Effects of Solvent Composition on Viscosity and Dispersion Structure of PEFC Catalyst Ink

Structure and performance of PEFC catalyst layer (CL) is greatly influenced by dispersion structure of catalyst ink. Though the solvent composition of the catalyst ink affects the CL performance, correlation between solvent composition, CL structure, and performance has not been fully understood. The purpose of this study was to understand the effects of solvent compositions of the catalyst ink on the dispersion structure, the viscosity characteristics, and the CL structure. Four catalyst inks with different water/ethanol ratio were prepared, and the viscosity characteristics under different shear rate and the particle size distributions were measured without dilution. It was observed that the catalyst ink with higher ethanol ratio had higher viscosity and larger particle size, and it was suggested that decomposition product of ethanol by platinum catalyst affect the viscosity and the dispersion structure of the catalyst ink. Because the aggregates with in the catalyst ink strongly affect the CL structure, it is important to choose the solvent composition.