Study of through Plane Cation Contamination in Polymer Electrolyte Fuel Cell

The effect of through plane cation contamination on PEFC was investigated using a multilayered membrane cell. The MEA, similar to Watanabe et al. (1, 2), was prepared using five layers of Nafion® 211 (~1 mil=25.4 μm thickness) membrane, and four Pt wires (electrodes) were placed between the membranes (Figure 1). Pt electrodes were used to monitor the through-plane potential that results from the permeation of hydrogen and oxygen from anode and cathode, respectively. 1.14 mM CaSO₄ solution was injected into the air stream through a nebulizer at a rate of 65 μL/min, corresponding to a 5 ppm of CaSO₄based on dry air. Both the anode and the cathode flow fields were made of aluminum alloy, T6061 and were gold-plated to prevent corrosion.

As shown in Figure 2, the electrode closest to the cathode showed the same potential to the cell voltage and all the other electrodes showed zero potential. At the electrode closest to cathode, the potential was dominated by oxygen permeated from cathode, and in the other electrodes, oxygen permeated from cathode was negligibly smaller than hydrogen permeation, and the electrode potential was dominated by hydrogen oxidation reaction. After 32 hours with pure air, there was enough oxygen permeation from the cathode to other layers of membrane to symbolize the membrane degradation.

Posttest analyses showed that in spite of the gold plating, the aluminum flow fields were corroded. Aluminum corrosion byproducts degraded the cell performance from the beginning of the test. When CaSO₄ was injected with air, the cell performance degraded rapidly (Figure 2). Aluminum was deposited as Al₂O₃ or Al(OH)₃on the flow field and GDE surfaces causing mass transport losses. No calcium/sulfur was detected in the deposit from EDX analysis. It might happen that the presence of calcium/sulfur in the deposit was below the detection limit of EDX.

HFR was increased due to contamination. In the membrane layer close to the cathode, the HFR increase was more than 50% (Figure 3).

Acknowledgements

The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

References 

1. S. Takaichi, H. Uchida and M. Watanabe, Electrochemistry communications, 9, 8 (2007).

2. S. Takaichi, H. Uchida and M. Watanabe, J. Electrochem. Soc., 154, 12 (2007).