Selective evaporation of solvent mixtures in thin films for fuel cell and electrolyser catalyst coatings

This study investigates the evaporation of 1-propanol/water solvent mixtures, crucial in the production of catalyst coated membranes (CCM) for fuel cells and electrolyzers. The quantitative determination of the composition of the evaporating solvent mixture is carried out using inverse micro Raman spectroscopy (IMRS). The measurement method and calibration for drying experiments on polymeric-solvent systems presented by Schabel in 2004 is further developed and, for the first time, transferred to a system consisting exclusively of volatile substances and without a nonvolatile reference component. The evaporation process of the micrometer-thin films is measured in situ with high accuracy. Results show selective evaporation, with the 1-propanol enrichment/depletion tipping point at the arheotropic, not azeotropic, composition. Film-side concentration gradients were measured depending on the preferred evaporating solvent. Initial experiments incorporating an industrially relevant ionomer demonstrate its effect on the evaporation selectivity. A roadmap for further understanding mass transport processes in catalyst inks is presented.