Influence of Ink Formulation and Drying Parameters on Component Composition during Drying of Catalyst Layers for Polymer Electrolyte Membrane Fuel Cells and Electrolyzers

The formulation and production of catalyst coatings significantly impact the porous microstructure and the performance of electrodes in polymer electrolyte membrane (PEM) fuel cells and electrolyzers. The critical step in the microstructure formation is the drying. Experimental studies have shown that the drying changes the solvent composition, affecting particle‐ and ionomer (self‐)interactions, as well as ink properties, which influence the drying‐induced stress build‐up within the layers. This study provides a theoretical analysis of the drying of binary 1‐propanol/water mixtures, and the transfer to the drying of catalyst inks. On the basis of selective drying, considering thermodynamic selectivity and gas‐phase kinetics, the accumulation and depletion of solvents during the drying process is described. The influence of different ink formulations (initial solvent compositions) and drying conditions (air temperature, heat transfer coefficient, and air pre‐loading) on ink composition during drying is studied. The selectivity is particularly influenced by the air pre‐loading, for example, relative humidity, which inhibits the evaporation kinetics of water. Theoretical predictions from the drying simulations are experimentally validated via gravimetric drying curves using different catalyst ink formulations. The results suggest that the catalyst layer drying can be effectively modeled by focusing solely on the evaporation dynamics of the solvent mixture.