Microscopic EDL structures and charge-potential relation on stepped platinum surface: Insights from the ab initio molecular dynamics simulations.

The microstructural features and charge-potential relation of an electric double layer (EDL) at a stepped Pt(553)/water interface are investigated using ab initio molecular dynamics simulation. The results indicate that the chemisorbed O-down water molecules gather at the (110) step sites, while the (111) terrace sites are covered by the H-down water molecules, which greatly weakens the push-back effect of interface water on the spillover electrons of the stepped surface and, therefore, results in a much more positive potential of zero charge (PZC) than the extended low-index Pt surfaces. It is further revealed that around the PZC, the change in the surface charge density is dominated by the change in the coverage of chemisorbed water molecules, while EDL charging is the main cause of the change in the surface charge density at potential away from the PZC, thus leading to an S-shaped charge-potential relation and a maximum interface capacitance around PZC. Our results make up for the current lack of the atomic-scale understanding of the EDL microstructures and charge-potential relation on the real electrode surfaces with plentiful step and defect sites.