Bipolar membrane fuel cells (BMFCs) have been discussed in the past few years as a potential game-changer for the fuel cell community (1). In the most favorable alignment for fuel cell operation, BMFCs comprise an acidic anode (HOR) and an alkaline cathode (ORR), where protons and hydroxide ions are formed, respectively. The ions migrate through a proton or anion exchange membrane to the bipolar junction, where they combine to form water. Optimizing this interfacial reaction is critical to a high performance cell, but outside of recent modeling work (2, 3), few studies have paid specific attention to it.

In this study, a series of BMFC membrane electrode assemblies (MEAs) were fabricated where the proton exchange side comprised a Nafion 211 membrane and ionomer, and the alkaline membrane/ionomer were varied. All MEAs contained platinum on carbon electrode catalysts and were investigated via polarization curves and impedance. Initial MEAs made with several different AEM polymers exhibited an exorbitant cell resistance, attributed to the bipolar interface. To reduce cell resistance, bipolar membrane fabrication conditions were altered to study parameters that impact observed performance. Altering fabrication conditions resulted in nearly a 3x reduction in overall resistance, translating to large gains in BMFC performance. These fabrications methods will be summarized with results presented, which should help inform rational design and future work for BMFCs.

References

1. M. Ünlü, J. Zhou and P. A. Kohl, The Journal of Physical Chemistry C, 113, 11416 (2009).

2. K. N. Grew, J. P. McClure, D. Chu, P. A. Kohl and J. M. Ahlfield, J. Electrochem. Soc., 163, F1572 (2016).

3. Q. Li, J. Gong, S. Peng, S. Lu, P.-C. Sui, N. Djilali and Y. Xiang, J. Power Sources, 307, 358 (2016).

Figure 1. Example polarization curves for BMFC MEAs in H₂/O₂ at 60°C with and without membrane pretreatment.