Experimental and theoretical insights into the inhibitory capabilities of polythiophene and polypyrrole molecules for protecting mild steel from corrosion in sulfuric acid

Abstract

solution was systematically investigated using potentiodynamic polarization, potentiodynamic anodic polarization, electrochemical impedance spectroscopy (EIS), and weight loss measurements. The novelty of this study lies in its integrated approach, which correlates experimental chemical and electrochemical analyses with quantum chemical calculations and Monte Carlo simulations to provide a comprehensive understanding of the inhibition mechanism. The results demonstrate that both PT and PPy act as mixed-type inhibitors, significantly reducing corrosion through adsorption onto the MSt surface in accordance with the Langmuir adsorption isotherm. The inhibition efficiency increases with increasing inhibitor concentration, while it decreases with rising temperature, suggesting that the adsorption process is predominantly physical in nature. Polarization measurements further confirm that PT and PPy behave as mixed-type inhibitors and exhibit pitting inhibition behavior, as evidenced by the positive (noble) shift in the pitting corrosion potential with increasing inhibitor concentration. Thermodynamic parameters associated with activation and adsorption processes were determined and discussed in detail. In addition, a comparative study of PT and PPy adsorption on the Fe (110) surface was conducted using quantum chemical descriptors and Monte Carlo simulations. The combined electronic structure analysis and adsorption results consistently indicate that PPy forms a more stable and protective adsorbed layer, in excellent agreement with experimental findings, thereby identifying it as the more effective polymeric inhibitor for mild steel corrosion protection.