Assessment of Carbon-Titanium Multilayer Coatings on Aluminum as Bipolar Plates in PEM Fuel Cells

Aluminum is an appropriate candidate for bipolar plates in proton exchange membrane (PEM) fuel cells because it reduces the final cost and weight of the fuel cell stack in comparison to stainless steel, titanium and graphite. However, a conductive coating layer is essential to protect it against corrosion. In this study, the electrochemical behavior of aluminum coated with titanium and amorphous carbon layers by physical vapor deposition is evaluated. The main goal is to investigate the corrosion protection performance and the possible failure reasons of the coating in sulfuric acid solutions (with different pH values) in the presence of 3 ppm sodium fluoride and elevated temperature (80 °C) to mimic the working conditions of PEM fuel cells. To reach our aim, electrochemical tests are combined with surface analysis techniques. It is revealed that at low pH values (pH = 2 and 3), the coating fails due to the acidity of the electrolyte solutions. However, in the electrolyte with pH = 4, present fluoride ions interfere and consequently lead to localized failures. It is noticed that the presence of defects in the coating is a key parameter in the application of coated aluminum as bipolar plates in PEM fuel cells.