Mechanistic advances in graphene-based nanofiller epoxy coatings for corrosion protection of reinforcing steel: Performance and practical outlook

This review explores the use of graphene-based nanofillers to enhance the corrosion resistance of epoxy-coated steel. While epoxy coatings are widely applied, their inherent defects allow water and corrosive ions to penetrate. Graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), offer barrier properties but may also promote micro-galvanic corrosion due to agglomeration. This paper critically assesses the corrosion performance, and the corresponding mechanisms of epoxy coatings modified with G, GO, and rGO based on 51 published literature sources. The role of controlling mechanisms on the corrosion resistance efficiency are examined, including optimal nanofiller loading, surface functionalization, hybrid nanofiller coatings, and filler orientation within the epoxy matrix. Two categorizations of chloride exposure durations ≤24 h and >24 h on the corrosion resistance efficiency of epoxy coatings modified with G, GO, and rGO are reviewed. The inclusion of G-based nanofillers into epoxy coatings significantly enhances corrosion resistance in chloride-rich environments for both short-term (≤24 h) and long-term (>24 h) studies compared to a neat epoxy coating. Compared to neat epoxy, G-based epoxy coatings demonstrate superior barrier properties, with several studies reporting protection efficiencies exceeding 99 % under both short- and long-term chloride exposure. Despite this high initial corrosion efficiency, some coatings exhibited elevated delamination index ( DI ) values, indicating potential long-term interfacial degradation. In contrast, coatings incorporating oriented or functionalized G-based fillers demonstrated significantly lower DI values, suggesting more stable interfacial adhesion, in turn underscoring the complex interplay between initial barrier performance and long-term durability. These improvements are primarily attributed to enhanced impermeability, suppressed electrochemical activity, and optimized nanofiller dispersion. Among the synthesis methods reviewed, in situ polymerization ensures better structural uniformity and bonding, while optimized solution mixing offers a scalable, cost-effective option. While common techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet–visible spectroscopy (UV–vis), and Fourier transform infrared spectroscopy (FTIR) are used to assess G dispersion in epoxy, each presents limitations—including sample artifacts, shallow probing depth, and resolution constraints—emphasizing the value of a complementary, multiscale approach for reliable characterization. • Adding G, GO, and rGO -to epoxy coatings enhances corrosion resistance beyond 99% compared to neat epoxy in chloride exposure • High initial corrosion resistance efficiency does not necessarily guarantee long-term protection • Key corrosion resistance factors: optimal G content, functionalization, G orientation, and hybrid nanocomposites • In-situ polymerization is a suitable technique for synthesizing denser, well-dispersed coatings with low porosity and strong barriers