New insights on the agglomeration and sedimentation behaviours of catalyst ink of proton exchange membrane fuel cells affected by ionomers concentration

The agglomeration and sedimentation behaviours of catalyst ink of proton-exchange membrane fuel cells are vital for the properties of the ink and the formation of the catalyst layer. The ionomers affect the microstructure and interparticle interaction of the ink, subsequently affecting macro-properties. In this study, inks with ionomer-to-carbon (I/C) ratios ranging from 0.25 to 1.25 are evaluated for their particle size, stability, rheology, settling behaviour, and coatability. The particles in all of the inks are weakly linked together to form agglomerates. The I/C ratio reported a direct correlation with the zeta potential and energy barrier of interparticle interactions and an inverse correlation with the strength of the agglomerate network. This is evidenced by the decrease in viscosity and yield stress, which weakens the anti-settling performance. The anti-agglomeration and anti-settling properties exhibit a trade-off relationship depending on the I/C ratio. High viscosities of the ink with an I/C ratio of 0.25 or 0.5 lead to rivulets during slot die coating. In contrast, the ink with an I/C ratio of 0.75 exhibits better anti-settling performance while ensuring coatability and anti-agglomeration properties. These insights contribute to the optimization of ink coatability, and the anti-agglomeration and anti-settling properties, thereby improving the concepts of ink design, and the preparation of the catalyst layer.