Enhanced corrosion inhibition of aniline derivatives electropolymerized coatings on copper: Preparation, characterization and mechanism modeling

Nanostructured polyaniline (PANi), poly(N-ethylaniline) (PNEA) and their molybdate-doped coatings (PANi-Mo and PNEA-Mo) were electropolymerized on passivated copper surface via voltammetric cycles in oxalic acid solution. The coating structures were featured by morphological observation, attenuated total reflectance infrared spectra (ATR-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS); besides, anticorrosive performance of coatings was investigated for copper in 0.5 M H2SO4 solution through electrochemical and topographical measurements. ATR-IR and XRD results documented the occurrence of polymerization over copper surface, while the morphologies implied that the presence of ethyl and molybdate generated the extra increment in coating thickness. Owing to physical barrier of substituent and in-situ dissolving of molybdate, the corrosion of coated specimens was highly suppressed in H2SO4 solution. The protective effect of coatings followed the sequence of PNEA-Mo > PANi-Mo > PNEA > PANi with an inverse trend in porosity index. XPS analyses revealed that repeat units of polymer were in mixed state with predominantly oxidative type, which were inclined to parallelly deposit on copper surface with a strong anchoring strength. Molecular dynamics simulations well supported the configuration and forceful adhesion of polymers on Cu (1 1 1) plane, and indicated the favorable compatibility between polymer and dopant.