To further understand the role of O2 in a ZAB setup, electrochemical impedance spectroscopy (EIS) measurements are conducted at the open circuit potential (OCP) using a sine wave signal of 10 mV amplitude and within a frequency range of 100 kHz to 1 Hz in N2 as well as in O2 environments in alkaline medium. The Nyquist plots given in Fig. B show semicircular loops, indicating a charge transfer process or the corrosion process, as mentioned in literature. The best fitted Randles' circuit is shown in the inset corresponding to specific adsorption of ionic species at the surface, where their presence is proven in the later part. Here, the Rs represents the ohmic resistance, related to uncompensated contact and electrolyte resistance, Rct denotes the anodic charge-transfer resistance, while Qd represents the double-layer capacitance. Rf and Qf correspond to the resistance and capacitance of the ZnO film on the metal surface. The charge transfer resistance value is seen to be 513 Ω in O2 whereas it is found to be 3428 Ω in N2 environment, indicating a charge transfer process on Zn surface in presence of O2.