Superior conducting polypyrrole anti-corrosion coating containing functionalized carbon powders for 304 stainless steel bipolar plates in proton exchange membrane fuel cells

The improvement in the long-term corrosion resistance of conducting polymer coatings was essential for protecting metal bipolar plate in proton exchange membrane fuel cell (PEMFC). In this study, carbon powders were functionalized with polydopamine (PDA) to create a more negative charge surface and their morphologies were examined by TEM test. Then, polypyrrole (PPy) coating was successfully electropolymerized on 304 stainless steel (304SS) in the presence of carbon powders (C and C-PDA powders). Therefore, the conducting property of PPy coating could be restored by incorporating carbon powders when the coating suffered aggressive attack. The structure, morphology and thermal-stability properties of the synthesized PPy, PPy/C and PPy/C-PDA coatings were investigated using SEM, AFM, FTIR and TG analysis. The anti-corrosion performances were also investigated in a simulated PEMFC working environment (0.1 M H₂SO₄ solution). Electrochemical tests and immersion tests showed that PPy/C-PDA coating exhibited superior long-term corrosion resistance during 720 h of immersion and the pitting phenomenon of 304SS was evidently avoided. The PPy/C-PDA coating served as a superior physical barrier and provided excellent anodic protection effect and adhesion strength, with a low interfacial contact resistance.