Corrosion behavior of plasma electrolysis layer cross-linked with a conductive polymer coating

Abstract

Tackling corrosion issues by oxide coatings has been one of the key research issues in valve metals, but these oxides are chemically vulnerable to a degradative hydration process in an aggressive environment. In this work, we highlight the role of poly3,4-ethylenedioxythiophene-polystyrenesulfunate (PEDOT:PSS) in tandem with TiO2 anodically grown by plasma electrolytic oxidation on pure Ti substrate. The addition of 1–10 wt.% citric acid as cross-linking agent enables PEDOT:PSS to work properly as a protective coating under aqueous conditions. We found that excessive amounts of citric acid led to the formation of micro- and nano-scale clusters of PEDOT:PSS on TiO2 surface, which are detrimental to the barrier effect against the corrosive medium. Thus, polarization and impedance test results suggested that the use of 1 wt.% of citric acid resulted in PEDOT:PSS@TiO2 layer with superior corrosion resistance. Furthermore, analysis of space charge capacitance reveals a decrease in the donor density, as calculated from Mott–Schottky plot of PEDOT:PSS@TiO2, pertaining to its passivation effect against ion and electron diffusion.

Keywords

• Plasma electrolytic oxidation
• PEDOT:PSS
• Cross-linking
• Composite
• Corrosion