The compression of PEM fuel cells has a significant impact on performance, particularly at high current densities where the ohmic contribution of mass transport and contact losses are major contributors. Compression, or more accurately the compressive stress on the fuel cell membrane electrode assembly (MEA), affects the mass transport of gases and water through the gas diffusion media (GDM). The transport of gases and water in turn affects the kinetics of the cells.

This talk will review our work toward better understanding how the compressive stress affects fuel cell performance. We observe that a break-in compression cycle decreases the contact or ohmic resistance between the GDM and metal bipolar plates when forming a high performance fuel cell stack, as the cycling appears to improve the interface between the porous GDM and roughness of the metal surface [1]. In a following effort to make laboratory-scale high performance MEAs, we observed that the compressive stress on the MEA was largely absorbed by the GDM, and the resulting porous structure of the compressed GDM had a large effect on overall performance at >0.2 A cm^-2 due to the influence on both ohmic losses and transport effects [2]. We therefore recommended attention to compression of the MEA/GDM as a major influence in the performance of high performance fuel cells [3]. While a compression near 14% is recommended for paper-type GDM in laboratory cells that use rigid gaskets as compression stops [2,3], we see that much greater compression is desirable for fuel cells in “open air” configurations, for which the air is very dry [4]. Three-dimensional imaging of paper- and felt-type GDM with computed tomography shows a clear correlation between how the porosity of the GDM vs compression affects fuel cell performance, and that higher compressive stress is advantageous for fuel cells with felt-type GDM [5].

References

1. C. Netwall, B. D. Gould, J. A. Rodgers, N. J. Nasello, K. Swider-Lyons, J. Power Sources, 227, 137 (2013).
2. M. B. Sassin, Y. Garsany, B.D.Gould, K. Swider-Lyons, J. Electrochem. Soc., 163, F808 (2016).
3. M. B. Sassin, Y. Garsany, B.D. Gould, K. Swider-Lyons, Anal. Chem., 89(1), 511 (2017).
4. R. W. Atkinson III ,M. W. Hazard, J. A. Rodgers, R. O. Stroman, B. D. Gould, ECS Trans., 75(14), 531 (2016).
5. R. W. Atkinson III, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, I. V Zenyuk, ACS Appl. Energy Mater., 1(1), 191 (2018).

Acknowledgements

We are grateful to the Office of Naval Research for their longstanding support of this research.