Morphology modification of electrodeposited superhydrophobic nickel coating for enhanced corrosion performance studied by AFM, SEM-EDS and electrochemical measurements

In this work, an electrodeposited superhydrophobic nickel film with apparent contact angle of 156 degrees was fabricated using different contents of H3BO3 as a morphological modifier to effectively improve the corrosion resistance of the underlying copper substrate. Atomic force microscopy and scanning electron microscopy analysis allowed visualization of growth mechanism and morphology of the electrodeposited coating in the presence and absence of H3BO3. The results showed that H3BO3 considerably effects on morphology of coating by its hindering property that leads to form micro and micro-nanocones hierarchical structures with the mechanism of screw dislocation-driven growth. The spontaneous adsorption of airborne hydrocarbon contaminants on the nickel micro-nanostructures enhances the hydrophobicity of the surface. Cyclic voltammetry and X-ray diffraction provide other evidences of the boric acid hindering effect. The quantitative analysis of atomic force microscopy results showed that after about 5 months exposure to air, the roughness value has been decreased and apparent contact angle has been decreased to 127 degrees. Finally, corrosion behavior of the superhydrophobic nickel film was investigated in 3.5 wt.% NaCl by means of AC/DC electrochemical methods. Regarding potentiodynamic polarization and electrochemical impedance spectroscopy, the superhydrophobic nickel film (Cassie-Baxter state) exhibited five times greater corrosion resistance in comparison with fresh nickel film (Wenzel state).