Corrosion Study of Zinc, Nickel, and Zinc-Nickel Alloys in Alkaline Solutions by Tafel Plot and Impedance Techniques

The article describes the use of Tafel plot and electrochemical impedance spectroscopy (EIS) techniques, in order to study the corrosion process of pure zinc, nickel, and synthetic Zn-Ni alloys in various concentrations (0.25 to 1 M) of KOH solution in a temperature range 298 K to 328 K (25 °C to 55 °C). The corrosion rate increases with increasing both concentration of KOH and temperature for all investigated electrodes. The results showed that the increase in Ni content improves the corrosion resistance and increases the barrier of activation energy, and the higher value of corrosion resistance is obtained at 10 pct Ni. The electrochemical measurements using two mentioned techniques are in good agreement with the results of microhardness in that the microhardness gradually increases with increasing Ni content in the alloy. Thus, the corrosion rate of these alloys is significantly reduced compared with that of pure zinc. It is observed that the Warburg tail at low frequency completely disappears at the applied potentials in the case of alloy IV (10 pct Ni) only. This indicates that the diffusion of Zn ion species is strongly reduced. Therefore, addition of Ni to Zn has a beneficial effect, because it leads to lower loss of anode material. The results obtained at certain positive potential (+420 mV vs SCE) exhibited that the semicircle diameter in the case of alloys is lower compared with that of pure zinc. This result means that the values of the charge transfer resistance (Rct) in the case of alloys are decreased, due to the breakdown of the oxide layer at this potential. This behavior can be considered as an important criterion for a good battery anode, due to reactivation of the alloy surface at certain positive potential (+0.420 V vs SCE) and suppression of hydrogen gas compared with those of pure zinc.