Influence of H+ and F− on corrosion behavior of a-C coatings in bipolar plates for PEMFCs

This study employed a filtered cathodic vacuum arc (FCVA) method to fabricate three types of amorphous carbon (a-C) structural coatings. Using Tafel analysis and 2-hour constant-potential tests under simulated fuel cell operating conditions, the effects of H + and F − concentrations on coating structure and corrosion resistance were investigated. Characterization techniques, including SEM surface morphology, energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and infrared spectroscopy, revealed that under high H + and F − concentrations, the C C sp 3 bonds in the coating prepared under a low bias voltage were transformed into sp 2 C bonds and C H bonds. In contrast, under high bias conditions, the sp 2 C bonds in coatings with higher sp 2 contents were severely contaminated, resulting in increased contact resistance. Notably, at high F − concentrations, the degree of phase transformation was more pronounced. After corrosion, the coatings underwent transformations not only from C C (sp 2 ) to C O bonds but also to C O and C C configurations.