A Green Shield for Copper: Corrosion Inhibition by Fennel ( <i>Foeniculum vulgare</i> ) Seed Extract Revealed through Experiments and Modeling

The development of nontoxic, biodegradable corrosion inhibitors is crucial for sustainable industrial practices. While plant extracts show promise, their mechanistic action on copper in acidic media remains insufficiently explored. In this study, the high anticorrosion performance of fennel (<i>Foeniculum vulgare</i>) seed extract (FVE) on copper in 0.5 M H₂SO₄ was investigated. Electrochemical analyses (open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP)) demonstrate that FVE acts as a mixed-type inhibitor, achieving 93% efficiency at 500 mg/L by suppressing both anodic dissolution and cathodic reactions. The existence of a protective adsorbed film is evidenced by surface characterization using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Theoretical density functional theory (DFT) calculations further corroborate FVE's adsorption mechanism, indicating strong interaction energies and electron-donating ability from key phytocompounds. The integrated theoretical and experimental findings support FVE as a feasible and eco-sustainable candidate for traditional corrosion inhibitors.