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In this work, several aspects related to the limiting polarization behavior of polymer electrolyte fuel cells were studied using ac impedance spectroscopy. The results were analyzed taking into account the different types of potential losses caused by the interfacial reaction kinetics, the conductance of the electrolyte in the catalyst layer, the oxygen diffusion in the gas phase, in the thin film and in the distributed agglomerate regions of the gas diffusion electrodes and the balance of water in the membrane. The main conclusion is that the water transport in the membrane plays an important role in establishing the limiting polarization behavior of polymer electrolyte fuel cells, corresponding to the only limiting factor when pure oxygen is employed as the cathodic reagent. When the oxygen source is air, the diffusion of oxygen in the gas phase becomes a limiting factor, but for pressurized systems the diffusion of water can also be observed, especially for thick membranes. |
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