Effect of electropolishing conditions on nanostructured anodized surfaces for enhanced superhydrophilicity and corrosion resistance of 304 and 316 L Stainless Steels

• Electropolishing conditions (None, EP1, and EP2) created distinct dimple patterns that shaped anodic oxide growth. • Viscous-layer stability during EP influenced dissolution and dimple evolution. • EP1 generated a hierarchical porous oxide layer with larger pores, while EP2 produced a denser layer with smaller pores. • EP1 exhibited superhydrophilic/oleophilic behavior, while EP2 showed moderate wettability and improved durability. • EP2 showed the best corrosion resistance with highest R film and R ct values. This study shows that variations in electropolishing (EP) conditions influence the stability and uniformity of the interfacial viscous layer on SUS 304 and SUS 316 L, resulting in distinct dissolution behavior and nanoscale morphology in the anodic oxide films. Under the EP1 condition, the thicker and less uniform viscous layer promoted localized dissolution, which formed a dual-layered oxide with wide and shallow polygonal pores, and with pronounced superhydrophilic and oleophilic wetting. In EP2, a thinner viscous layer was established, resulting in a denser nanoporous oxide with smaller and more uniform pores and moderate wettability. Importantly, these electropolishing-induced dimple structures acted as morphological templates, causing the anodic oxide films to develop markedly different pore sizes and thicknesses even under identical anodization conditions. XPS confirmed EP-induced redistribution of alloying elements (Cr, Ni, Mo) and the growth of multicomponent oxides after anodization. Electrochemical measurements demonstrated that EP2 significantly enhanced passivation performance, producing lower corrosion current density and higher Rfilm and Rct compared with untreated samples. Overall, this work clarifies how electropolishing conditions, in combination with alloy-dependent dissolution behavior, determine dimple formation, nanopore evolution, and corrosion performance. These insights identify EP2 as an effective pretreatment route for producing dense, stable oxide films with enhanced long-term durability on stainless steels. Importantly, this study demonstrates that variations in electropolishing conditions generate distinct micro-dimple morphologies, which in turn dictate the pore structure and thickness of the anodic oxide layer even under identical anodization parameters.