Research progress on the anticorrosive mechanism of the redox engine effect of polyaniline in epoxy resin coatings

Polyaniline (PANI) is a promising anti-corrosion material that can construct a dynamic electronic regulation system at the metal/coating interface and induce the formation of a dense passive film by virtue of its unique redox reversibility. However, pure PANI suffers from poor compatibility with resins, environmental sensitivity, and insufficient durability. In this review, the concept of "redox engine" effect is introduced, and the research progress of PANI-based anti-corrosion coatings is systematically reviewed. The dynamic redox conversion mechanism of PANI, as well as the thermodynamic and kinetic rules of electron transfer at the metal/PANI interface, are elaborated. The strategies for optimizing the "engine" intake and transmission devices to enhance electron transfer regulation are summarized, including acid doping, metal ion doping, ionic liquid doping, and carbon material compounding. Moreover, the research advances in multi-system synergistic protection are reviewed, covering metal oxide compounding, inorganic material compounding, pH-responsive system assembly, and biomimetic micro/nano structure design. Furthermore, the current bottlenecks of PANI-based coatings are pointed out, such as insufficient long-term self-healing ability and easy deactivation in alkaline environments. Future research directions are also prospected, which may provide theoretical references and research ideas for the development of intelligent and efficient PANI-based anti-corrosion coatings.