Computational and electrochemical studies of some amino acid compounds as corrosion inhibitors for mild steel in hydrochloric acid solution

The corrosion inhibition behaviour of four selected amino acid compounds, namely l-cysteine, l-histidine, l-tryptophan and l-serine on mild steel surface in deaerated 1 M HCl solution were studied electrochemically by Tafel polarization and electrochemical impedance spectroscopy methods and computationally by the quantum chemical calculation and molecular dynamics simulation. Electrochemical results show that these amino acid compounds inhibit the corrosion of mild steel in 1 M HCl solution significantly. The order of inhibition efficiency of these inhibitors follows the sequence: l-tryptophan > l-histidine > l-cysteine > l-serine. The quantum chemical calculations were performed to characterize the electronic parameters which are associated with inhibition efficiency. The molecular dynamics simulations were applied to find the equilibrium adsorption configurations and calculate the interaction energy between inhibitors and iron surface. Results obtained from Tafel and impedance methods are in good agreement. The electrochemical experimental results are supported by the theoretical data.