Observation of Catalyst Layer Structure Formation from Electrode Slurry By White Light Confocal Microscopy

Abstract

Mass transport in the catalyst layers (CLs) is an important factor to improve the cell performance of polymer electrolyte fuel cells (PEFCs). Transport properties in the CLs are determined by their structure and material distributions. The CLs are usually fabricated from electrode slurry in which Pt/C and ionomer are contained through applying and drying processes. Therefore, the structure and material distributions in the CLs are determined in these fabrication processes. However, these fabrication processes have been developed through trial-and-error approaches. A fundamental understanding of the structure formation mechanisms during the fabrication processes is required.The authors have performed impedance measurement and surface displacement measurement of electrode slurry during the drying process at the same time and detected the particle packing process (1, 2). For a further understanding of the fabrication process, observation of the structure formation of electrode slurry during drying by white light confocal microscopy was conducted in this study to break down the structure formation regimes. The observation of flow mode on the surface of the slurry and measurement of surface displacement were performed at the same time.Figure 1 shows confocal images of the electrode slurry during drying. Three different regimes were observed. At the initial state of drying, convection flow was observed. Then, the shrinking of the slurry was observed. After shrinking stopped, the solvent was evaporated from the porous media and finally, the structure of the catalyst layer was formed. Understanding the relationships between the variation of the flow regimes during the drying of electrode slurry and fabrication conditions including materials and process parameters can contribute to revealing the methodology for controlling porous structure and material distributions in the catalyst layers.AcknowledgmentsA part of this work was supported by JST PRESTO JPMJPR22O4.References(1) T. Suzuki et al., ECS Trans., 67(17), 465 (2015).(2) T. Suzuki et al., J. Therm. Sci. Technol., 16(1), 20-00259 (2021). Figure 1