Cathode catalyst utilization for the ORR in a PEMFC - Analytical model and experimental validation

The following model/experiment comparisons aid in predicting the maximum performance of a H-2/oxygen proton exchange membrane fuel cell (PEMFC) for a cathode catalyst with known oxygen reduction reaction (ORR) kinetics in the absence of gas transport resistances. Specific focus was on modeling the voltage loss within the cathode catalyst layer, which results from a balance between slow ORR kinetics and resistance to proton transport. A unique plot of proton resistance correction vs the ratio of ohmic (expressed by the proton conduction sheet resistance, R-sheet) to charge transfer resistance (expressed by the ratio of the Tafel slope of the ORR over the current density, b/i) in a PEMFC cathode (iR(sheet)/b) was developed, based on an analytical solution to effective proton resistance in the porous cathode electrode of a proton exchange membrane fuel cell. Additionally, a plot of catalyst utilization (u) vs iR(sheet)/b was developed to serve as a guideline of experimental design parameters such that catalyst utilization is kept above 90%, which is a prerequisite for measuring the ORR kinetics. The model is applicable as long as the ORR follow simple Tafel kinetics. (c) 2007 The Electrochemical Society. All rights reserved.