A Study of Cationic Contamination and Mitigation on Gdl/MPL Wettability and Metallic Plate Corrosion for PEFCs

     Cationic impurities on performance loss are investigated by incorporation of foreign cation into the MEA in a form of salt solution. The hydrophobic property of the gas diffusion layer (GDL) acts as a barrier for transport of aqueous contaminant solution to reach the catalyst-coated membrane (CCM). In our previous work, the role of the GDL in cationic contamination and mitigation has been studied by an ex-situ soak method and an in-situ injection. Here, we present the effect of cationic solution to the water management in the cell and the metallic plate corrosion.

     Wetting property changes of the contaminated GDL and micro-porous layer (MPL) were tested using a force tensiometer, which is measured in the sample mass changes by contacting and penetrating the liquid. The three-phase boundary contact of solid-liquid-gas onto the GDL is moving during the fuel cell operation, therefore dynamic contact angles were measured in advancing and receding angles by Wilhelmy balance method. The measuring sample was prepared by a double-sided adhesive tape to get the GDL or the MPL on both sides. Figure 1 shows water submersion cycles of the wetted surface force acting on Freudenberg C4 MPL-coated GDL for the as-received and after soaking in DI water and CaSO₄solution at 80 °C for 100hr. The contact angle can be calculated with the solid perimeter and the liquid surface tension because the measured force is related to the liquid-solid surface tension. The hydrophilic plain-paper GDL of Freudenberg C4 was resulted in larger contact angle hysteresis then the hydrophobic MPL. As shown in Table 1, the contaminated GDL shows the lowest contact angle in both immerging and emerging to the liquid, whereas there was no difference in the wetting property of MPL for all three cases due to its hydrophobicity. The GDL wettability after soaking in the DI water was also reduced by aging effects in the hot water for 100hr. Figure 2 shows wetting processes for the dynamic contact angle while measuring the force on the sample due to wetting.

     Cationic impurities are also originated from the corrosion of bipolar plates, current collecting plates, end plates and even tube fittings and piping systems. In addition, the corrosion rate accelerates when cell/system is tested with contaminated salt solution and acidic cleaning solution. Therefore, anodic corrosion measurements namely, polarization measurement (R_P), corrosion current (I_corr) and corrosion rate (I_CR) are performed for stainless tube fittings, aluminum endplates and gold coated copper current collecting plates in various concentrations of CaSO₄solution and cleaning solution of 10mM sulfuric acid.

Acknowledgements

Financial support from the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI) is greatly acknowledged.

References

[1] M. Uddin, J. Park, X. Wang, J. Qi, U. Pasaogullari, L. Bonville and T. Molter, ECS Transactions, 64 (3) 537-544 (2014)