Experimental, DFT, and molecular simulation insights into the corrosion inhibition performance of SrCuP 2 O 7 on carbon steel in HCl

Strontium copper diphosphate SrCuP2O7 was synthesized by a conventional high-temperature solid-state reaction and investigated as a corrosion inhibitor for C35E carbon steel in 1.0 M HCl at 303 K. The phase purity and crystal structure of the synthesized material were confirmed by X-ray diffraction (XRD), while its vibrational properties were characterized by Raman and infrared spectroscopy. The corrosion inhibition performance was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), complemented by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX). Density functional theory (DFT), molecular dynamics (MD), and Monte Carlo (MC) simulations were further employed to investigate the adsorption behavior and inhibition mechanism. SrCuP2O7 exhibited a maximum inhibition efficiency of 96.4% at 10−3 M, with the polarization results confirming its mixed-type inhibition behavior with predominant anodic inhibition. The Nyquist plots showed increasing semicircle diameters with inhibitor concentration, indicating enhanced charge-transfer resistance, while the corrosion process remained controlled by charge transfer without a change in the corrosion mechanism. The adsorption process followed the Langmuir isotherm, indicating monolayer adsorption on the steel surface. The inhibition mechanism is mainly attributed to the adsorption of SrCuP2O7 species on the steel surface, which hinders charge transfer at the metal/solution interface and suppresses corrosion reactions. SEM/EDX observations further supported the formation of a protective film. The theoretical calculations revealed favorable adsorption of SrCuP2O7 on the Fe(110) surface, consistent with the experimental results. These findings demonstrate the effective corrosion protection provided by SrCuP2O7 for C35E carbon steel in acidic medium.