Analyzing the effects of immobile liquid saturation and spatial wettability variation on liquid water transport in diffusion media of polymer electrolyte fuel cells (PEFCs)

Capillary-induced transport of liquid water inside the porous diffusion media (DM) of polymer electrolyte fuel cells (PEFCs) is strongly dependent on DM pore structure and material properties. As such, excessive liquid in the DM can be expelled more efficiently into flow channels by proper design of the DM structure. The present study is devoted to exploring multiphase transport characteristics by considering the effects of DM pore structure and material properties. Two main effects on overall water removability are examined, namely: (i) the effect of immobile liquid saturation, which is a threshold value for initiating macroscopic capillary transport via connected small liquid droplets, and (ii) the effect of hydrophobic spatial variation, which is encountered in typical DM treated with PTFE. Although these two effects are expected to influence significantly the transport characteristics in the fuel cell DM, they have been ignored in most two-phase fuel cell models reported in the literature. In the present work, these features are implemented into a one-dimensional, multiphase mixture (M2) fuel cell model along the through-plane direction, where both anode and cathode sides and the membrane are fully incorporated. The results of the model simulation clearly demonstrate the dramatic influence of the amount of liquid accumulation and capillary transport characteristics inside the DM. The findings are useful for designing and optimizing DM for the purpose of effective water removal.