Outer Helmholtz Plane of the Electrical Double Layer Formed at the Solid Electrode–Liquid Interface

Electrical double layer: The detailed outer Helmholtz plane (HP) structure composed of Cs+ above c(2×2)-Br on Ag(100) electrode using in situ surface X-ray diffraction in electrochemical environments is described. Hydrated Cs+ cations are accommodated in the hollow sites of the c(2×2)-Br layer. The coverage of Cs+ and the distance of the Cs+ layer from the surface depend on the electrode potential. A single layer of water is intercalated between the inner and outer HP ions (see picture).