PEM fuel cell reaction kinetics in the temperature range of 23-120°C

The performance of a Nation 112 based proton exchange membrane (PEM) fuel cell was tested at a temperature range from 23 degrees C to 120 degrees C. The fuel cell polarization curves were divided into two different ranges based on current density, namely, < 0.4 A/cm(2) and > 0.4 A/cm(2), respectively. These two ranges were treated separately with respect to electrode kinetics and mass transfer. In the high current density range, a linear increase in membrane electrode assembly (MEA) power density with increasing temperature was observed, indicating the advantages of high temperature operation. Simulation based on electrode reaction kinetic theory, experimental polarization curves, and measured cathodic apparent exchange current densities all gave temperature dependent apparent exchange current densities. Both the calculated partial pressures of O-2 and H-2 gas in the feed streams and the measured electrochemical Pt surface areas (EPSAs) decrease with increasing temperature. They were also used to obtain the intrinsic exchange current densities. A monotonic increase of the intrinsic exchange current densities with increasing temperature in the range of 23-120 degrees C was observed, suggesting that increasing the temperature does promote intrinsic kinetics of fuel cell reactions. There are two sets of cathode apparent exchange current densities obtained, one set is for the low current density range, and the other is for the high current density range. The different values of cathode current densities in the two current density ranges can be attributed to the different states of the cathode Pt catalyst surface. In the low current density range, the cathode catalyst surface is a Pt/PtO, and in the high current density range, the catalyst surface becomes pure Pt. (c) 2006 Elsevier Ltd. All rights reserved.