Corrosion Inhibition of Stainless Steel Grade 202 by Combined Coatings of Banana Peel Powder, Polyaniline and CuO in Hydrochloric Acid Medium

Abstract Corrosion of steel in acidic media remains a major challenge in industrial applications, particularly for cost-effective alloys such as Stainless Steel (SS) Grade 202. This study aims to develop an environmentally friendly, low-cost, and efficient corrosion-inhibition system using banana peel powder (BPP) extract, polyaniline (PANI) and copper oxide (CuO), tested individually and in synergistic combinations. The BPP extract prepared through refluxing to isolate bioactive phytochemicals is responsible for adsorption on the SS surface. Moreover, CuO particles synthesized using chemical (sol-gel) and green synthesis methods, when combined with carbonized BPP, overcomes the degradation issue of BPP alone, demonstrating strong corrosion inhibitory activity of SS Grade 202 in 0.50 mol L⁻¹ HCl medium, as evidenced by mass loss measurements, open circuit potential measurements, electrochemical impedance spectroscopy and Tafel polarization. More importantly, BPP+PANI+CuO combined coating exhibits superior corrosion inhibitory performance, reflected by enhanced charge-transfer resistance, reduced corrosion current density, and more noble corrosion potential values. Scanning electron microscopic analysis confirms improved surface coverage and reduced pitting of the combined coating. Overall, synergistic interactions among BPP, PANI and CuO significantly enhances corrosion resistance of SS Grade 202 in HCl environments.