Characteristics of amorphous carbon films to resist high potential impact in PEMFCs bipolar plates for automotive application

The demands for lightweight, low cost and high power density of proton exchange membrane fuel cells (PEMFCs) have made stainless steel coated with amorphous carbon (a-C) film an ideal alternative material to replace graphite for bipolar plates in automotive application. However, the existing a-C film cannot resist high potentials generated during vehicle operating conditions such as start-stop process, high power loading condition, which result in carbon corrosion and undoubtedly decrease the lifetime of fuel cells. Therefore in this study, we designed three types of a-C films comprising Cr, Ti and Nb seed layers based on the materials E-pH diagrams. The a-C films were deposited through closed unbalanced magnetron sputtering and characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman methods. The durability of a-C films were evaluated through potentiostatic polarization tests by applying different high potentials. When applied potential exceeds 1.2 VSHE, the a-C film with Cr seed layer will be delaminated from the substrate due to the dissolution of Cr element. While the a-C films with Ti or Nb layer exhibit an excellent corrosion resistance even the applied potential as high as 1.6 VSHE. After potentiostatic polarization tests, the interfacial contact resistance (ICR) values increased mechanism were determined through Raman and XPS detection comprehensively. This present study will shed new light on solving the high potential impact and improving the lifetime of fuel cells vehicles.