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

Abstract

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.

Corrosion resistance of NbN and NbxAlyN coatings on stainless steel

“…An equal 3-electrode cell apparatus and stabilization period was employed in the potentiodynamic polarization tests. Starting from −30 mV below the OCP, the potential was swept at a scanning rate of 1 mV s −1 [16][17][18][19]. Potentiodynamic tests were performed in triplicates.…”

Bipolar Plate Design Assessment: Proton Exchange Membrane Fuel Cell and Water Electrolyzer

“…However, the problem lies in the durability of Al in the corrosive environment of PEMFC. Havigh et al utilized the corrosion resistance of Ti and good conductivity of amorphous carbon in combination as protective layers over AA-1100, whereas Zhang et al also used multilayer coating (NiP/TiNO) on AA-6061 instead [33,34].…”

“…Copper (Cu) is another material that is worth highlighting for usage in PEMFC BPP for its excellent conductivities. Multiple studies have looked into the corrosion protection methods on Cu coated with octadecylamine-functionalized graphene/TiO 2 or graphite and found that they increased the corrosion resistance by orders of magnitude while also lowering the ICR [33]. Among all the different metallic BPP, Xu et al highlighted that Ti has the lowest average corrosion resistance [8], followed by Al and stainless steel [35], but the release of Al 3+ and Fe 2+ ions from the surface oxidation can contaminate the catalyst layer and cause performance loss [36,37].…”

Bias Voltage Dependency of Structural and Bipolar Plate-Related Properties of Cathodic Arc-Deposited Carbon-Based Coatings

“…In 2019, Tang et al published a work about the effect of duty cycle and bias voltage on graphite-like carbon using unbalanced magnetron sputtering with the conclusion that both deposition parameters significantly affect its properties. A different approach is the application of a multilayer coating composed of several layers, which is beneficial for the electrochemical properties. , However, the deposited coatings are comparatively thick, several hundred nanometers in size, and a rather complex process is employed. Overall, in most cases of the studies, magnetron sputtering is used as a deposition method, which has the drawbacks of a relatively low deposition rate, energy efficiency, and low ionization. , …”

“…A different approach is the application of a multilayer coating composed of several layers, which is beneficial for the electrochemical properties. 31,32 However, the deposited coatings are comparatively thick, several hundred nanometers in size, and a rather complex process is employed. Overall, in most cases of the studies, magnetron sputtering is used as a deposition method, which has the drawbacks of a relatively low deposition rate, energy efficiency, and low ionization.…”