Numerical Investigations on the Ultrasonic Atomization of Catalyst Inks for Proton Exchange Membrane Fuel Cells

Abstract

In the fabrication of a proton exchange membrane fuel cell electrode, the catalyst layers (CLs) are coated onto either a gas diffusion medium or a membrane. The deposition method of the catalyst ink plays an important role in the structure of the CL, which directly affects its electrochemical performance. Ultrasonic spraying is a method commonly employed for depositing catalyst ink onto the membrane, and the consequent droplet size is correlated to the microstructure of the CLs. In this study, a two-dimensional nozzle model that vibrates at an ultrasonic frequency was developed to simulate the spraying process of the catalyst ink. The volume of the fluid method with dynamic meshing was used. Parametric studies were carried out to gain insights into the atomization process. It was found that measures such as increasing the nozzle amplitude and frequency, and selecting the surface tension and viscosity of the catalyst ink within a proper range, are conducive to obtaining finer droplets and narrower droplet size distribution. Simulation results of non-Newtonian fluids with different viscosity ranges show that the ink fluid with higher viscosity and low shear rate improves the spray quality. This observation is consistent with the results of Newtonian fluids with different viscosities.