Effect of Dispersion Method and Catalyst on the Crack Morphology and Performance of Catalyst Layer of PEMFC

The effects of dispersion method for ink preparation and types of catalyst on the catalyst layer's structure and characteristics were investigated. Catalyst layers prepared by two dispersion methods, i.e., sonication and ball-milling, and two types of catalyst: Pt-HSC (High Surface Area) and Pt-Vulcan XC-72, were fabricated. Viscosity, particle size distribution of the catalyst inks, catalyst layer's surface properties, and cell performance were measured. Experimental results with the Pt-HSC at ionomer/carbon weight ratio 0.8 show that ink dispersity strongly depends on the mixing method and large agglomerates form in the ink after sonication. The effect of the dispersion method on the ink prepared by Pt-Vulcan XC-72 at similar conditions is not noticeable. The catalyst layer's mechanical properties, such as hardness and Young's modulus, were found to vary widely. With an increase of catalyst layer thickness, the number of pin-holes decreased and cracks gradually increased in size. Polarization curves show that the membrane electrode assemblies (MEAs) made with 60% Pt-HSC have a better performance than those with 30% Pt-Vulcan XC-72. The performance and measured electrochemical active surface area of the MEAs made from both catalysts are slightly affected by dispersion method.