Integrated electrochemical and quantum chemical evaluation of 1-phenylimidazole for carbon steel corrosion inhibition in HCl solution

Purpose This study aims to investigate the effectiveness of 1-phenylimidazole as a corrosion inhibitor for carbon steel in 1 M HCl solution, aiming to understand how concentration, temperature and molecular properties influence inhibition efficiency (IE). Design/methodology/approach Corrosion performance was evaluated using hydrogen evolution studies (303–333 K), electrochemical techniques, including electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) and quantum chemical calculations. Thermodynamic and kinetic parameters of the adsorption process were also determined. Findings IE increased with inhibitor concentration, reaching 72.0% with 0.8 g/L of 1-phenylimidazole at 303 K but decreased with rising temperature to 61.7 % at 333K for hydrogen evolution measurements. The trend of EIS and PDP validated the hydrogen evolution results, showing maximum inhibition efficiencies at 0.8 g/L of 1-phenylimidazole. Thermodynamic analysis showed that ΔH and ΔS are positive, indicating endothermic and spontaneous adsorption, Gads were negative and ranged between −5.5 and −1.9 kJ/mol, while Ea trends supported a physical surface adsorption mechanism. Quantum chemical analyses indicated a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 4.858 eV, high softness (0.411 eV−1), strong π–π* conjugation and significant electron delocalization, which facilitated strong adsorption of 1-phenylimidazole on steel. Originality/value This work combines experimental and theoretical approaches to demonstrate that 1-phenylimidazole is a moderately to highly effective corrosion inhibitor within the class of azole-based compounds, highlighting its molecular electronic features, p-conjugation, orbital delocalization and electron-rich regions as the primary drivers of adsorption. This integrated analysis provides new insights into the design of efficient inhibitors for acidic environments.