Abstract
In recent years, ultrathin two-dimensional (2D) coatings, e.g., graphene (Gr) and hexagonal boron nitride (h-BN), are intriguing research foci in the field of anticorrosion because their high air stability, excellent impermeability, high optical transparency, and atomistic thickness have endowed them with attractive anticorrosion applications. The microstructure of 2D coatings, coating–substrate interactions, and properties of 2D coatings on substrates in a variety of environmental conditions (e.g., at different temperatures, stresses, and pH values) are the key factors governing the anticorrosion performance of 2D coatings and are among the central topics for all 2D-coating studies. For many conventional experimental measurements (e.g., microscopy and electrochemical methods), there exist challenges to acquire detailed information on the atomistic mechanisms for the involved subnanometer scale corrosion problems. Alternatively, as a precise and efficient quantum-mechanical simulation approach, the first-principles calculation based on density-functional theory (DFT) has become a powerful way to study the thermodynamic and kinetic properties of materials on the atomic scale, as well as to clearly reveal the underlying microscopic mechanisms. In this review, we introduce the anticorrosion performance, existing problems, and optimization ways of Gr and h-BN coatings and summarize important recent DFT results on the critical and complex roles of coating defects and coating–substrate interfaces in governing their corrosion resistance. These DFT progresses have shed much light on the optimization ways towards better anticorrosion 2D coatings and also guided us to make a prospect on the further development directions and promising design schemes for superior anticorrosion ultrathin 2D coatings in the future.
Highlights
Introduction iationsCorrosion usually is an undesirable phenomenon since it negatively affects the performance of refined metal products related to infrastructures, water conservancy projects, transportation, energy, manufacturing, and public services and leads to environmental pollution
Graphene (Gr) and hexagonal boron nitride (h-BN), as the two most prototypical twodimensional (2D) materials, have been considered in the past decade to be ideal ultrathin coatings to protect metallic components working in various aggressive environments under the influence of many factors without changing the physical properties of the protected metallic substrate
Density-functional theory is an accurate and efficient theoretical tool for disentangling the microscopic mechanisms involved in the complex couplings in corrosion processes is powerful in quantitatively assessing the service performance of 2D coatings and can help propose promising methods to optimize the anticorrosion 2D coatings
Summary
The excellent corrosion and oxidation resistances of the Gr coating, due to its high air stability and excellent impermeability, have been extensively studied. Compared with the Gr/Cu sample, the h-BN/Cu sample shows much less color change and less corroded areas, implying that h-BN rather than Gr is an effective long-term corrosion barrier for Cu. The Tafel plots and Bode plots of Gr coated Cu and h-BN-coated Cu both give out the same information as that from their optical microscopy images. During a long-term exposure to an oxidizing environment, when the exposed metal substrate areas are largely/fully passivated, the corrosion resistance of the h-BN coating will outperform that of the Gr coating as expected [47,52]. Gr coating in the high-temperature oxidative condition (≥250 ◦ C) and long-term working period (≥9 h) [52]
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