1. Model of PEM Fuel Cell Cathode Sarah Hipple EGEE 520 May 3, 2007

2. Introduction  PEM Fuel Cell Structure Platinum Electrodes  Very effective at splitting hydrogen at the anode  Less effective at splitting oxygen at the cathode  This Analysis: Focuses on transport of species through the Cathode Species Distribution Velocity of molecules

3. Governing Equations  Darcy's Law Conservation of mass & momentum balance Equation:  Maxwell-Stephan Equation Mass Balance Equation: whereand

4. Boundary Conditions (1) (2) (3)

5. Solution Parameters Basic Operating Conditions: T=80°C Atmospheric Pressure

6. Solution: Velocity Velocity:

7. Solution: Oxygen and Water Distribution From the left: Graph of oxygen mass fraction at 5 x values; Image of Oxygen mass fraction distribution; Image of water mass fraction distribution

8. Validation Comparison to work of Yi and Nguyen & He, Yi, and Nguyen On the left: Pressure On the right: Velocity Field

9. Parametric Study  Oxygen Concentration at the Interface with the Polymer Electrolyte Membrane Air as the cathodic feed (left image) Pure oxygen as the cathodic feed (right image)  Importance Drying out of the membrane (too much oxygen/air) Reduction of power output (too little oxygen/air) Carbon monoxide poisoning prevention

10. Conclusions  This model agrees with other authors’ models  This model can help determine species’ distributions and flow paths through the cathode in: The existing model A model with modified pressure, temperature, porosity, dimensions, or cathodic feed

11. Image Sources  Aguirre, Lauren. (2005, July). Nova: scienceNOW: How Fuel Cells Work: PBS. URL www.pbs.org/wgbh/nova/sciencenow/3210/01-fcw.html (visited 2007, January 30)  Yi, Jung Seok, & Nguyen, Trung Van. (1998, April). An along-the- channel model for proton exchange membrane fuel cells. Journal of The Electrochemical Society, 145 (4), 1149-1159.  He, Wensheng, Yi, Jung Seok, & Nguyen, Trung Van. (2000, October). Two-phase flow model of the cathode of PEM fuel cells using interdigitated flow fields. American Institute of Chemical Engineers. AIChE Journal, 46 (10), 2053-2064.