A model for a vertical planar air breathing PEM fuel cell

This paper presents a two-dimensional, steady state, single phase, non-isothermal and complete model for a vertical, fully planar, Air Breathing Proton Exchange Membrane Fuel Cell (AB-PEMFC) with hydrogen fuel supplied by forced convection at the anode. It is applied to a cell with an active area of 6 cm 2 operating at ambient atmospheric conditions of 23 degrees C and 20% relative humidity. The transport characteristics in terms of the velocity, and heat and mass transfer coefficients in the various components of the fuel cell are reported for several values of the operating current density. The effect of cathode height (1-5 cm) and operating atmospheric conditions (10-40 degrees C and 20-80% relative humidity), on the cell performance is also reported. Further, the applicability of the model to a non-planar AB-PEMFC is examined by comparison with available experimental data. The average mass transfer coefficients for oxygen and water vapor at the cathode GDL surface are found to be of the order of 10(-3) m s(-1). The operating current density is seen to substantially affect the variation of the local current density distribution and the cathode surface temperature along the height of the fuel cell as also the temperature variation across the MEA thickness. The maximum power density and the corresponding current density, herein defined as the optimum current density, are found to increase with decreasing height of the fuel cell, decreasing ambient temperature and increasing ambient relative humidity. However, the local cell temperature at high current densities is found to increase beyond the safe operating limits for short fuel cells. Comparison of the model predictions with available experimental data points to its applicability in the ohmic polarization zone of a non-planar cell. The cell performance at high current densities deteriorates due to mass transport limitation and electrolyte dehydration. (c) 2006 Published by Elsevier B.V.