Pore-level liquid water transport through composite diffusion media of PEMFC

Liquid water transport at the pore level in a composite microporous layer (MPL) and carbon paper gas diffusion layer (GDL), used in a proton exchange membrane fuel cell (PEMFC), has been simulated for the first time by a topologically equivalent pore network (TEPN). Extracted from stochastic generated three-dimensional porous media that replicate typical patterns of void space and fiber connectivity observed in high resolution two-dimensional images of carbon paper GDL and a regular MPL made of carbon black and poly(tetrafluoroethylene), the TEPN for the composite diffusion media is used as input to an invasion percolation flow simulator. Steady-state liquid water distribution and saturation profiles in the MPL-GDL composite media are determined. In the interfacial region between the MPL and the GDL, liquid water saturation increases sharply due to a dramatic change in pore size, confirming the saturation discontinuity modeled in the continuum approach. The effects of current density and MPL thickness on liquid water saturation profiles are also explored. The results suggest that, in contrast to the MPL, liquid water saturation in the GDL is less affected by the current density. A thicker MPL helps to achieve a lower saturation level in the GDL by reducing the number of liquid injection sites into the GDL.