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Controlling the ionic polymer/gas interface property of a PEM fuel cell catalyst layer during membrane electrode assembly fabrication

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Abstract

During high current density operation, water production in the polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst layer can negatively affect performance by lowering mass transport of oxygen into the cathode. In this paper, a novel heat treatment process for controlling the ionic polymer/gas interface property of the fuel cell catalyst layer is investigated and then incorporated into the membrane electrode assembly (MEA) fabrication process. XPS characterization of the catalyst layer's ionomer-gas interface at its outer surface and its sublayers’ surfaces obtained by scraping off successive layers of the catalyst layers confirms that a hydrophobic ionomer interface can be achieved across the catalyst layer using a specific heat treatment condition. Based on the results of the catalyst layer study, the MEA fabrication process is modified to identify heat treatment configuration and conditions that will create an optimal hydrophobic ionomer-gas interface inside the cathode catalyst layer. Finally, fuel cell tests conducted on the conventional and new MEAs under different operating temperatures show the performance of the fuel cells with the treated MEAs was > 130% higher than that with the conventional MEA at 25 °C and 70 °C with humidified air and > 45% higher at 70 °C with dry air. The durability of the hydrophobic treatment on the cathode catalyst layer ionomer is also confirmed by the accelerated stress test.

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PEMFC Catalyst Layer with Hydrophobic Ionomer/Gas Interface

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Acknowledgements

Regis Dowd Jr. wishes to acknowledge the financial support from the University of Kansas (KU) Madison and Lila Self Fellowship. The authors would like to thank Dr. Prem Thapa at the University of Kansas and Dr. Vijay Ramani, Dr. Huafang Li, and Yue Li at Washington University in St. Louis for their support and expertise in using the XPS. The authors would also like to thank Applied Porous Technologies, Inc. for providing the porous stainless-steel disk used for MEA fabrication. This work was also supported by the National Science Foundation under Grant Numbers EFRI-1038234 and CBET-1518755/1803058.

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  1. Department of Chemical and Petroleum Engineering, The University of Kansas, 1530 W. 15th, Learned Hall Room 4132, Lawrence, KS, 66045, USA

    Regis P. Dowd Jr., Yuanchao Li & Trung Van Nguyen

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  1. Regis P. Dowd Jr.
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  2. Yuanchao Li
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Contributions

The research was done by RPD under the direction of TVN. The manuscript was written by both RPD and TVN. YL conducted additional experiments to obtain the results in Figs. 4 and 8 and provided additional analysis of these results.

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Correspondence to Trung Van Nguyen.

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The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Contribution to the field statement

During high current density operation, liquid water production in the polymer electrolyte membrane fuel cell cathode catalyst layer can negatively affect performance by lowering mass transport of oxygen into the cathode. In this paper, a novel heat treatment process for making the ionic polymer/gas interface of the fuel cell catalyst layer hydrophobic is incorporated into the membrane electrode assembly (MEA) fabrication process. The hydrophobic ionomer layer interface helps to keep the ionomer free of liquid water and therefore more accessible to oxygen gas. It also helps to expel water more rapidly from the gas pores in the catalyst layer. Fuel cell test results of MEAs fabricated by this process show improved performance compared to conventional MEAs, especially under high water saturation operating conditions. The fuel cell performance of the treated MEA was > 130% better than the conventional MEA at both 25 °C and 70 °C when supplying humidified air and > 45% better at 70 °C with dry air.

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Dowd, R.P., Li, Y. & Van Nguyen, T. Controlling the ionic polymer/gas interface property of a PEM fuel cell catalyst layer during membrane electrode assembly fabrication. J Appl Electrochem 50, 993–1006 (2020). https://doi.org/10.1007/s10800-020-01453-w

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