Mitigating the Corrosion of Anodized 304 and 316 Stainless Steel with GOx/PEDOT Coating for Bioelectrochemical Saline Water Applications
Authors: Abd El-Hamid Shimaa E , Aly Islam A , Heiba Asmaa R. , Omran Mostafa M. , El Sawy Ehab N 
Published: August 2024

Steels are the most used alloys worldwide as they have superior mechanical properties, such as ductility and elasticity. Stainless steel (SS) is used far and wide from infrastructure, households, vehicles, surgical equipment, and medical implants, to electrochemical applications such as supercapacitors, fuel cells, lithium-ion batteries, aqueous rechargeable batteries, and bioelectrochemical systems (BES)1 such as microbial fuel cells (MFCs)2 and microbial electrolysis cells (MECs)3. Even though oxidized stainless steel is a very effective electrode material for BES, it has a high risk of corrosion due to the removal of the protective Cr-based passive oxide layer4.

Hereby, this research aims to investigate the corrosion behavior of anodized stainless steel (SS) 304 and 316 mesh in saline water for potential use in BES with high salinity and try to mitigate that corrosion behavior using biocompatible materials. The tested electrodes include SS304 and SS316 mesh before and after anodization (anodized SS, AN-SS), in comparison to AN-SS coated with double layers of graphene oxide (GOx) and poly(3,4-ethylenedioxythiophene) (PEDOT). SS 304 and 316 were anodized using selective leaching protocol to enhance the removal of the bioincompatible and insulating Cr-based layer. The removal of that layer makes SS more susceptible to dissolution and hence further protection is needed. Both GOx and PEDOT were selected to enhance the surface conductivity, biocompatibility, and corrosion resistance. GOx was synthesized using the electro-exfoliation of a graphite sheet at a constant voltage of 10.0 V in terephthalic acid + NaOH solution, followed by centrifuging at 3000 rpm to remove the large particles.5 After several cycles of washing, the freeze-dried GOx was mixed with Nafion for ink preparation, which was used to coat the An-SS using the spray coating method. The coated electrode was further covered with a PEDOT layer, using the chronpotentiometry electropolymerization method (2 mA/cm2, for 10, 30, or 60 min). Several characterization techniques such as SEM, EDX, XPS, FT-IT, Raman spectroscopy, XRD, and TEM, were used to characterize the physical and chemical structure of the coating materials and the the fabricated electrodes. The corrosion behavior was evaluated using potentiodynamic and potentiostatic methods. Based on the anodic polarization results, the corrosion, passivation, and breakdown (due to dissolution) regions were identified. In this presentation, the corrosion behavior (Ecorr, Icorr, breakdown potential, etc) of the studied electrodes will be correlated with their chemical and physical structures.

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