Dual-Layer Composite Polyurethane Coating Integrating Corrosion Inhibition and Self-Healing for Durable Corrosion Protection

Organic coatings tend to lose their corrosion protection during service in a marine environment. In this study, a dual-layer composite polyurethane (c-PU) coating consisting of a superhydrophobic bottom layer and a self-healing polyurethane surface layer was designed for durable corrosion protection. The bottom layer was constructed by bonding praseodymium-loaded polyaniline-modified hexagonal boron nitride (Pr3+@PANI@h-BN) nanoparticles with epoxy resin. The surface layer was prepared by the synthesized self-healing polyurethane with dynamically reversible Diels–Alder covalent bonds. Tafel polarization curve tests demonstrated that the c-PU coating exhibited significantly improved corrosion resistance, with a corrosion current density as low as 95.17 pA/cm2. The electrochemical impedance spectroscopy revealed that the low-frequency impedance modulus of the pristine c-PU coating was 8.9 × 108 Ω·cm2, which decreased to 9.9 × 104 Ω·cm2 after scratching. Upon thermal heating at 130 °C for 10 min, the value returned to 8.7 × 108 Ω·cm2, indicating complete restoration of its barrier properties against corrosion media. In summary, the bottom layer provides corrosion inhibition through active corrosion inhibition, passivation, and a physical barrier, while the surface layer maintains integrity via its self-healing ability. The synergy of the two layers enables the coating to deliver long-term protective performance in harsh corrosive environments, offering a promising strategy for extending the service life of marine steel structures.