Modeling of polymer electrolyte membrane fuel cell stack end plates

Good thermal and electric contacts of gas diffusion layers (GDLs) with electrode surface and flow-field plates are important for the performance of a polymer electrolyte membrane fuel cell (PEMFC). These contacts are dependent on the compression pressure applied on the GDL surface. The compression also affects the GDL porosity and permeability, and consequently has an impact on the mass transfer in the GDL. Thus, the compression pressure distribution on the GDL can have a significant effect on the performance and lifetime of a PEMFC stack. Typically, fuel cell stacks are assembled between two end plates, which function as the supporting structure for the unit cells. The rigidity of the stack end plates is crucial to the pressure distribution. In this work, the compression on the GDL with different end plate structures was studied with finite element modeling. The modeling results show that more uniform pressure distributions can be reached if ribbed-plate structures are used instead of the traditional flat plates. Two different materials, steel and aluminum, were compared as end plate materials. With a ribbed aluminum end plate structure and a certain clamping pressure distribution, it was possible to achieve nearly uniform pressure distribution within 10–15 bars. The modeling results were verified with pressure-sensitive film experiments.