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The inhibition properties of the isopropanol extract of brown seaweed Cystoseira baccata (CBE), against corrosion of carbon steel in HCl 1M medium, was evaluated using the weight-loss method and electrochemical measurements. It was shown that the extract exhibit excellent performance as inhibitors and the inhibition efficiency increased with the concentration. The maximal value of inhibition efficiency is 86.5% obtained by the Tafel method at 700 mg/l at 298 K. The polarization curves indicate that the CBE acts as a mixed-type inhibitor. The results obtained by electrochemical impedance spectroscopy shows that the inhibitory action of this extract is based on the increase in the charge transfer resistance and the decrease in the double layer capacity. The temperature influence studied in the temperature range 298-328 K by weight-loss method shows that the inhibition efficiency decreases with increasing temperature for all concentrations of CBE. The adsorption and activation parameters allow us to suggest the physical adsorption of this inhibitor on the metal. The adsorption of the extract on the carbon steel follows Langmuir adsorption isotherm.

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To explore the potential of new ecological corrosion inhibitors, we investigated the mechanism of corrosion inhibition in carbon steel using Halopitys incurvus, an algal extract available in both crude and chromatographic fractions, in a 0.5 M H2SO4 medium. Various methods were employed, including gravimetry, electrochemical impedance spectroscopy, polarization curves, scanning electron microscopy (SEM) techniques, and molecular dynamics. The crude extract exhibited a high corrosion‐inhibiting potential, with a maximum inhibitory efficiency of 85.30% at 600 mg/L. The electrochemical results indicated mixed behavior of the crude extract. Furthermore, we found that the adsorption of the crude extract onto the metal surface followed the Langmuir isotherm pattern. The SEM study confirmed our proposition that extract molecules were adsorbed onto the carbon steel surface. Using the chromatographic fractionation protocol, we were able to distinguish four main fractions, and the most effective fractions reached an inhibitory efficiency value of 96.00% at 100 mg/L. The molecular dynamics simulation confirmed the experimental results.