Characterization of Solvent-Dependent Ink Structure and Catalyst Layer Morphology Based on Ink Sedimentation Dynamics and Catalyst-Ionomer Cast Films

Ink structure is of great research interest because it influences the catalyst layer microstructure and ultimately determines fuel cell performance. To improve understanding of the ink structure, particle size distribution and ink sedimentation dynamics were characterized in this study by performing acoustic spectroscopy (AS) and analytical centrifugation (AC) analyses, respectively, using actual concentrations of Pt/C inks (10.4 wt% of solid content) without dilution. For the catalyst inks prepared with 1-propanol–water bi-solvents of different compositions, the particle size distributions of the inks were similar when a small amount of ionomer (I/C 0.2) was included in the ink. However, the ink sedimentation dynamics showed significantly different results depending on the solvent composition. The different ink dynamics can be explained in terms of the ink structure, and these solvent-dependent ink structures were further studied through the fabrication of catalyst–ionomer cast films. The catalyst agglomeration size and the catalyst–ionomer interfacial structure were effectively observed using scanning electron microscopy (SEM) images obtained from the cast films. The present study reveals the effects of the solvent properties on the structures of ink and catalyst agglomerates. It also demonstrates that the AS and AC techniques can be useful for ink studies.