## Results and Discussion
### Electrochemical Characterization

Table 1: Electrochemical corrosion study of WEP coatings with nano-PDA@GO-TiO\({}_{2}\) composites in 3.5% NaCl corrosive conditions. Figure 10: Polarization curves of PGT/WEP coatings immersed in 3.5 wt.% NaCl aqueous solution for 7 days. to \(6.37\times 10^{2}\Omega\)-cm\({}^{2}\) after 30 days of continuous immersion, indicating the diffusion of Corrosive ion into the WEP coatings and resulting in loss of protective ability of the coating. In comparison, PGT-0.5%/WEP, PGT-1%/WEP, GPT-2%/WEP, GPT-3%/WEP coatings, the initial impedance modulus at \(|Z|_{0.01}\) were 5.31 \(\times\) 10\({}^{4}\)\(\Omega\)-cm\({}^{2}\), 6.91 \(\times\) 10\({}^{4}\)\(\Omega\)-cm\({}^{2}\), 8.62 \(\times\) 10\({}^{4}\)\(\Omega\)-cm\({}^{2}\), and 6.67 \(\times\) 10\({}^{4}\)\(\Omega\)-cm\({}^{2}\), and these values decreased to 5.23 \(\times\) 10\({}^{3}\)\(\Omega\)-cm\({}^{2}\), 7.34 \(\times\) 10\({}^{3}\)\(\Omega\)-cm\({}^{2}\), 1.02 \(\times\) 10\({}^{4}\)\(\Omega\)-cm\({}^{2}\), 6.53 \(\times\) 10\({}^{3}\)\(\Omega\)-cm\({}^{2}\) after immersion of 30 days, which is one to two orders of magnitude higher than the pure WEP coating during the whole immersion process. This is mainly due to the good dispersibility of the nano-PDA@GO-TiO\({}_{2}\) composites in the aqueous epoxy matrix. Obviously, the GPT-2%/WEP coating exhibited the highest impedance modulus than those of other coatings during the whole immersion process, which suggesting that the coating possessed the best anticorrosion performance. In order to further analyze the protective properties of the PGT/WEP coatings for the substrate the equivalent circuit was used to fit the EIS curve, as shown in Figure 11d-f. In the circuit, Rs, Rc, and Rc  
Figure 11: Bode impedance diagram, Bode phase diagram and Nyquist diagram of PGT/WEP coating soaked for 1 day, 15 days, and 30 days, respectively. (A), (B) The equivalent circuits. represented the electrolyte resistance, coating resistance and charge transfer resistance, respectively. Qc and Qdl represented the coating capacitance and the electric double layer (steel/colution) capacitance. The corrosion process of the coating is mainly divided into two stages: the period in which the corrosive medium has not penetrated to reach the coating/base metal interface is called the first stage, and the A model is used in this stage. As the corrosive medium penetrates the interface of the coating/substrate metal and forms a corroded microbattery, the impedance spectrum that was measured at this time has two times constants, which is called the second stage, and the B model is used in this stage [52]. From Figure 11c, it is clear that the pure WEP coating begins to appear the second time constants during immersion for 15 days. At the same time, the GPT-3%/WEP coating shows a similar situation. It is worth nothing that the GPT-2%/WEP coatings always maintained the highest Rc and phase angle values, indicating that the GPT-2%/WEP coating has a strong barrier effect. As shown in from the Nyquist diagram of Figure 11a-f, that the capacitance arc of the pure WEP coating is much smaller than the capacitance arc of the GPT/WEP coating, and the GPT-2%/WEP coating has a higher capacitance arc. After 15 days of immersion for 30 days, as in Figure 10f, the GPT-2%/WEP coating still exhibited a larger capacitance arc than the other coatings. Because of the nano PDA@GO-TiO\({}_{2}\) composites can block the micropores in the coating to form a shielding layer. Effectively blocking the infiltration of corrosive media such as O\({}_{2}\), Cl\({}^{-}\), and H\({}_{2}\)O, thus greatly reducing the corrosion rate and significantly improving the long-term anticorrosive properties of water borne epoxy coatings.