(Invited) Assembly of Electrochemically Reduced Graphene Oxide, at the Nano and Microscales, for the Preparation of Functional Coatings.

Abstract

Graphene oxide (GO) presents the advantage of being easily dispersed in water, which facilitates the assembly of nano and microstructures by numerous methods, in order to form uniform and thickness-controlled functional coatings. For example, the electrophoretic deposition (EPD) is one of the most used techniques to produce anticorrosive coatings onto metals, including GO and reduced graphene oxide (rGO) coatings. We have used a variation of the EPD process of GO, which consisted in changing the GO’s charge to positive values allowing the electrophoretic deposition of GO onto the cathode (cEPD). The coating diminished by three times the corrosion rate of carbon steel. The preparation of these coatings also implies the understanding of the mechanism through which the electrochemical reduction of the GO is carried out.1 An electrochemical reduction mechanism of GO involving hydrogenation/hydrogenolysis reactions is suggested as the main reason to achieve an effective anticorrosive-coating by cEPD in comparison to the films produced by an anodic EPD. For this reason, we studied the electrochemical reduction of GO in aqueous and organic media containing H+ donor, to investigate the role of H+ in the reduction mechanism. In aqueous electrolyte, in both acid and basic pH, the H+ enhanced the removal of oxygenated groups by electrochemical reduction and promoted the loss of some sp2 domains due to hydrogenation reactions of the graphitic domains. The electrochemical reduction of GO in organic media, free of H+, resulted in the restoration, to some degree, of the sp2 domains. However, the removal of the oxygenated groups seemed hindered when compared to the same process in presence of H+ donor, in the organic solvent, at the same potential intervals. Considering that through these studies it is possible to choose a route for the preparation of functional films, recently we proceeded to modify electrochemically the rGO through with 5-membered alkyne chains. The resulting rGO film presented lower conductivity, due to the loss of graphitic domains, and an increased hydrophobicity. The modified rGO film was evaluated as an anticorrosive coating for carbon steel, showing a better protection from corrosion in comparison to the protection granted by the regular rGO film. [1] J.A. Quezada-Rentería, L.F. Chazaro-Ruiz, J.R. Rangel-Mendez, Synthesis of reduced graphene oxide (rGO) films onto carbon steel by cathodic electrophoretic deposition: Anticorrosive coating, Carbon 122 (2017) 266-275.