In order to understand microstructure formation process of the catalyst layer for a polymer electrolyte fuel cell (PEFC), we tried to evaluate the catalyst slurry properties. The catalyst slurries were prepared changing the water/alcohol ratio of the solvent and their flow curve and packing ability were investigated. In addition the size and the adsorbed amount of the ionomer were also measured. On the other hand, the electrode was fabricated from the prepared slurry and its performance was examined.

It was shown that the mean diameter of ionomer measured by dynamic light scattering and the adsorbed amount of ionomer on Pt/C particles decreased with an increase in alcohol ratio of solvent. It was also found that the packing ability of slurry became poorer when the alcohol ratio of solvent increased due to less adsorbed amount of ionomer onto Pt/C particles. From the results of the slurry and the electrode characterization, it was suggested that the adsorbed amount of ionomer and the size of free ionomer could play an important role to improve the PEFC performance.