Anion-exchange membrane fuel cells (AEMFCs) offer a potential advantage over their traditional proton-exchange membrane counterparts in that AEMFCs can operate with non-precious metal catalysts [1]. Recently, high-power operation of AEMFCs has been demonstrated in laboratory-scale cells [2]. The performance of AEMFCs, however, can be highly sensitive to small changes in relative humidity due to the critical role of water in both the alkaline oxygen reduction reaction and in hydrating the membrane. Additionally, carbon-dioxide absorption and conversion to carbonate anions reduces membrane conductivity and worsens fuel-cell performance.

In this work, we use our previously developed two-dimensional model [3] to illustrate and explore the effects of membrane and ionomer properties, relative-humidity changes, and absorption of carbon dioxide on cell performance. We model local current density changes in large-area cells by stepping the two-dimensional model along the flow channel, updating it at each step to account for changes in gas concentration and relative humidity. 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 by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, 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.

References

[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, “Review of cell performance in anion exchange membrane fuel cells,” J. Power Sources, vol. 375, pp. 158–169, Jan. 2018.

[3] 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.