Effect of rheological properties of catalyst slurry on the structure of catalyst layer in PEMFC

Abstract

The dispersion process significantly influences the dispersion of catalyst slurry in proton exchange membrane fuel cells (PEMFCs). The particle size distribution and rheological properties of clusters in slurry directly affect the catalyst layer's coating state, surface morphology, and structure. This paper prepared four different catalyst slurries by high shear emulsification, homogenization, ball milling, and ultrasonic methods. The average particle sizes of clusters in slurry were 725, 337, 452, and 1098 nm, respectively. The rheological properties of catalyst slurry prepared by several dispersion processes are different. Amplitude scanning test demonstrates that yield stresses of slurries prepared by shear, homogenization, ball milling, and ultrasonic methods are 0.047, 0.185, 0.133, and 0.136 Pa, respectively. The viscosity of catalyst slurry is the lowest when prepared by the shear method and is the highest when prepared by the ultrasonic method, and the slurry prepared by homogenization and ball milling methods has the best thixotropy. By observing the catalyst layer, the slurry cluster prepared by the homogenization method has small particles, a strong network structure, and good thixotropy, producing a flat catalyst layer and fewer cracks. Electrochemical tests demonstrate that the catalyst layer with the smoothest surface morphology, the smallest cluster particles, and fewer cracks leads to higher polarization performance. The output voltage of the ink prepared by the homogenization method can reach 0.726 V under the condition of 1000 mA cm−2.