This study investigates the corrosion inhibition performance of Cola lepidotaleaf extract on mild steel in 1 M Hydrochloric acid (HCl), aiming to develop a sustainable green inhibitor for acid-based industrial processes. Phytochemical screening identified bioactive constituents such as alkaloids, flavonoids, tannins, saponins, and phenols compounds known for their surface-active and metal-chelating capabilities. Fourier Transform Infrared Spectroscopy(FTIR) spectra confirmed that these compounds adsorb onto the steel surface through O–H, N–H, and C=O functional groups, forming Fe–O and Fe–N linkages that generate a stable protective film. Electrochemical analyses revealed a substantial reduction in corrosion current density from 5.87 × 10⁻³ A (blank) to 3.42 × 10⁻³ A at 8 g·L⁻¹ with inhibition efficiency exceeding 70%. Nyquist and Bode plots confirmed charge-transfer resistance enhancement and double-layer capacitance reduction due to surface film formation. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM/EDS) analyses corroborated these findings, showing a smoother surface with reduced Fe and Cl peaks and enrichment in carbon and oxygen, indicating formation of an adherent organic barrier. Overall, Cola lepidota leaf extract provides effective, concentration-dependent corrosion inhibition via adsorption of phytochemical constituents, offering an eco-friendly and renewable alternative to toxic synthetic inhibitors for mild steel protection in acidic media.
