Corrosion inhibition and discharge performance of thiourea derivatives as anode additives for alkaline aluminum-air batteries: Experimental and computational insights

The development of efficient anode additives is critical to enhance the stability and utilization efficiency of aluminum-air batteries in alkaline electrolytes. In this study, the corrosion inhibition and discharge behavior of four thiourea derivatives, allylthiourea (ATHU), diphenylthiourea (DPTU), methylthiourea (MTHU), and thiourea (THU), are systematically investigated in a 4 M KOH solution. Electrochemical measurements (OCP, LPR, EIS, and PDP) are complemented by weight-loss analysis, galvanostatic discharge tests, and surface characterization (SEM/EDS and 3D optical profilometry). The results show that all four inhibitors reduce the corrosion rate of aluminum, with DPTU exhibiting the highest inhibition efficiency (81.5% from EIS), followed by ATHU and MTHU, while THU is least effective in static inhibition tests. Surface analyses confirm the formation of protective films that suppress pitting and reduce roughness. Computational studies further explain the observed trends, in which DFT reveals that DPTU has the lowest HOMO-LUMO gap and the strongest donor sites (S and N atoms with π-delocalization), favoring adsorption. MD simulations confirm the highest binding energy for DPTU (100 kcal mol⁻¹) and the lowest diffusivity of corrosive species through its adsorbed film. Interestingly, galvanostatic discharge tests indicate that THU, despite its weaker inhibition, achieves the highest anodic utilization (61.1%) and energy density (2703.6 Wh·kg⁻¹).