Understanding the liquid water transport behavior in the polymer electrolyte membrane fuel cell gas diffusion layers (GDLs) is essential for improving cell performance and durability. However, the uncontrolled decrease in GDL hydrophobicity has been found within a short portion of the expected operation lifetime. This decreased hydrophobicity can lead to an undesirably high level of liquid water accumulation within the GDL, resulting in performance losses. Furthermore, the impact of the microscale fibre surface morphology on pore-scale liquid water transport is not fully understood. The aim of this thesis is to investigate the impacts of GDL degradation and fibre surface morphology on liquid water transport. Synchrotron X-ray radiography and pore network modeling approaches were employed to perform in situ liquid water visualization and transport modeling, respectively.

An ex situ accelerated carbon-corrosion-based stand-alone GDL degradation procedure was developed. The GDL was degraded as evidenced by a reduction in the GDL contact angle, which was associated with surface corrosion. Next, the impacts of GDL degradation on liquid water distributions were investigated. It was concluded that the increases in liquid water accumulation at component interfaces resulted in the reduced performance, which was attributed to the reduction in GDL hydrophobicity. The contributions of carbon fibre substrate and microporous layer (MPL) degradation were differentiated. The MPL degradation had the most significant impacts on the electrochemical performance and liquid water distributions within the GDL. Lastly, a novel methodology for incorporating fibre surface morphology to simulate liquid water transport in GDLs was presented. This model provides the foundation for future investigations of degradation-influenced liquid water transport at the pore-scale of the GDL. The main findings of this thesis provide new insights into the direct effects of GDL degradation into liquid water transport in the GDL, which are vital for designing next generation GDLs for improved durability.