Orientation control and characterization strategies towards developing 2D materials-based composite coatings for corrosion protection on metals: Progresses and challenges

Recently, two-dimensional (2D) materials have been widely investigated for corrosion protection on metals owing to high specific surface area, high aspect ratio, physical barrier, and chemical stability. The 2D films and 2D nanosheets-based composite coatings have drawn much attention for the application in anti-corrosion, mainly including graphene (Gr), boron nitride (BN), and MXene. However, the anti-corrosive composite coatings still face challenges in structural design, orientation control, quantitative characterization, and anti-corrosion mechanism. In this review, the orientation control and characterization strategies of these 2D nanosheets (Gr, BN, MXene) -based composite coatings for corrosion protection on metals are comprehensively reviewed. First, the corrosion resistance of the 2D films and the importance of the orientation control of 2D nanosheets in composite coatings for the anticorrosive properties are briefly introduced. Second, the regulation methods and characterization strategies of the orientation of 2D nanosheets in the coatings are discussed in detail. Third, the progresses of the effect of orientation on the anti-corrosive properties and mechanisms of the composite coatings are presented. Finally, the challenges in the structural design and characterization of the 2D nanosheets-based anti-corrosion coatings are prospected, and the future developments are discussed.