Effects of Nafion impregnation on performances of PEMFC electrodes

The effect of Nafion loading on the electrode polarization characteristics of a conventional proton exchange membrane (PEM) fuel cell electrode has been investigated in terms of both H-2/O-2 and H-2/air performance. Correlation of Nafion loading with the activation polarization characteristics shows an initial increase of activity upto a loading of 1.3 mg/cm(2) followed by a more gradual change with maxima at 1.9 mg/cm2 for both oxygen and air. This trend correlated well with the decrease in charge transfer resistance and increase in the electrochemically active surface area. The contributions to the linear ohmic polarization region of both the H-2/O-2 and H-2/air performance are predominantly from ionic resistance as well as diffusional contributions in the catalyst layer. Among all the polarization losses those due to mass transport were the highest. Fits using a thin film agglomerate model showed a rapid increase in the film thickness with Nafion loading in the pores of the carbon of the catalyst layer followed by an equilibrium of similar to 800 Angstrom thickness at a Nafion loading of 1.9 mg/cm(2). Further additions caused deeper penetration of this Nafion film into the catalyst layer increasing the diffusional pathways for the reactant gases. These results correlate well with the mass transport characteristics in O-2 and air as well as morphological characterization of the electrode based on SEM and pore volume distributions. (C) 1998 Elsevier Science Ltd. All rights reserved.