Polyaniline-based hybrid coatings for corrosion protection: Breakthroughs in nanocomposite design, self-healing, and corrosion sensing

Polyaniline (PANI), a conductive polymer renowned for its unique electrochemical properties, has recently emerged as a promising corrosion-protective material owing to its active passivation capability, robust barrier effects, and intelligent, stimulus-responsive functionalities. This review examines recent advancements in PANI-based hybrid coating systems and their applications for corrosion protection across diverse metallic substrates. Emphasis is placed on novel hybrid architectures, including composites of PANI with metal oxides, two-dimensional materials (graphene, MXenes), and functional nanohybrids, which exhibit exceptional corrosion resistance, high impedance, and autonomous self-healing properties. Comprehensive characterization approaches, encompassing electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and nanoscale imaging methods, are systematically integrated to elucidate corrosion inhibition mechanisms, barrier performance, and interfacial phenomena governing coating effectiveness. Special attention is devoted to “smart” hybrid coatings where coordination-engineered PANI systems enable functionalities such as pH-responsive inhibitor release, fluorescence-based corrosion sensing, and photothermal self-healing, demonstrating multifunctional protection capabilities. Practical applications in aggressive industrial, marine, and automotive environments demonstrate PANI's significant potential to enhance structural longevity and reduce maintenance costs. Despite remarkable advancements, challenges related to long-term durability, environmental sustainability of dopants, cost efficiency, and scalability remain. The review concludes by highlighting strategic research directions toward sustainable multifunctional hybrid coatings and integrated sensor technologies, positioning PANI-based materials as key candidates in next-generation anticorrosion coating solutions. • PANI's redox chemistry enables active passivation and barrier reinforcement. • Hybrid systems with 2D materials and metal oxides deliver synergistic protection. • Smart coatings achieve self-healing, inhibitor release, and corrosion sensing. • Substrate-tailored strategies address iron, aluminum, and copper corrosion. • Bio-based dopants and scalable synthesis enable sustainable coating solutions.