Cathode Catalyst Layer Performance Research Articles

The effect of Nafion film on the cathode catalyst layer performance in a low–Pt PEM fuel cell

A single–pore model for performance of the cathode catalyst layer (CCL) in a PEM fuel cell is developed. The model takes into account oxygen transport through the CCL depth and through the thin Nafion film, separating the pore from Pt/C species. Analytical solution to model equations reveals the limiting current density jNlim due to oxygen transport through the Nafion film. Further, jNlim linearly depends on the CCL thickness, i.e., the thinner the CCL, the lower jNlim. This result may explain unexpected lowering of low–Pt loaded catalyst layers performance, which has been widely discussed in literature.

Establishing Targets for the Cathode Catalyst Layer Kinetic & Transport Parameters in PEMFC Designs

Introduction Commercializing polymer electrolyte membrane fuel cells (PEMFC) is ultimately a matter of achieving the necessary cost for broad market penetration. Cost is a function of materials, manufacturability, performance, and durability. Performance and durability targets have been set by the DOE [1] to provide guidance and focus to the PEMFC industry for specific applications such as the automotive sector. To cascade these challenging targets down to material and transport requirements we employ a fully integrated performance model to conduct parameter optimization studies in tandem with experimental validation. Design curves are utilized as inputs to the model to provide the current state-of-the-art capability regarding catalyst activity and ionomer proton conductivity. High performing commercial membrane and GDL components were selected with a standard catalyst (Figure 1) to provide a baseline for this evaluation. The gap between modelled MEA performance and DOE targets will be highlighted and a recommended path forward will be provided. Results & Discussion Aside from catalyst activity and available surface area, the cathode catalyst layer performance is dictated by the mass transport of protons (proton conductivity), oxygen (gas diffusivity), and water (gas & liquid permeability) [2-4]. Several material sets have been evaluated experimentally in-situ to provide a range in catalyst activity, proton conductivity, and effective layer diffusivity as shown in figures 1 and 2 (diffusivity not shown). During operation the distribution of current through the porous three dimensional catalyst layer structure [6] is dictated by the catalyst activity and layer transport properties. We will describe in this work the relationship between proton conductivity and voltage performance. Based on these results we can set relevant conductivity targets, which can be used for both ionomer development and material down selection. These parameters will be utilized in the Ballard/DOE funded FC-Apollo performance model to provide the current status toward achieving the DOE’s 2020 automotive targets listed in Table 1. Further, technology gaps will be identified in conjunction with a strategy toward meeting these objectives. Acknowledgement The authors would like to acknowledge Joey Jickain for his testing support and National Resources Canada (NRCan), National Research Council of Canada (NRC-IRAP), and the US Department of Energy (DOE) for funding various aspects of this work. Reference 1. http://energy.gov/eere/fuelcells/doe-technical-targets-polymer-electrolyte-membrane-fuel-cell-components2. Egushi, M., Baba, K., Onuma, T., Yoshida, K., Iwasawa, K., Kobayashi, Y., Uno, K., Komatsu, K., Kobori, M., Nishitani-Gamo, M., Ando, T., Polymers, 4, p. 1645 (2012)3. Xie, J., Xu, F., Wood, D.L., More, K.L., Zawodzinski, T.A., Smith, W.H., Electrochimica Acta 55 p. 7404 (2010)4. Gode, P., Jaouen, F., Lindbergh, G., Lundblad, A., Sundholm, G., Electrochimica Acta 48 p. 4175 (2003)5. Young, AP., Gyenge, E., Stumper, J., J. Electrochem. Soc., 156, B913 (2009) 6. Young, AP., Knights, S., Gyenge, E., Stumper, J., J. Electrochem. Soc., 157, B425 (2010) Figure 1

A study of the agglomerate catalyst layer for the cathode side of a proton exchange membrane fuel cell: Modeling and optimization

A comprehensive mathematical model for the cathode catalyst layer (CL) of a proton exchange membrane fuel cell (PEMFC) is developed to investigate its performance, which is determined by activation overpotential. Numerous cathode CL parameters such as the saturation and eight structural parameters, namely, ionomer film thickness covering each agglomerate, agglomerate radius, platinum loading, carbon loading, ionomer volume fraction, gas diffusion layer penetration content and its porosity, and CL thickness are taken into account. The main effects of each parameter and their interactions are investigated using the analysis of means (ANOM) and interaction plots, respectively. Analysis of variance (ANOVA) is used to identify the influence of the CL structural parameters on the activation overpotential. Finally, an evolutionary optimization algorithm is employed to maximize the cathode CL's performance.