Ni-graphene oxide composite coatings: Optimum graphene oxide for enhanced corrosion resistance

Ni-Graphene oxide (GO) composite coatings were electrodeposited over mild steel substrate. The coatings exhibited compact and crack free morphology. Incorporation of GO facilitated grain growth along low energy (111) and (200) atomic planes without any significant alteration in the crystallite size. Compositional analysis suggested uniform distribution of GO within the coating for lower GO concentration. Whereas for higher GO concentrations, agglomeration and non-uniform distribution of GO within the coating microstructure was noticed. Corrosion behaviour of coatings was studied by electrochemical impedance spectroscopy and potentiodynamic polarisation techniques. It was observed that the corrosion rate of the coating initially decreased with the addition of GO. After an optimum GO concentration which produced the lowest corrosion rate, further addition of GO resulted in increase in the corrosion rate. The initial decrease in the corrosion rate was attributed to the coating growth along the low energy low index planes and the impermeability of the GO to the electroactive media. The increase in the corrosion rate beyond the optimum was attributed to the GO agglomeration which caused inhomogeneous distribution of GO in the coating and relatively non-uniform coating morphology.