Investigation of porous structure formation of catalyst layers for proton exchange membrane fuel cells and their effect on cell performance

The porous structure formation of a catalyst layer used for proton exchange membrane fuel cells was investigated with respect to the control of mass transport in the electrode. The fabrication process involves blending the materials and solvents to form a catalyst slurry, applying the slurry on a substrate, drying to evaporate the solvents, and decal transferring onto the polymer electrolyte membrane by hot pressing. In this study, hot pressing and drying processes were investigated to control the porous structure. The hot-pressing pressure was varied from 0.5 to 10 MPa. The porous structure was evaluated by cross-sectional visualization and a nitrogen physisorption measurement, and it was found that the pressure affects both pore size and porosity. A drastic voltage drop appeared in the polarization curve when the hot-pressing pressure was over 2 MPa. The temperature and humidity during drying were controlled to change the drying rate. The drying behavior was monitored by in-situ visualization and weight measurements. The drying rate slightly affected porosity, although it did not significantly affect the pore size, which was reflected in the polarization curves. These results indicate that the pore size is a more significant factor than the porosity with respect to overpotential in the polarization curve. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.