Electrical double layer at the mineral-aqueous solution interface as probed by XPS with fast-frozen samples

The electrical double layer (EDL) at the mineral-aqueous solution interface is a typical example of intrinsic charging effects. As a key feature of the interface, the EDL determines its chemical composition and electrical field. The ability of the XPS technique to probe this phenomenon on fast-frozen samples is presented. It allows the quantification of counter-ions and the direct observation of interface chemical processes, such as ion pairing, specific adsorption and ligand exchange reactions. It is also shown that binding energy shifts arising due to water removal provide an experimental possibility to estimate surface potentials and their distribution within the EDL. Future directions and perspectives of the technique are shortly discussed.