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Leveraging rare-earth elements as one of the eco-friendly candidates to protect alloy coatings, this study performed the europium functionalization of carbon nanotubes (Eu–CNT) for magnesium alloy protection in the 3.5% NaCl medium. The obtained composite material was characterized by various techniques to confirm its modified chemical structure. The europium ion was shown to be chelated by carbon nanotube functional groups as confirmed by infrared (IR) and Raman spectroscopies, and the polyamorphous character of CNT and europium phases was revealed by the X-ray diffraction study (XRD). The microstructure of the composite material was investigated by field emmision scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The cyclic voltammetry results showed that the composite material becomes stable after five redox cycles. The corrosion inhibition efficiency was shown to be 82% as compared to the epoxy coating. Also, the Eu–CNT composite coating acts as a mixed inhibitor, it controlled anodic as well as cathodic inhibition. Density functional theory (DFT) study results supported the experimental findings, suggesting that the Eu–CNT composite would effectively interact with various charged corrosive species in the solution phase. The findings of this study are anticipated to contribute new knowledge to design of functional coatings and energy storage materials based on rare-earth functionalized CNT. The cytotoxic effects of Eu–CNT composite material above the concentration of 150 μg mL−1 should be considered as well in further steps of its development as human exposure is inevitable. [ABSTRACT FROM AUTHOR]