A cautionary note on graphene anti-corrosion coatings

Ångström-Scale, Atomically Thin 2D Materials for Corrosion Mitigation and Passivation

“…A small opening in the graphene coating can expose a small underlying metallic (anodic) area to the larger cathodic area. When the ratio between the cathodic (graphene) and anodic (metal) areas of two dissimilar materials becomes high, accelerated localized pitting/galvanic corrosion of the anode exacerbates the material degradation (Figure 9c,d) [137]. Therefore, an imperfect graphene coating can unintentionally worsen the corrosion scenario, whether is in the intrinsic or composite form [138].…”

“…Graphene galvanically couples Cu and oxygen that increases corrosion, whereas, hBN shows no galvanic coupling; (c) pitting corrosion due to a galvanic coupling of two different metal featuring a large ratio of cathodic to the anodic area corresponding to higher corrosion current; (d) and (e) Corrosive species attacking and propagating through grain boundaries of anodic metal (exposed due to scratch) and reducing material strength rapidly. Adapted with permission from ref [137]…”

Tortuosity but not Percolation: Design of Graphene Nanocomposite Coatings for the Extended Corrosion Protection of Aluminum Alloys

“…While the value of the electrode potential of graphene, or for that matter, graphite, varies as a function of the surface chemistry, the reported value of +0.150 V (pure graphite versus SCE) 17 is substantially higher as compared to pure aluminum (-0.76 V versus SCE; corrosion potential of Al 7075-T6 is -0.765 V versus SCE); 18 consequently, galvanic corrosion of the latter is possible upon direct coupling. 19 Zettl and coworkers have shown that the corrosion of Cu is initially diminished by the presence of graphene layers deposited directly onto the substrates owing to the impermeability of graphene. 20 However, in the presence of defects, the permeated electrolyte establishes a corrosion cell between the graphene layer and the underlying copper substrate, bringing about accelerated galvanic corrosion of the underlying metal.…”

Corrosion Behavior of Zinc–Nickel and Graphene Layered Structures on Steel Substrates

“…Coatings based on graphene have shown promising anti‐corrosion properties . However, the formation of defects and cracks in the structure of the coatings can accelerate corrosion because graphene is cathodic to several metals …”