Ink droplet drying analysis for understanding the ink-catalyst layer transition in proton exchange membrane fuel cells

There is still limited understanding of ink structure and the transition process from ink to the catalyst layer (CL) in proton exchange membrane fuel cells despite recent interest in the field. This study proposes a methodology for analyzing the CLs formed after drying single- and multi-ink droplets produced using an ultrasonic spray. Two model inks, Pt/Vulcan Carbon and Pt/Ketjen Black, are prepared using these catalysts, and their characteristics are analyzed through sedimentation behavior, ionomer adsorption quantification, and rheology. The structural properties of the spray-dried CLs are examined using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy-Auger electron spectroscopy. These analyses reveal distinct differences in the CLs' structures, influenced by physical phenomena such as coffee ring formation and droplet coalescence, which are dependent on the ink properties. Furthermore, the structural characteristics of the CLs produced by the two model inks affect the electrochemical behavior of the 25 cm² fuel cell. This study establishes a correlation between the ink structure, CL structure, and fuel cell performance, emphasizing the usefulness of the ultrasonic spray coating method in advancing such investigations.