Ordering of a Nanoconfined Water Network around Zinc Ions Induces High Proton Conductivity in Layered Titanate

• Published in: Chemistry of materials Vol. 34; no. 9; pp. 3967 - 3975
• Main Authors: Kang, Seongkoo, Reeves, Kyle G., Aguilar, Ivette, Porras Gutierrez, Ana Gabriela, Badot, Jean-Claude, Durand-Vidal, Serge, Legein, Christophe, Body, Monique, Iadecola, Antonella, Borkiewicz, Olaf J., Dubrunfaut, Olivier, Fayon, Franck, Florian, Pierre, Dambournet, Damien
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.05.2022
• Subjects: Chemical Sciences
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.1c04421

We demonstrated that the chemical intercalation of Zn2+ ions within the interlayer space of the structure of a disordered layered titanate results in a drastic increase of the room-temperature bulk proton conductivity from 8.11 × 10–5 S m–1 for the pristine to 3.7 × 10–2 S m–1 for Zn-titanate. Because of the crystallographic disordered nature of these compounds, we combined different techniques to establish the structural-transport relationships. The pair distribution function revealed that upon chemical insertion of Zn2+, the local lepidocrocite arrangement is maintained, providing a suitable model to investigate the effect of chemically intercalated ions on the transport properties and dynamics within the interlayer space. Broadband dielectric spectroscopy (50 to 1010 Hz) enabled establishing that Zn2+ inclusion promotes proton-hopping by self-dissociation of H2O molecules yielding high proton mobility. Using Zn–K edge extended X-ray absorption fine structure and chemical analyses (EDX, TGA, 1H NMR), Zn2+ ions were shown to be stabilized by ZnCl2(H2O) complexes within the interlayer space. Such complexes induce an increase of the H-bonding strength as evidenced by 1H NMR, yielding a fast proton motion. Molecular dynamics simulations highlighted proton transfer between water molecules from the structural interlayer and bonded to Zn2+ ions. The increasing interactions between these water molecules favor proton transfer at the origin of the fast bulk proton conductivity, which was assigned to a Grotthuss-type mechanism taking place at a long-range order. This work provides a better understanding of how ion–water interactions mediated ionic transport and opens perspectives into the design of ionic conductors that can be used in energy-storage applications.