## 3 Results and Discussions  
### Electrochemical Analysis  
Electrochemical changes occurring during the immersion of carbon steel in a 3% NaCl solution, with and without EEA4 NB, were explored by interpreting an electrical signal arising from the metal interface. This signal provides essential information regarding metal corrosion. The evaluation of metal corrosion in saline solution can be performed through OCP, EIS, and PDP measurements. From the OCP curves, it was observed that for carbon steel immersed in the blank solution, there was a decrease in potential. The potential decreased from approximately \(-0.55\) V at the beginning of immersion to approximately \(-0.68\) V after 1 h of immersion. This potential decrease is attributed to the penetration of Cl\({}^{-}\) ions through the protective oxide layer present on the metal surface. The oxide layer offers only partial protection, and its dissolution is not entirely prevented. It is reported that iron oxides dissolve under the attack of chloride ions, with an increased applied potential in the positive direction [34]. In the case of carbon steel immersed in the testing solutions, the initial potential of carbon steel shifted to a higher potential due to the formation of a protective film on the carbon steel (electrode) surface. After 505 s, the OCP value tended to stabilize, indicating a stable layer deposited on the metal surface. As the concentration of EEA4 NB increased, the potential value after 1 h of immersion shifted to more positive values, suggesting the formation of a protective layer on the metal surface. The EIS technique was employed to study the nature of the electrochemical processes occurring at the carbon steel (electrode)/3% NaCl interface and to understand the influence of EEA4 NB on the iron dissolution process. The impedance curves for the Fe electrode recorded in the 3% NaCl solution with different concentrations of EEA4 NB are presented as Nyquist plots in Figure 1a and as Bode plots in Figure 1b. The electrochemical equivalent circuit (EEC) considered for modeling the EIS data is shown in Figure 1c. Figure 1: Impedance curves: (**a**) Nyquist plots, (**b**) Bode plots, and (**c**) the electrochemical equivalent circuit (EEC) used for fitting experimental data for carbon steel electrodes immersed in a saline solution with varying EEA4 NB concentrations. The Nyquist plots display a single depressed semicircle that changes with the addition of inhibitor molecules, with the diameter of the semicircle increasing alongside the EEA4 NB concentration. These results suggest surface roughness and heterogeneity. Similar conclusions are drawn from the Bode plots in Figure 1b, where only one peak is observed at the middle frequency range both in the absence and presence of EEA4 NB. The magnitude of the capacitive loop in Figure 1a, as well as the impedance modulus in the low-frequency domain (Figure 1b), increases with the inhibitor concentration. The impedance data are fitted using the circuit in Figure 1c. The EEC used for the interpretation of EIS data includes a resistance (\(R_{\text{s}}\)) representing the solution resistance between the reference electrode and working electrode. This is placed in series with a parallel connection between a capacitor (\(C_{\text{eff}}\)), signifying double-layer capacitance, and a resistance (\(R_{\text{ct}}\)), representing charge transfer resistance. The electrochemical parameters determined with EEC are listed in Table 1.  
In the saline solution, the increase in EEA4 NB concentration points to a significant improvement in the charge-transfer resistance (\(R_{\text{ct}}\)) and a decrease in \(C_{\text{eff}}\) values. A high \(R_{\text{ct}}\) value usually indicates a slower corrosion process due to the adsorption of inhibitor molecules on the electrode surface. The decreasing trend observed for \(C_{\text{eff}}\) values could be associated with the decrease in the local dielectric constant or the reduction in the electrode exposure area as a result of the protective layer developed on the electrode surface.