Impacts of the mixed wettability on liquid water and reactant gas transport through the gas diffusion layer of proton exchange membrane fuel cells

In this paper, we develop a pore network model for liquid water and reactant gas transport through the porous gas diffusion layer (GDL) of mixed wettability. We first consider the case of uniform distribution of hydrophilic fraction along the GDL thickness. It is revealed that the addition of hydrophilic pores has a negligible impact on liquid saturation profile when the hydrophilic fraction is low (<= 0.2), whereas in the case of higher hydrophilic fraction (>= 0.4), a flat shape of liquid saturation profile is observed along the GDL thickness. The total liquid saturation in the GDL is found to first decrease and then increase with the increase of hydrophilic pores; and an optimum hydrophilic fraction exists leading to the maximum limiting current density. Also, we investigate the transport process in the GDL of non-uniform wettability (i.e., the hydrophilic fraction is 0.4 near the network inlet, while at the downstream region it is 0.3). As compared to the uniform case, the liquid saturation level at the downstream region is drastically decreased in the non-uniform system, thereby leading to a higher limiting current density. These findings suggest that the fuel cell performance can be improved by designing the GDL with appropriate wettability distribution. (C) 2012 Elsevier Ltd. All rights reserved.