Characterization of the Outer Layer Nanostructure in the Electrochemical Response of Stainless Steel in Aqueous Sodium Hydroxide

The outer layer nanostructure of stainless steel’s passive film in 0.1 M NaOH has been studied by electrochemical atomic force microscopy and the role of the outer layer in the electrochemical response of stainless steel has been characterized. The outer layer is mainly composed of nanoscale particles whose average diameter is up to 13.14 ± 3.52 nm at the end of the formation period. The formation process is characterized by the nucleation, growth, and contact of oxide particles. Based on the study on the outer layer nanostructure, the gaps/boundaries between particles in the outer layer should be diffusion paths for ions across the layer. The electrochemical impedance spectroscopy analysis revealed that the ion diffusion resistance first increased and then remained stable due to the three-dimensional growth of nanoscale particles.