Anion-exchange membrane fuel cells (AEMFCs) offer a potential advantage over their traditional proton-exchange membrane counterparts in that many non-precious metal catalysts are chemically compatible with the alkaline environment in an AEMFC [1]. Recently, high-power operation of AEMFCs has been demonstrated, including achieving 1 W/cm² using silver metal cathode catalysts [2], [3]. The performance of AEMFCs, however, can be highly sensitive to small changes in relative humidity, as water is a reactant in the alkaline oxygen reduction reaction. Additionally, performance degradation due to carbon dioxide contamination remains a major issue. The absorption of carbon dioxide and subsequent conversion to carbonate anions reduces membrane conductivity and worsens fuel cell performance.

In this work, we use our previously developed two-dimensional model [4] to illustrate and explore the effects of membrane and ionomer properties, relative humidity changes, and absorption of carbon dioxide on AEMFC performance. A 2+1D modeling approach is used, where an external stepping model is used to move along the gas channels. At each step, the 2D cross-section model [4] is used to simulate cell performance. Mass and energy balances are performed at each step to obtain the channel conditions, such as concentration, relative humidity, and temperature, for the subsequent step. The 2+1D model accounts for the performance changes due to concentration and relative humidity changes along the channel, especially at integral cell conditions. Finally, we show how performance limitations from carbon dioxide absorption, flooding, and dry-out could be alleviated through changes in operating parameters or ionomer properties.

Acknowledgements

The work was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231. We thank Bryan Pivovar and the members of the Fuel Cells group of the National Renewable Energy Laboratory for helpful discussion and model validation data.

[1] J. R. Varcoe et al., “Anion-exchange membranes in electrochemical energy systems,” Energy Environ. Sci., vol. 7, pp. 3135–3191, 2014.

[2] D. R. Dekel, “A mini-review on cell performance in anion exchange membrane fuel cells,” J. Power Sources, p. submitted, 2017, 2017.

[3] L. Wang and J. R. Varcoe, “The first anion-exchange membrane fuel cell to exceed 1 W cm-2 at 70 °C with a non-Pt cathode,” Chem. Commun., pp. 1–3, 2017.

[4] H.-S. Shiau, I. V. Zenyuk, and A. Z. Weber, “Elucidating Performance Limitations in Alkaline-Exchange- Membrane Fuel Cells,” J. Electrochem. Soc., vol. 164, no. 11, pp. E3583–E3591, 2017.