Electrochemical Evaluation of Coordination Polymers as Efficient Corrosion Inhibitors for Iron in Aggressive Media

Corrosion creates major economic and environmental problems across industries. Corrosion prevention needs to be ensured and coordinated throughout all branches of the national economy [1].

The corrosion inhibitory performance of two coordination polymers (CPs) toward iron corrosion in a saline medium at pH 2.5 was investigated, motivated by the recognized potential of organic compounds incorporating N, S, and O heteroatoms and π-conjugated electronic systems as effective corrosion inhibitors[2-4]. 

Due to its extended aromatic structure, conjugated double bonds, and heteroatoms, the CP molecule fulfills the theoretical criteria needed to form a protective layer that effectively covers active sites on the metal, thereby preventing aggressive species from reaching the surface.

Our objective is determining the anticorrosion protection of: [Cu₃L₂(NO₃)]NO₃・2H₂O and [Zn₂L(CH₃COO)₂]·2H₂O. Different concentrations of inhibitors were used: 50 ppm, 100 ppm and 150 ppm. The evaluation of the performance is determined using electrochemical impedance spectroscopy (EIS) and potentiometric methods (CP). EIS and CP measurements provide accurate data within a short testing time, allowing for the prediction of the long-term performance of the coatings. The results obtained from the polarization curves are in agreement with those obtained from EIS measurements.

The experimental findings reveal that a concentration of 50 ppm is sufficient to achieve low corrosion current densities during short-term exposure to the saline medium, while extended immersion requires an optimal inhibitor concentration of 100 ppm to ensure enhanced corrosion protection. For both inhibitors the corrosion rate decreased by two orders of magnitude compared with the untreated iron sample.