Theoretical and electrochemical investigation of citrus limon peel essential oil as green corrosion inhibitor for mild steel in 1 M HCl

In this potential study, we investigate the performance of three essential oils extracts (EO-A, EO-B, and EO-F) derived from Citrus limon peel collected in Agadir, Beni Mellal, and Fes, Morocco, as some green corrosion inhibitors to protect mild steel electrode in 1 M hydrochloric acid medium. The investigated inhibitors were tested using electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation (PDP), Bode measurements, scanning electron microscope (SEM), and energy dispersive X ray spectroscopy (EDS). The inhibition efficiencies increased with increasing concentration, and reach a maximum of 81.45 % (EO-A), 84.15 % (EO-B), and 83.62 % (EO-F), respectively. Different investigated inhibitors acted as mixed-type inhibitors by suppressing both anodic and cathodic reactions. SEM and EDS analysis confirmed the formation of a protective film on the steel surface. Complementary, the density functional theory (DFT) calculations identified γ-terpinene as the most chemically reactive constituent, supporting its key role in adsorption and inhibition. These findings highlight the potential of Citrus limon essential oils as eco-friendly corrosion inhibitors for industrial applications.