MEA with Thin Pore-Filling Anion Exchange Membrane and Water Transport Analysis in SAFC

The solid-state alkaline fuel cells (SAFCs) with anion exchange membranes (AEMs) have attracted considerable attention because of applying non-noble metal catalysts in alkaline condition. However, unlike the proton-exchange membrane fuel cells (PEFCs), SAFC is under development and shows low cell performance. One of the reason for the low performance in SAFC is due to flooding occurred by generated water at the anode¹⁾. If a thin AEM is used, the generated water at the anode will be able to move easily to the cathode, and as a result, the cell performance will be improved.

In our study, we developed the membrane electrode assembly (MEA) with the thin AEM and analyzed the water transport inside the MEA. Catalyst layers (mixture of the commercial Pt/C catalyst, poly(vinylbenzyl chloride), and Nafion) were transferred via decal method onto the both sides of pore filling membranes synthesized by vinyl benzyl trimethylammonium chloride with different thickness having 25 μm and 5 μm. Then the I-V test was performed at 60 ºC with the humidified H₂/O₂ supplied. To evaluate the permeance of each AEM, outlet dew point of each electrode was also measured using the water transport analysis system²⁾. As shown in Fig. 1, the I-V performance was greatly improved by the usage of thinner AEM. The permeance of the MEA with 5 μm thickness membrane increased by 2.4 times compared with that with 25 μm thickness. Under the water permeation analysis condition, anode RHs were also calculated from the water mass balance equation of both MEA and the whole cell to estimate the flooding region of each MEA. When the anode RH reached over 100 %, the MEA with 5 μm thickness membrane showed higher current density compared with the MEA using 25 μm thickness membrane. The flooding at the anode can be suppressed by using thinner AEM, leading to increment of I-V performance.

Reference

1) H. Zhang, H. Ohashi, T. Tamaki, T. Yamaguchi, J Phys Chem C, 116, 7650-7657(2012).

2) Y. Oshiba, H. Irizawa, H. Ohashi, T. Yamaguchi, In-Situ Measurement and Analysis of Water Movement in PEFCs, 226^th ECS meeting, Cancun (2014).