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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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Modification of Nafion's nanostructure for the water management of PEM fuel cells
Abstract A PEM fuel cell with the Nafion ionomer phase of the cathode catalyst layer (CL) that was exposed to hot dry gas during the hot‐pressing process showed improved performance over the whole current density range and ~ 220% peak power increase with humidified air at 80°C. This enhanced performance is attributed to the modified structure of the perfluorosulfonic acid (PFSA) ionomer layer in the CL during the MEA's hot‐pressing process. The dry gas exposure above the glass transition temperature (Tg) results in the aggregation of the ionic groups to retain the residue water molecules. This process separates the ionomer into ionic‐group‐rich domains and ionic‐group‐sparse domains. The ionic‐group‐sparse domains create hydrophobic interface and reactant transport channels with lower water content and thus higher oxygen solubility in the ionomer. Accordingly, the water‐unsaturated ionomer and its surface hydrophobicity enhance the kinetic‐controlled and concentration‐polarized regions of the fuel cell polarization curve, respectively. The surface hydrophobicity of the ionomer layer is analyzed by the contact angle measurement and XPS. The durability of the hydrophobic effect belowTgis demonstrated by boiling the treated material. Re‐treating the hydrophobic sample with humidified gas exposure aboveTgeventually exhibits hydrophilic features, further proving the manipulability of the ionic group distribution.
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- Award ID(s):
- 1803058
- PAR ID:
- 10406994
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Polymer Science
- Volume:
- 61
- Issue:
- 8
- ISSN:
- 2642-4150
- Page Range / eLocation ID:
- p. 709-722
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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