Modeling the performance of electrosprayed catalyst layers in the cathode of polymer electrolyte membrane fuel cells

Catalyst layers produced by electrospray (ES) have shown to be a viable route to improve the performance of polymer electrolyte membrane fuel cells (PEMFCs) due to their good ionic and mass transport properties. In this work, the behavior of ES cathodes is examined numerically for the first time. A model accounting for macroscopic transport in the flow field and in the membrane electrode assembly (MEA) is coupled to a microscopic CL model. The results show that the ES behavior can be explained by a particular multiscale arrangement of liquid water. ES reduces the tortuosity of the ionomer conduction network and promotes water uptake in the ionomer. However, this higher water uptake is accompanied in ES by superhydrophobicity at macroscale (theta(cl) similar or equal to 150 degrees) resulting from the dendritic morphology of the pore surface (Cassie-Baxter type). Superhydrophobicity reduces free liquid water in pores (i.e., liquid water not dissolved in the ionomer), and thereby the oxygen transport resistance. As a result, the performance is improved both under oxygen limiting and self-humidifying conditions. In addition, the optimal ionomer mass fraction of ES is lower than the conventional value (0.15 vs. 0.3) and the ionomer distribution is more uniform, which leads to an improved performance at low Pt loading.