The shipping industry is vital to global trade. Unfortunately, this industry is negatively impacted on a large scale by biofouling, a process whereby unwanted organisms accumulate on submerged surfaces, massively affecting traveling speed and fuel consumption. Fortunately, antifouling coatings have been developed to combat this problem. This review summarizes the process of biofouling and briefly discusses the history of antifouling coating development. Moreover, eight major antifouling coatings are reviewed, including bionic microstructure, self-polishing, fouling and desorption, zwitterionic polymer, self-assembled thin-layer, liquid-smooth surface, conductive, and photocatalytic antifouling coatings. The technical principles, innovation, and advancement of each coating are expounded, and the relevant research progress is discussed. Finally, the remaining issues and challenges in antifouling coatings are discussed, along with their prospects.

Stainless steels (SSs) easily suffer localized corrosion damage, such as pitting corrosion, in mixed solutions of acetic acid and sodium chloride. Currently, few works have been focused on the early stages of the pitting corrosion (metastable pitting corrosion) process of SSs in a chloride-HAc mixture solution. In this work, the effects of acetic acid (HAc) and its concentration on metastable pitting corrosion and the uniform corrosion of 304 SS in 0.6 mol/L NaCl solution were investigated by a slow-scanning potentiodynamic polarization test, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results show that the uniform corrosion rate of 304 SS increases after HAc addition but, with an increase in HAc concentration, the corrosion rate decreases. In the presence of HAc, the metastable pitting potential (E_m) and stable pitting potential (E_b) move negatively, but the number of metastable pits notably decreases. HAc has a promoting action on the growth rate of the metastable pits and facilitates the transition from metastable pits to stable pits. The influence of HAc is related to a decrease in solution pH and the chemical adsorption of HAc.

The degradation processes of two self-polishing antifouling coatings containing copper-based agents (CuSCN and Cu₂O) in 3.5% NaCl solution and the protection effect of the coating systems were studied by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM/EDS) methods. The results demonstrate that after immersion for 1525 d at room temperature, the two coating systems still have very good protection property for the 5083 Al alloy substrate, manifesting by the high value of the low-frequency impedance. Alternate high and low temperature immersion test (45 °C 12 h + 25 °C 12 h) leads to serious damage to the antifouling topcoat, and the failure is mainly manifested by many micro-pores and micro-cracks. Because the CuSCN antifouling agent particle has bigger diameter and slightly higher solubility than that of Cu₂O agent, the micro-pores established after the agents dissolved and released during the hydrolysis process of the antifouling coating are relatively larger, which results in more decrease in the impedance and a worse protective property of the coating system for the substrate.