Moradi M, Rezaei M, Marashi P, Rainforth WM. Smart Doped Polyaniline Coating for Wireless Anodic Protection of AISI 304 Stainless Steel in a Corrosive Medium Containing Sulfate and Chloride Ions: Electrochemical and DFT Evaluations.
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024;
40:13303-13318. [PMID:
38865082 DOI:
10.1021/acs.langmuir.4c01718]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2024]
Abstract
Polyaniline (PANI) coatings have the capability of in situ anodic protection of stainless steels (SSs). However, these coatings have a high degradation rate in sulfuric acid. Also, the protection of SSs in a medium contaminated with chloride ions is an unsolved challenge. Therefore, the present work aims to modify the electrodeposited PANI coating with different dopants to find the optimal coating for the anodic protection of 304 SS in chloride-contaminated sulfuric acid. Thus, CH3COO-, HSO4-, NO3-, H2PO4-, and NaSO4- were doped electrochemically in PANI to determine the most effective corrosion depressor. Density functional theory (DF)T calculations determined that the lowest Gibbs free energy (more spontaneous doping) is for HSO4- doping by 24 kcal/mol. The band gap energy is <0.5 eV for the PANI/H2SO4 coating, indicating the very high conductivity of this coating. Monte Carlo simulation revealed that the highest deformation energy is related to PANI/H2SO4 at 1877 kcal/mol (stronger adsorption). Mott-Schottky and energy-dispersive spectroscopy (EDS) results showed that PANI doped with sulfuric acid creates a p-type semiconductor (Ni-rich), while the rest of the dopants lead to the formation of an n-type semiconductor passive film (Fe/Cr-rich). Despite the relatively low corrosion resistance of PANI/H2SO4 in the early days, its resistance improved over time by more than 1 order of magnitude. Therefore, this seems to be a more favorable option for long-term anodic protection. Thus, in this work, the corrosion behavior of the passive film formed at the interface of PANI and SS was comprehensively evaluated.
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