This paper evaluates the liquid water at the gas diffusion layer-channel (GDL-channel) interface of reconstructed GDL microstructures with uniform and non-uniform fiber diameters in wave-like channels. A non-uniform GDL microstructure is reconstructed for the first time at the GDL-channel interface to evaluate droplet motion. The three-layer GDL microstructures are generated using the stochastic technique and implemented using the OpenFOAM computational fluid dynamics (CFD) software (OpenFOAM-6, OpenFOAM Foundation Ltd., London, UK). The present study considers the relationship between reconstructed GDL surfaces with varying fiber diameters, wettability, superficial inlet velocity and droplet size. Results show that the droplet detachment and the average droplet velocity decrease with an increase in the fiber diameter as well as the structural arrangement of the fibers. Under the non-uniform fiber arrangement, the removal rate of water droplets is not significantly improved. However, the choice of smaller fiber diameters facilitates the transport of droplets, as hydrophobicity increases even at slight surface roughness. The results also indicate that the average droplet velocity decreases under low inlet velocity conditions while increasing under high inlet velocity conditions. Therefore, the structural make-up of the GDL-channel interface influences the droplet dynamics, and the implementation of a non-uniform GDL structure should also be considered in the GDL designs.

Metal foam, as a potential alternative to conventional flow fields in proton-exchange membrane fuel cells (PEMFCs), has been adequately proven to possess high gas uniformity and water storage ability. In this study, various cathode flow fields including meatal foam and conventional parallel and serpentine flow fields are compared experimentally. Meanwhile, electrochemical impedance spectroscopy (EIS) is also used to characterize the impedances as a further evidence of water management capacity for different flow fields. The results indicate that the cell with metal foam can achieve up to over 80% power density than that of the serpentine flow field with one third pressure drop. The porosity selection of metal foam is dependent on the inlet relative humidity (RH) to reduce the polarization loss and maximize the cell performance. The inlet relative humidity is also an important factor to the PTFE loading strategy for effective water removal.