Ex-situ evaluation of PTFE coated metals in a proton exchange membrane fuel cell environment

• Published in: Surface & coatings technology 2017-08, Vol.323, p.10-17
• Main Authors: Baroutaji, A., Carton, J.G., Oladoye, A.M., Stokes, J., Twomey, B., Olabi, A.G.
• Format: Article
• Language: English
• Subjects: Alloy steels; CoBlast; Conductivity; Contact angle; Contact resistance; Corrosion; Corrosion resistance; Corrosion resistant alloys; Corrosion resistant steels; Electric contacts; Electrical resistivity; Flow plates; Fuel cells; Hafnium; Hydrophobicity; Interfacial contact resistance; PEM fuel cell; Plates; Polytetrafluoroethylene; Protective coatings; Proton exchange membrane fuel cells; PTFE coatings; Stainless steel; Titanium; X-ray diffraction
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2016.11.105

Metallic-based bipolar plates exhibit several advantages over graphite-based plates, including higher strength, lower manufacturing cost and better electrical conductivity. However, poor corrosion resistance and high interfacial contact resistance (ICR) are major challenges for metallic bipolar plates used in proton exchange membrane (PEM) fuel cells. Corrosion of metallic parts in PEM fuel cells not only increases the interfacial contact resistance but it can also decrease the proton conductivity of the Membrane Electrode Assembly (MEA), due to catalyst poisoning phenomena caused by corrosive products. In this paper, a composite coating of polytetrafluoroethylene (PTFE) was deposited on stainless steel alloys (SS304, SS316L) and Titanium (G-T2) via a CoBlast™ process. Corrosion resistance of the coated and uncoated metals in a simulated PEM fuel cell environment of 0.5M H2SO4+2ppm HF at 70°C was evaluated using potentiodynamic polarisation. ICR between the selected metals and carbon paper was measured and used as an indicator of surface conductivity. Scanning Electron Microscopy (SEM), 3D microscopy, Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and contact angle measurements were used to characterise the samples. The results showed that the PTFE coating improved the hydrophobicity and corrosion resistance but increased the ICR of the coated metals due to the unconductive nature of such coating. Thus, it was concluded that it is not fully feasible to use the PTFE alone for coating metals for fuel cell applications and a hybrid coating consisting of PTFE and a conductive material is needed to improve surface conductivity. •PTFE coated metals were evaluated for PEM fuel cell bipolar plate applications.•CoBlastTM process was used to deposit a PTFE coating on the metal substrates.•Samples were characterised using SEM/EDX, XRD, and potentiodynamic polarisation techniques.•The PTFE coating was found to increase the corrosion resistance but decrease the surface conductivity