received on 10 Jul 2017, accepted on 05 Sep 2017 and first published on 06 Sep 2017


Article type: Paper
DOI: 10.1039/C7CP04619G
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    Proton conduction in alkali metal ion-exchanged porous ionic crystals

    S. Uchida, R. Hosono, R. Eguchi, R. Kawahara, R. Osuga, J. N. Kondo, M. Hibino and N. Mizuno, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP04619G

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