Effect of 1H-Benzotriazole–CeO2 NPs Hybrid Inhibitors on the Corrosion Protection of Carbon Steel in Chloride Solutions

In this study, 1H-benzotriazole (1H-BTA) and cerium oxide (CeO2) nanoparticles were investigated as corrosion inhibitors for A1008 low carbon steel in 3.5% NaCl solution. Short-term immersion tests showed that CeO2 NPs achieved an inhibition efficiency of 73.35% at 0.3%, while 1H-BTA reached 74.13% at 2.5 mmol L−1. Remarkably, their combined use significantly enhanced corrosion protection, yielding an efficiency of 93.46% with 2.5 mmol L−1 1H-BTA and 0.2% CeO2 NPs. The 1H-BTA–CeO2 NPs hybrid inhibitors induced a positive shift in corrosion potential relative to the untreated steel, reflecting more anodic behavior, and simultaneously suppressed both anodic and cathodic reactions, consistent with a mixed inhibition mechanism. This was accompanied by a marked reduction in corrosion current density and a substantial improvement in corrosion resistance. Surface analysis revealed that the 1H-BTA–CeO2 NPs hybrid inhibitors produced a homogeneous, crack-free film enriched in Ce and N, confirming its strong barrier properties. During long-term immersion, the composite maintained a high inhibition efficiency of 92.90%, outperforming 1H-BTA (85.56%) and CeO2 NPs (45.09%), thereby highlighting the pronounced positive effect of the hybrid system. Thermodynamic analysis further indicated that the adsorption of CeO2 NPs, 1H-BTA, and the 1H-BTA–CeO2 hybrid on the carbon steel surface proceeds through a mixed physisorption–chemisorption mechanism.