Abstract:
In the present study, the corrosion behavior of sputter-deposited amorphous Al-40Cr-xMo alloy coatings in 0.5 M H2SO4 + 2 ppm NaF solution at 70 degrees C (+/- 2 degrees C) was investigated for a possible application as bipolar plates (BPPs) for proton exchange membrane fuel cells (PEMFCs). Particular attention was given to understand the effect of Mo concentration on the passive films and, thereby, on the corrosion behavior of the sputter-deposited alloy coatings. X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques were carried out to characterize the Al-40Cr-xMo coated specimens. XRD plots of the Al-40Cr-xMo coated specimens indicated the deposits to be amorphous in nature. SEM images showed the coatings were dense and uniform without the presence of any coating defects. XPS analysis indicated a depletion of Mo at concentrations above 12 at. pct. Potentiodynamic polarization test results indicated that the addition of Mo at approximately 12 at. pct is effective in enhancing the corrosion resistance by decreasing the passive current density. However, further addition of Mo raises the anodic current density, thereby lowering the protective ability of the passive film.