Phosphoric Acid Distribution Patterns in High Temperature PEM Fuel Cells

Phosphoric acid plays a major role in the high temperature PEM fuel cell (HT-PEMFC). Phosphoric acid leaching out of the gas diffusion layer (GDL) into the flow field and the exhaust water, however, corrodes the auxiliaries of the stack and complicates water recycling. The distribution of phosphoric acid inside the catalyst layer determines the extent of the triple-phase boundary and thus directly influences the performance of the cell. In this study, phosphoric acid injection experiments and pore network modeling (PNM) were carried out to explain the dependency of phosphoric acid distribution inside HT-PEMFC gas diffusion electrodes (GDE) on different network parameters. PNM was validated for GDEs and used to predict the percolation. We found that the micro-porous layer (MPL) dominates the flow behavior and prevents phosphoric acid from leaching into the GDL. Furthermore, the presence of cracks inside the MPL strongly influences the saturation inside the catalyst layer (CL).