Amino-Functionalized Graphene-Zinc Coordination Interface-Induced Intergranular Corrosion for Superior Cathodic Protection of Low-Zinc Epoxy Coating.

Graphene is an ideal reinforcement for enhancing the corrosion resistance of low-zinc epoxy coatings owing to its high specific surface area, excellent conductivity, and barrier properties. However, the low electron transfer efficiency in such coating often leads to uniform corrosion of zinc powder with corrosion products enveloping its surface, causing premature failure and low zinc utilization. Herein, amino-functionalized graphene (Gr-NH2) was synthesized to prepare Gr-NH2 reinforced low-zinc epoxy coatings (Gr-NH2/ZEC, 40 wt % zinc), where edge-grafted -NH2 groups were covalently bonded to graphene and C-N-Zn electron pathways were established between graphene and zinc fillers. The enhanced Gr-NH2/Zn interfaces promote interfacial electron transfer, redirecting zinc corrosion from uniform corrosion to preferential intergranular corrosion, which continually fractures zinc particles and exposes fresh active surfaces. As a result, Gr-NH2/ZEC shows a high initial |Z|f = 0.01 value of 1.16 × 108 Ω at 6 h immersion, which is approximately 5.4 times that of GO/ZEC. After 28 days of immersion corrosion, the |Z|f = 0.01 value remained 8.88 × 107 Ω, which is very close to its initial value and still higher than that of GO/ZEC. Meanwhile, the enhanced intergranular corrosion also enables multiple reactivations of cathodic protection, thereby leading to a remarkable increase of zinc utilization efficiency from 9% to 20.5%. This interfacial engineering strategy provides a promising route for enhancing the cathodic protection performance of low-zinc epoxy coatings.