Solar Absorption and Corrosion Resistance of Polyurethane/Carbon Nanotube/Medium-Entropy Oxide Ultra-Black Coatings for Marine Applications

To address the issue of substrate corrosion susceptibility in marine environments characterized by high salinity and humidity, this study designed and fabricated a photothermal anticorrosion composite coating. Polyurethane (PU) was used as the film-forming binder with carbon nanotubes (CNTs) and (Mn 0.25 Cu 0.25 Fe 0.25 Co 0.25 ) 3 O 4 medium-entropy oxides (MEOs) incorporated into the coating system. The coating showed a high absorptivity of more than 99% in the wavelength range of 400–2000 nm. The excellent light absorption performance also improves the photothermal conversion efficiency, and the coating can be heated to 90 °C within 40 s under one sun intensity. Electrochemical impedance spectroscopy tests revealed that the resistance of the 30 wt % MEOs sample decreased from 10.24735 × 10 9 Ω/cm 2 to 9.22297 × 10 9 Ω/cm 2 after 30 days immersion, and the corrosion resistance was 4 orders of magnitude higher than that of the pure PU coating. This study presents a coating that integrates efficient photothermal conversion and long-term anticorrosion performance, providing a feasible strategy for the development of comprehensive properties coatings in the marine engineering field.