Abstract
We demonstrated that the chemical intercalation of Zn$^{2+}$ 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 x 10$^{-5}$ S.m$^{-1}$ for the pristine to 3.7 x10$^{-2}$ 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. Pair distribution function revealed that upon chemical insertion of Zn$^{2+}$ , the local lepidocrocite arrangement is maintained, providing a suited model to investigate the effect of chemically intercalated ions on the transport properties and dynamics within the interlayer space. Broadband dielectric spectroscopy (50 to 10$^{10}$ Hz) enabled to establish that Zn$^{2+}$ inclusion promotes proton-hopping by self-dissociation of H$_2$O molecules yielding high proton mobility. Using Zn-K edge EXAFS and chemical analyses (EDX, TGA, $^1$H NMR), Zn$^{2+}$ ions were shown to be stabilized by ZnCl$_2$ (H$_2$O) complex within the interlayer space. Such complexes induce an increase of the H-bonding strength as evidenced by $^1$H NMR, yielding a fast proton motion. Molecular dynamic simulations highlighted proton transfer between water molecules from structural interlayer and bonded to Zn 2+ ions. The increasing interactions between these water molecules favors proton transfer at the origin of the fast bulk proton conductivity, which was assigned to a Grotthuss-type mechanism taking place at 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.