Electrochemical impedance studies of modified Ni-P and Ni-Cu-P deposits in alkaline medium

Ni-P and Ni-Cu-P deposits were supported over the commercial carbon using the electroless plating technique. The formed samples were characterized by applying SEM, XRD and EDX analyses. An amorphous Ni-P surface was obtained with 73.70 wt% Ni and 11.45 wt% P. The addition of copper to the plating bath reduces the deposited amount of nickel and phosphorus. The electrochemical performance of these deposits has been investigated in 0.1 M KOH solution using electrochemical impedance spectroscopy (EIS) measurements. The effect of pH, deposition time and temperature of the plating bath on the impedance characteristics of the two deposits was studied. It was found that the resistance (R_T) and relative thickness (1/C_T) of the two coatings in 0.1 M KOH solution increase with increasing either pH or deposition time or temperature of the plating bath. Our results indicate that Ni-Cu-P deposit has more corrosion resistance and lower corrosion current density (i_corr) value than Ni-P deposit under different conditions. EIS results were well confirmed by potentiodynamic polarization and cyclic voltammetry techniques.