The effects of an inorganic corrosion inhibitor on the electrochemical behavior of superhydrophobic micro-nano structured Ni films in 3.5% NaCl solution

The application of hierarchically micro-nano structured superhydrophobic Ni films with increased surface roughness is known as an attractive corrosion protection strategy because the chemically modified film with a low surficial free energy is capable of keeping water molecules and aggressive species away from the coating/electrolyte interface by trapping air pockets within the micro-nano structured layer. Furthermore, corrosion inhibitors are widely used for corrosion mitigation in a broad range of industrial applications. This study tends to investigate the corrosion resistance of electrodeposited superhydrophobic Ni films in the presence of sodium molybdate (0 M, 0.03 M, 0.06 M, 0.1 M) as an inorganic corrosion inhibitor in a 3.5 wt% NaCl solution at 25 °C, up to 120 h. The micro-nano structured superhydrophobic Ni film with a mean thickness of 4 μm was electrodeposited on a Cu substrate via a two-step electrodeposition process at 60 °C including 8 min of electrodeposition at a constant current density of 20 mA/cm2, followed by 1 min of electrodeposition at a constant current density of 50 mA/cm2 and a subsequent chemical modification step in stearic acid solution. Investigation of surface topography of the film by atomic force microscopy technique (AFM) revealed that the root-mean-square of height and the skewness of the film were equal to 14.4 nm and 0.21, respectively. The morphology of the film consisted of micro-nano cones in the size range of 50 to 1000 nm. The superhydrophobic film demonstrated a passivation behavior and a pitting potential. The EIS study identified the Ni film as a non-ideal capacitor and an equivalent circuit model with two parallel time-constants fitted to the EIS data. Upon 120 h of immersion of the superhydrophobic film in the electrolyte in the presence of 0.1 M of sodium molybdate, the corrosion inhibitor efficiency of about 80% was achieved and the Ni film demonstrated the best passivation behavior and the lowest corrosion current density.