About drying phenomena of fuel cell and electrolyzer CCM inks: Selectivity of the evaporation of 1-propanol/water mixtures

Abstract

In the production of catalyst-coated membranes (CCMs) for proton-exchange membrane fuel cells and electrolyzers, the ink formulation and its processing are key factors in determining the resulting catalyst layer. Catalyst inks often contain a multicomponent solvent mixture. Selective drying, which can occur with solvent mixtures, changes the composition in the solidifying film and thus influences the microstructure of the layer that forms. The selectivity depends on the material-specific thermodynamics of the solvents and the process-related drying parameters. Different 1-propanol/water mixtures serve as the state of the art material system considered and commonly used for CCM inks. Typical solvent mixtures can be dried selectively or non-selectively, depending on the initial ink composition and humidity of the drying air. In mixtures that contain more 1-propanol than the azeotropic or arheotropic composition, the 1-propanol content accumulates in the remaining liquid; if there is less, it decreases. Increasing the preloading of the drying air with water leads to a relative water enrichment and shifts the tipping point to higher initial alcohol fractions. This behavior can be transferred to the real CCM production.