Experimental and DFT Studies on the Two Imidazolium-based Ionic Liquids as Green Corrosion Inhibitors for A516-GR70 Carbon Steel in 3.5 wt.% NaCl Solution Saturated with CO2

1-Dodecyl-3-methylimidazolium chloride (DDMIC) and 1-(Naphtymethyl)-3-methylimidazolium chloride (NMIC) were synthesized, and their adsorption effects on A516-Gr70 steel were investigated as a green corrosion inhibitor in 3.5 wt.% NaCl solution saturated with CO2 at 25 °C. Potentiodynamic polarization (PDP), Scanning Kelvin probe (SKP), and electrochemical impedance spectroscopy (EIS) techniques were used to study the inhibition properties of these compounds in different concentrations. The main advantages of the two studied inhibitors, i.e., DDMIC and NMIC, are environment friendly; moreover, the inhibition performance of DDMIC is excellent, and it can reach 97% protection performance in a sweet corrosion environment. SKP studied the effects of these inhibitors on the Volta potential of the carbon steel surface. SKP analysis revealed that the trend of metal surface coverage by DDMIC can be traced via Volta’s potential results. Based on SKP results, the real work function of metal surface atoms was calculated. Quantum chemical parameters of inhibitor molecules were studied by integrating density functional theory (DFT) and SKP methods. The integration results described the electron transfer mechanism during the adsorption process. Ultimately, SKP and DFT results revealed that the aromatic ring of NMIC affected its adsorption on the metal surface.