Unraveling the Inhibition of Copper Corrosion Kinetics by 4-aminoindazole in 3.5 wt% NaCl Solution: From In Situ Electrochemical Visualization to Atomic-Scale Adsorption Mechanisms

The effectiveness of organic inhibitors in mitigating chloride-induced copper corrosion is frequently constrained by insufficient understanding of the formation mechanism of protective adsorption films and their regulatory role in corrosion kinetics. In this work, the inhibition mechanism of 4-aminoindazole (4-AI) on copper in 3.5 wt% NaCl solution was systematically investigated via integrated in situ optical microscopy observation during potentiodynamic polarization (in situ electrochemical OM), theoretical calculations, and atomic-scale simulations. In-situ electrochemical OM results demonstrate that 4-AI effectively suppresses the initiation and propagation of grain boundary corrosion, increases interfacial charge transfer resistance, and markedly lowers the anodic current density. Electrochemical tests confirm that 0.8 mM 4-AI achieves superior immediate inhibition efficiency (94.4%) and outstanding long-term protective performance (99.7%). Surface characterization results verify the formation of a uniform 4-AI protective adsorption film with a thickness of 20 nm. The underlying mechanism involves chemisorption via Cu–N coordination bonds, with the N atoms acting as key active sites. 4-AI molecules adopt both parallel and vertical adsorption configurations on the copper surface, with the parallel mode being energetically favorable (adsorption energy E ads = –1.74 eV) and enabling the spontaneous assembly of a dense molecular film.