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.

This paper reports on the development of a novel approach to investigate the stress and strain distributions at the fiber's scale of PEMFC gas diffusion layers (GDLs). The present method includes stochastic reconstruction and finite element solution procedure. The microstructure of a GDL was randomly generated and meshed, upon which solid mechanics simulations were performed. Stress and strain distributions in three dimensions were obtained by considering dynamic contact, frictional motion and extruding deformation of the fibers. A sensitivity analysis on the present model showed that frictional coefficient between fibers has more influence on the model results than the mechanical properties of the fiber. Our simulation results show that under compression, the fiber's displacement in the through-plane direction is significantly more than the in-plane direction. Fibers intruding into the gas channel were also observed. For the case with 20% compression ratio, the computed stress is mostly below 100 kPa with a maximum in excess of 1,000 kPa. Simulation results, which include stress and displacement distributions under compression, are in qualitative agreement with actual observations in the literature. The present methodology can be extended to most porous electrodes that involve material deformation to allow accurate evaluation of their transport properties and performance.