Water in Polymer Electrolyte Fuel Cells (PEFCs): Friend or Foe? Linking Preferential Catalyst Growth with Liquid Water Distribution in PEFCs
Authors: Sharma Preetam , Boillat Pierre , Cheng Lei , Aaron Douglas S , Craig Nathan , Johnston Christina , Mench Matthew M 
Published: August 2024

With a recent emphasis on heavy-duty vehicle applications over light-duty, the performance targets for polymer electrolyte fuel cells (PEFCs) have become more demanding. For instance, achieving a net power output of 2.5 kW/g-PGM (1.07 A/cm2 current density) at 0.7 V is required after a 25,000-hour equivalent accelerated stress test (AST) [1]. In recent studies with traditional land/channel architecture, it has been demonstrated that Pt particle size growth is non-uniform and greater under flow field lands compared to channels [2]–[5]. It is hypothesized that preferential water accumulation under the lands during ASTs is responsible for such heterogeneity. However, a direct link between water accumulation/storage and particle size growth has not yet been established. In this study, we utilized high-resolution neutron radiography at NEUTRA, PSI, Switzerland to systematically map and quantify through-plane water content; synchrotron micro-XRD measured spatial Pt particle size distributions in fully functional fuel cells compatible with neutron imaging.

The membrane electrode assemblies (MEAs) were aged using the U.S. Department of Energy’s (DOE) square-wave AST (0.6 V to 0.95 V vs. reversible hydrogen electrode, RHE) in both air and nitrogen environments at the cathode [5]. Correlations between through-plane water distribution and Pt particle size distribution maps were established for both pristine and aged samples. Understanding the role of architecture is crucial for assessing degradation, particularly in conventional flow fields where channel-land bias influences thermal and mass transport, impacting liquid water distribution. This knowledge can inform the design and engineering of PEFC components to enhance durability and reduce overall costs for vehicle applications.

References:

[1] D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers, and A. Kusoglu, “New roads and challenges for fuel cells in heavy-duty transportation,” Nat Energy, vol. 6, pp. 462–474, 2021, doi: 10.1038/s41560-021-00775-z.

[2] L. Cheng, K. Khedekar, M. Rezaei Talarposhti, A. Perego, M. Metzger, S. Kuppan, S. Stewart, P. Atanassov, N. Tamura, N. Craig, I. V. Zenyuk, and C. M. Johnston, “Mapping of Heterogeneous Catalyst Degradation in Polymer Electrolyte Fuel Cells,” Adv Energy Mater, vol. 2000623, pp. 1–7, 2020, doi: 10.1002/aenm.202000623.

[3] K. Khedekar, M. R. Talarposhti, M. M. Besli, S. Kuppan, A. Perego, Y. Chen, M. Metzger, S. Stewart, P. Atanassov, N. Tamura, N. Craig, L. Cheng, C. M. Johnston, and I. V Zenyuk, “Probing Heterogeneous Degradation of Catalyst in PEM Fuel Cells under Realistic Automotive Conditions with Multi-Modal Techniques,” Adv Energy Mater, vol. 11, no. 35, p. 2101794, 2021, doi: 10.1002/aenm.202101794.

[4] P. Sharma, B. Bera, D. Aaron, M. M. Besli, S. Kuppan, L. Cheng, J. Braaten, N. Craig, S. Stewart, M. Metzger, C. Johnston, and M. M. Mench, “Spatially Resolved Heterogeneous Electrocatalyst Degradation in Polymer Electrolyte Fuel Cells Subjected to Accelerated Aging Conditions,” J Electrochem Soc, vol. 169, no. 11, p. 114506, Nov. 2022, doi: 10.1149/1945-7111/ac9ee5.

[5] P. Sharma, L. Cheng, D. Aaron, S. Mehrazi, J. Braaten, N. Craig, C. Johnston, and M. M. Mench, “Unveiling Local Aging Patterns Following Accelerated Stress Testing of High-Performance Polymer Electrolyte Fuel Cells,” Small, no. 2306433, 2023, doi: 10.1002/smll.202306433.