Understanding the role of oxygen vacancy on corrosion resistance of coating containing cerium oxide nanoparticles doped with cobalt as highly effective corrosion inhibitors

Cerium salts have received significant attention for their potential in constructing protective materials on metallic substrates. However, there are few studies on the use of cerium oxide nanoparticles (CeO2 NPs) as corrosion inhibitors, and even fewer on the mechanisms by which they protect steel. In this work, we discuss the effect of oxygen vacancy on the corrosion resistance of an epoxy coating containing cobalt-doped CeO2 NPs in detail. To evaluate the effect of oxygen vacancy on corrosion resistance, we obtained CeO2 and Ce7CoO16 NPs, as well as KH560-Ce7CoO16 NPs, through a controlled facile sol-gel method. The results indicated that KH560-Ce7CoO16 NPs had a higher percentage of Ce3+ and oxygen vacancy (Ov) compared to CeO2 and Ce7CoO16 NPs. Specifically, KH560-Ce7CoO16 NPs were found to have 32.12% Ce3+ and 46.65% Ov, whereas CeO2 and Ce7CoO16 nanoparticles had lower Ce3+ and Ov ratios, with values of 23.46% and 27.30%, and 29.79% and 45.60%, respectively. The micromorphology of CeO2, Ce7CoO16, and KH560-Ce7CoO16 in the epoxy matrix indicated that the addition of 2% KH560-Ce7CoO16 NPs achieved a homogeneous dispersion. Compared to the CeO2 and Ce7CoO16 NPs, KH560-Ce7CoO16 NPs at an appropriate concentration exhibited excellent corrosion resistance performance for the substrate, as evaluated by electrochemical and salt spray tests. We propose that two mechanisms synergistically contribute to the corrosion protection. Firstly, due to oxygen reduction, insoluble cerium hydroxide is formed at the cathodic sites. Secondly, Ov acts as a charge capture center, facilitating the transfer of electrons lost by the anode to the oxygen vacancies and blocking the OH– generated by the cathodic reaction, as well as the new substances generated by the Fe2+ produced by the anodic reaction, which ultimately slows down the corrosion chemical reaction process. This work provides a novel understanding of cerium oxide nanoparticles as corrosion inhibitors, and presents an effective strategy for achieving excellent corrosion resistance performance in a corrosive environment.