Structures of water at electrified interfaces: Microscopic understanding of electrode potential in electric double layers on electrode surfaces

The origin of an “immersed gap” (the difference between the UHV and electrochemical situation) is attributed to charge transfer from water molecules to metal electrodes, and the potential drop near the electrified interface depends on the orientation of water dipoles of cationic or anionic water at inner and outer Helmholtz layer. Water molecules in an electric double layer exhibit an ordered and a disordered structure at negative and positive electrode potentials, respectively. Therefore, potential polarization (negative or positive electrode potential application) from an equilibrium potential operates the electrified interface to cause increased or decreased ordering, orientation and charge transfer of water molecules as well as water dissociation on the electrode surfaces.