Dynamics of Fuel Cell Ink Drying*

Polymer-electrolyte fuel cells (PEFCs) have garnered attention as a replacement for the standard internal combustion engines widely used today. PEFCs avoid the usage of carbon-based fuels and thus release negligible emissions, while being energy dense and efficient. A complex component of the PEFC are the catalyst layers, which comprise a significant portion of the cost of the PEFC and are key for optimizing the utilization of the cell. The catalyst layer includes the catalyst (such as Platinum), typically embedded onto a carbon support along with an ionomer, usually a perfluorosulfonic acid (PFSA), such as Nafion. The fabrication of the catalyst layer involves dispersing the particles into an ink and drying off through a variety of techniques. We will present a detailed discussion of an approach to modeling the interactions between the particles during the drying process and how to control them using adjustable parameters. We propose a drying scheme utilizing convective-driven evaporation where particles increasingly aggregate as the dispersion becomes concentrated until they become gridlocked. From the dried particle network, the bulk properties of the catalyst layer such as the porosity can be obtained. This formulation directly ties the manner in which the catalyst ink is dried off with the structure of the resultant catalyst layer. We compare the predictions against experimental drying processes under a range of conditions. The intuitions gained from this model can help enhance the performance of later generations of PEFCs.