Integrating Electrochemical and Computational Studies to Elucidate the Corrosion Inhibition Mechanism of 4‐Nitrobenzyl Triphenylphosphonium Bromide on Mild Steel in Acidic Environment

The corrosion inhibition performance of (4‐nitrobenzyl) triphenylphosphonium bromide (NBTPPB) on mild steel in 0.5 M H 2 SO 4 was systematically evaluated through electrochemical, surface, and computational analyses. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) revealed that NBTPPB acts as an efficient mixed‐type inhibitor, significantly increasing charge transfer resistance (Rct) and reducing double‐layer capacitance (Cdl), consistent with Langmuir adsorption isotherm behavior. Surface characterization by SEM, EDX, and Atomic Force Microscopy (AFM) confirmed smoother and less damaged morphologies in the presence of NBTPPB, demonstrating the formation of a stable protective film. Density functional theory (DFT) calculations provided complementary insight, with a relatively small HOMO–LUMO gap (2.27 eV), high dipole moment (14 Debye), low global hardness, and high softness, all indicative of strong electronic reactivity. The calculated number of transferred electrons (ΔN inh ≈ 1.5) confirmed effective charge transfer to the steel surface, while binding energy and molecular dynamics (MD) simulations revealed spontaneous and stable adsorption for both neutral and protonated species, with protonation enhancing adsorption strength in acidic conditions. Collectively, the results establish NBTPPB as a promising and environmentally viable corrosion inhibitor, with performance primarily governed by chemisorption reinforced by charge transfer interactions. This work also highlights the potential of phosphonium‐based compounds as a platform for developing next‐generation corrosion inhibitors.