Study of environmental barriers based on engineered electrochemically reduced graphene oxide for the protection of carbon steel against corrosion

Abstract

"Owed to the modern way of living of the human race, the corrosion of metals is a problem with dramatic economic, social and environmental consequences. Specifically, steel is one of the most important metals used nowadays, since it is employed in almost every activity of the modern age, thus, the research and development of new technologies for retarding its corrosion is of paramount importance. Recently, the use of graphene-based materials as coatings for the protection of metals has received considerable attention. This work reports, for the first time, the successful use of electrochemically reduced graphene oxide (ErGO) films as anticorrosive coatings for the protection of carbon steel against corrosion. ErGO films were assembled onto carbon steel substrates by different assembly methods, such as cathodic electrophoretic deposition (cEPD) and drop coating, and with their physicochemical properties were engineered by the conditions used during the electrochemical reduction of the films. The results showed that the cEPD of graphene oxide (GO) to produce pure ErGO films can be achieved by adding Ca2+ and fixing the pH of the GO suspension to 6, allowing the simultaneous deposition and electrochemical reduction of GO. These films achieved a 3-times decrease in the corrosion rate of carbon steel. This result contrasted with published studies that concluded that the protection of carbon steel with reduced graphene oxide (rGO) films was not possible. A deep investigation on the electrochemical reduction mechanism of GO was performed to explain the success achieved by our ErGO film, which focused on unraveling the role of H+ in the removal of oxygenated groups (O-groups) and the formation of defects in the graphene sheets. The results showed that the presence of H+ improves the efficiency of removal of O-groups, due to a hydrogenation/hydrogenolysis mechanism, obtaining ErGO films with higher C/O ratios. However, the presence of H+ also caused the xiv hydrogenation of graphitic domains, rendering a more defective material. Nevertheless, these defects were proved to be the key of the success of the ErGO film as an anticorrosive coating, since they do not compromise the barrier property of graphene sheets. Additionally, the ErGO films presented one of the lowest conductivities ever reported, with only 13.3 S cm-1. The latter was further decreased by the electrochemical modification of the ErGO film with alkyne chains. The low conductivity of both films allowed them to avoid the occurrence of galvanic corrosion when coated on a carbon steel substrate. Additionally, the alkyne chains increased the hydrophobicity of the coating, allowing it to achieve a 96-times decrease of the corrosion rate of carbon steel."