Formulation of carbon black-ionomer dispersions for thin film formation in fuel cells

Abstract The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer. The interactions between the ionomer, carbon black particles, and solvent affect the suspension properties and thus the layer morphology. We analyze the effect of the ionomer-to-carbon ( I / C ) weight ratio for two different types of carbon black on the suspension and layer characteristics. Highly branched carbon blacks with a high surface area tend to form less cracked layers. As less branched carbons can pack together more closely, a smaller pore size results in a larger capillary pressure during drying and thus more cracks. The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles. The carbon black aggregates are thus smaller, resulting in closer packing and thinner layers. Moreover, the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer, preventing crack formation. An optimum I / C weight ratio is identified for optimal layer formation and minimized crack formation.