Comparative study on the electrodeposition and corrosion resistance of polypyrrole doped by phosphotungstate and benzalkonium chloride

Polypyrrole (PPy) coating and PPy composite coatings were successfully electrodeposited on mild steel in the electrolytes of oxalic acid in the absence and presence of dopants using cyclic voltammetry. Two types of doping ions were employed: phosphotungstate (PW₁₂O₄₀^3-) and benzalkonium chloride (BAC). Corrosion-resistant performances of the coatings in 0.1 M HCl showed that PPy composite coatings in the presence of phosphotungstic acid and BAC exhibit more effective protection for iron in comparison with PPy formed in 0.3 M oxalic acid, and corrosion resistance of PPy-BAC is better than PPy-PW₁₂ even though PPy-PW₁₂ shows nobler open-circuit potential for a longer period of time than PPy-BAC. Impedance measurements show that, after immersion of 12 h in 0.1 M HCl, the polarization resistances of PPy-PW₁₂ and PPy-BAC coatings reach 1860 and 3110 ω cm², respectively, compared to 640 ω cm² of PPy deposited from 0.3 M oxalic acid.