Integrative Electrochemical and Quantum Chemical Evaluation of a Schiff Base Inhibitor for Acidic Corrosion of XC70 Steel

A Schiff base compound, designated as L3, was successfully synthesized and thoroughly analyzed through various characterization techniques, including Fourier-transform infrared (FT-IR) spectroscopy, and elemental composition analysis. Its corrosion inhibition properties for XC70 carbon steel in 1 M HCl solution were assessed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods. The investigation examined the impact of both L3 concentration and temperature on its performance. Results indicated a direct correlation between increased concentration and temperature and improved inhibition efficiency (IE%), which reached a maximum of 84% at 10–4 M. PDP measurements revealed that L3 functions as a mixed-type inhibitor, affecting both anodic and cathodic processes. EIS data demonstrated that rising L3 concentrations enhanced the charge transfer resistance (Rct) from 104.3 to 251.2 Ω cm2, while reducing the double-layer capacitance (Cdl) from 108.6 to 63.64 µF cm–2, suggesting strong inhibitor adsorption at the metal-solution interface. Thermodynamic parameters such as $$\Delta G_{{{\text{ads}}}}^{^\circ }$$ , ΔHa, Ea, and ΔSa were calculated to clarify the inhibition mechanism, indicating that L3 adsorption occurs via chemisorption. Furthermore, the adsorption behavior followed the Langmuir isotherm model. Finally, quantum chemical analyses were carried out to interpret how the electronic structure of L3 influences its corrosion inhibition performance.