Ionic Properties of Oxide Gels

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Abstract
Oxide gels are actually hydrous oxides. Water adsorption and dissociation occur at the surface of the oxide network leading to charged particles surrounded by an acid or basic aqueous medium. They can be considered as particle hydrates. Fast proton conduction is observed arising from proton diffusion through the adsorbed water layers. Proton conductivity is actually strongly related to the water adsorption isotherm.Ion exchange readily occurs at the oxide-solution interface when the gel is dipped inside an aqueous solution. Some inorganic gels exhibit a layered structure similar to that of sheet silicates. Ion exchange can then be described as an intercalation process. It can be used as a synthetic route toward new compounds.Electrochemical insertion within the oxide network is highly reversible. This is due to the open structure of the gel and the mixed valence behavior of the transition metal oxide. Reversible cathodes or electrochromic layers have been made from V2 O5, W03or TiO2gels. Thin films or pressed pellets can be easily made from oxide gels. They are therefore good candidates for making "all gel" micro-ionic devices.

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