Diatom-inspired pH-responsive MOF coatings for active corrosion protection and sustained drag reduction in dynamic marine environments

The development of multifunctional coatings that simultaneously address corrosion resistance and hydrodynamic drag reduction is essential for the next generation of amphibious platforms such as electric vertical take-off and landing aircraft (eVTOLs), which frequently operate in harsh marine environments. Lightweight aluminum alloys, though widely used in eVTOL components due to their high strength-to-weight ratio, are inherently prone to localized corrosion and surface drag when exposed to saltwater immersion and dynamic fluid flow. To overcome these dual limitations, we present a biomimetic bifunctional coating inspired by the hierarchical silicification of diatom frustules. The system integrates a pH-responsive cobalt-based metal–organic framework (Co-MOF) loaded with benzotriazole (BTA), encapsulated within a layered silica shell and further modified with a fluorine-free, low-surface-energy HDTMS layer. This composite enables both environmentally triggered corrosion inhibitor release and robust superhydrophobicity (contact angle: 163.3° ± 1.2°, sliding angle: 2.3°). The coating retains a high impedance modulus (>10 9  Ω·cm 2 ) after 30 days of immersion in 3.5 wt% NaCl, with BTA release efficiency reaching 85 % under acidic conditions. Drag-reduction performance remains stable over 40 cycles, achieving a maximum drag reduction of 31.5 %. Meanwhile, after undergoing 10 abrasion cycles, the coating still maintained a contact angle of 147°, demonstrating hydrophobic properties. This work demonstrates a synergistic material platform tailored for eVTOL marine operations, offering a pathway to extend service life, reduce energy consumption, and support the advancement of low-altitude, low-carbon transportation technologies.