Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.