Dynamics of carbon black particles stabilized by ionomers in catalyst ink by electrophoretic ultrasound scattering

Abstract

Fuel cell catalyst inks are complex materials consisting of (inorganic) carbon black (CB) particles loaded with (metal) platinum catalysts and mixed with (organic) polymers and ionomers for dispersion stabilization. When the microstructure is not easily discriminable by electron microscopy, it is useful to examine the response to dynamic stimuli. In this study, we propose a dynamic ultrasonic analysis to detect the response of particles in suspension to an electric field. Since this method uses ultrasound as the source, it can be analyzed in a lab frame without the use of a large synchrotron radiation facility, and it can be used to analyze optically opaque materials. The proposed electrophoretic dynamic ultrasound scattering method uses a source with a wavelength longer than that of visible light, making it applicable to a wide range of particle sizes, including nanoparticles, submicron particles, and micron-sized particles. Therefore, even if CB particles cannot exist as the smallest primary particles, it has the potential to be applied to the analysis of their aggregates and/or agglomerates. In this study, we show its application to the analysis of Nafion coverage of CB particles in water/alcohol dispersions as an application.