Corrosion behavior of two bipolar plate materials in simulated PEMFC environment by electrochemical noise technique

The corrosion behavior of 316L stainless steel (316L) and bulk amorphous Zr₇₅Ti₂₅ (AB) alloy was studied using electrochemical noise (EN) in simulated polymer electrolyte membrane fuel cell (PEMFC) conditions at 25 and 80 °C. At open circuit potential, under H₂ environment, AB exhibited a higher corrosion-resistance than 316L and the contrary was observed under O₂ environment. At imposed cathodic potential, under H₂ environment for PEMFC anodic simulation, the reduction mechanism of 316L at 80 °C gave the most important EN signals of all other conditions. At imposed anodic potential, under O₂ environment for cathodic simulation, the passive state was observed for 316L while severe localized corrosion for AB was obvious at 80 °C. It is concluded from the corrosion data of this work that in the anode environment of a PEMFC, the AB alloy could be a better candidate than 316L for bipolar plates. The contrary was observed in the simulated cathode environment.     

Effects of pH value and temperature on the corrosion behavior of a Ta2N nanoceramic coating in simulated polymer electrolyte membrane fuel cell environment

To improve the corrosion resistance and electrical conductivity of Ti-6Al-4V bipolar plates used in polymer electrolyte membrane fuel cells (PEMFCs), a novel electro-conductive Ta₂N nanoceramic coating was developed by reactive sputter-deposition using a double cathode glow discharge plasma technique. The microstructure of the coating consisted of fine equiaxed Ta₂N grains with an average grain size of ∼13 nm, which exhibited a strong (101) preferred orientation. To explore the influence of both pH values and temperatures on the corrosion resistance of the coating, the electrochemical behaviors and electronic properties of passive films grown on the Ta₂N coating were systematically investigated using different electrochemical techniques in simulated PEMFC operating environment. It was shown that either increasing the acidity or the temperatures of the solution, the corrosion potential (E_corr) decreased and the corrosion current density (i_corr) increased. At a given temperature or pH value, the Ta₂N coating had a higher E_corr and lower i_corr as compared with uncoated Ti-6Al-4V. The results of EIS measurements showed that with increasing temperature or acidity of the solution, the resistance of the passive film (R_p) formed on the Ta₂N coating decreased slightly, being of the order of magnitude of 10⁷ Ω cm², which was an order of magnitude higher than that of uncoated Ti-6Al-4V. The interfacial contact resistance (ICR) values were found to increase with increasing pH value or decreasing solution temperature, and the ICR values of the Ta₂N coating were markedly lower than that of uncoated Ti-6Al-4V, due to the thinner thickness of passive films. Furthermore, the Ta₂N-coated Ti-6Al-4V is more hydrophobic than bare Ti-6A1-4V, which was favorable for both the simplification of water management and improving corrosion resistance in PEMFC operating environment.