Sustainable additives to mitigate the self-corrosion of aluminium metal in alkaline solution: Electrochemical and theoretical investigations

This paper examines the effectiveness of three environmentally sustainable molecules, namely sodium citrate hydrate (SC), sodium octanoate (SO), and sodium benzoate (SB), in reducing the corrosion of high-purity aluminum in an alkaline medium (1 M NaOH). The molecules were tested using electrochemical experiments, including open circuit potential (OCP), linear polarization resistance (LPR), and potentiodynamic polarization (PDP), at concentrations of 0.5 %, 5 %, and 10 %. A comprehensive computational study was also conducted using density functional theory (DFT), molecular dynamics (MD), and Monte Carlo (MC) simulations. The electrochemical results showed that SO exhibited promising inhibition efficiency at a concentration of 10 %, while SB and SC performed almost equally with lower efficiency. The computational results aligned well with the experimental findings, ranking the molecules as SO > SB > SC. Furthermore, the detailed inhibition mechanism at the atomic level was explored in terms of the structure-property relationship of the organic molecules and their interactions with aluminum surface. The inhibitors SC, SO, and SB had energy gap values of 4.259, 3.577, and 3.708 eV, respectively, with SO showing the lowest energy gap and highest binding energy indicating strong interaction with Al surface. In addition, the inhibitors reduced H₂O and OH⁻ diffusion by 74.2 % and 66.4 %, respectively. The performance of SO in all cases indicates potential for further research and development to enhance corrosion protection strategies, contributing to better protection of aluminum in alkaline media, which is vital in the commercialization of aluminum-air alkaline battery.