Decoupling solvents evaporation behavior to reveal the drying mechanism and its effect on microstructure formation of catalyst layer in proton exchange membrane fuel cells.

The drying process is a significant step in catalyst layer (CL) fabrication, and an in-depth understanding is essential to achieve optimal CL structure and cell performance. This study investigates the impact of the solvent evaporation process on CL structure formation as solvent evaporation dominates the CL structure evolution. To decouple the water-alcohol solvent evaporation behavior during slurry drying, a simultaneous mass-loss and heat-flux measurement method is proposed to determine the evaporation rates of components with different vaporization latent heat. The component mass variation and composition evolution are obtained and utilized for drying kinetics and solvent evaporation law analysis. Results indicate that the ethanol evaporates priority over the water, causing the enrichment of the water phase in the coating at the late drying stages, especially at high drying temperatures. The drying temperature is essential for regulating the drying path, which is directly related to the drying rate and affects the CL structure and performance. The CL structural characterizations reveal that low-temperature drying helps form the homogeneous and crack-free CL, while high-temperature drying promotes porosity and large pore proportion. The proposed novel in-situ monitoring method provides an effective approach for revealing the CL drying process. [Display omitted] • A novel in-situ monitoring method is developed to decouple solvents evaporation behavior. • Insights into drying kinetics and compositional evolution of catalyst layer coatings are provided. • The drying path is proved affecting the catalyst layer structure formation. • The impact of drying temperature on CL physical and electrochemical properties is revealed. • Water-phase solvent enrichment is detrimental to catalyst layer formation. [ABSTRACT FROM AUTHOR]