Abstract
The corrosion inhibition performance of 5-Carboxypentyl Triphenylphosphonium Bromide (5-CPTPPB) for mild steel (MS) in 0.5 M H2SO4 solution was investigated using electrochemical, surface and computational methods. Galvanostatic polarisation and EIS show that at an optimal concentration of 10-2 M, 5-CPTPPB exhibited an inhibition efficiency above 97%, functioning as a mixed-type inhibitor that effectively suppressed both anodic and cathodic reactions. Thermodynamic studies show that the adsorption of inhibitor on the metal surface follows the Langmuir adsorption isotherm. Surface characterization techniques, including atomic force microscopy (AFM), and scanning electron microscopy (SEM) confirmed the development of 5-CPTPPB barrier layer on the metal surface. Fukui function analysis showed that protonation enhanced the electrophilic character of key atomic sites, supporting dual donor-acceptor reactivity. Molecular dynamics (MD) simulations further validated these findings showing highly negative interaction and binding energies, confirming spontaneous and stable adsorption. Additionally, Non-Covalent Interaction (NCI) analysis highlighted mixed physisorption-chemisorption mechanism. Collectively, the integrated experimental and theoretical results establish 5-CPTPPB as a highly effective, stable, and environmentally sustainable corrosion inhibitor for MS under aggressive acidic conditions.