The charged interface between Pt and water: First principles molecular dynamics simulations

The charged interface between a platinum electrode and an aqueous solution is investigated by first-principles molecular dynamics simulations in which charges in the system are controlled by the effective screening medium method under periodic boundary conditions. H₃O⁺ and OH are located above or on the Pt surface. Water molecules rotate to screen the electric field induced by the charge accumulated on the Pt surface. The time-averaged electrostatic potential near the Pt surface is structured with a flattened "bulk" region. The potential difference between the Pt Fermi level and the bulk potential is proportional to the charge and is used to estimate the Pt electrode potential via the PZC (potential of the zero charge). The surface charge significantly polarizes the water molecules near the Pt surface. The OH stretching frequency of molecules on the negatively charged (7 ∼ 14 μC/cm²) Pt electrode shift to lower values (red shift) by 100 ∼ 200 cm^-1. For the positively charged Pt lattice, a complex feature results from a charge transfer reaction that takes place there. The electrode structure is also influenced by accumulated charge as the distance between the top surface Pt layer and the next layer underneath increases for both the negatively and positively charged surfaces.