MODELISTIC INTERPRETATION OF THE IMPEDANCE RESPONSE OF A POLYMER ELECTROLYTE FUEL-CELL

In this work, several aspects related to the limiting polarization beh avior of polymer electrolyte fuel cells were studied using ac impedanc e spectroscopy. The results were analyzed taking into account the diff erent types of potential losses caused by the interfacial reaction kin etics, the conductance of the electrolyte in the catalyst layer, the o xygen diffusion in the gas phase, in the thin film and in the distribu ted agglomerate regions of the gas diffusion electrodes and the balanc e of water in the membrane. The main conclusion is that the water tran sport in the membrane plays an important role in establishing the limi ting polarization behavior of polymer electrolyte fuel cells, correspo nding to the only limiting factor when pure oxygen is employed as the cathodic reagent. When the oxygen source is air, the diffusion of oxyg en in the gas phase becomes a limiting factor, but for pressurized sys tems the diffusion of water can also be observed, especially for thick membranes. (C) 1998 Elsevier Science Ltd. All rights reserved.