Electric potential near a charged metal surface in contact with aqueous electrolyte

Abstract

The time independent electric potential due to water and a lithium ion near a charged metal surface is calculated by space and ensemble averaging of trajectories generated by a molecular dynamics simulation. Since the cation does not contact adsorb, variations in the electric potential near the metal surface are due to water oriented in the electric field of the charged surface. The potential is decomposed into separate contributions from monopoles (from the ions), and dipoles, quadrupoles and octopoles (from the water molecules). At distances greater than about 0.5 nm from the electrode (two to three water molecules) the potential is 'flat' with the quadrupole contributing most due to a near cancellation of the ion and water dipole components. Approaching the surface, weak features are encountered due to water packing and then a big oscillation due to water oriented in a layer next to the electrode. None of these effects are described in theories that approximate water as a continuum fluid.