Temperature-induced shear-thinning in catalyst inks
Wataru Yoshimune, Masashi Harada
Abstract
Temperature is a key parameter for ionomer adsorption on carbon supports in catalyst inks for fuel cells, and thus it affects the properties of the ink. This study aimed to investigate the temperature-induced structural evolution and viscosity transition in a catalyst ink. The effect of temperature on the nanostructures of the catalyst ink fabricated from surface-modified carbon supports without platinum nanoparticles was investigated using contrast-variation small-angle neutron scattering (CV-SANS) analysis, through which the concentration and thickness of the adsorbed ionomer layer on the surface of carbon were evaluated. The CV-SANS analysis revealed that the thickness of the shell ionomer layer at 70 °C was twice that at 25 °C, while at elevated temperatures the catalyst ink exhibited shear-thinning behavior. It was surmised that plausible factors in the shear-thinning behavior were a reduction in electrostatic repulsion and the appearance of bridging attraction. Our findings indicate that temperature is a key parameter in the fabrication of catalyst inks, which may be overlooked during the formulation of catalyst inks and catalyst layers.