Formation of Liquid Water Pathways in PEM Fuel Cells: A 3-D Pore-Scale Perspective

Abstract

We investigated the 3-D pore-scale liquid water distribution within the cathode GDL via in operando synchrotron X-ray tomography during low current density fuel cell operation to capture the early appearance of liquid water pathways. We found that the invasion of liquid water into the GDL only partially filled certain GDL pores. Liquid water preferentially flowed along some GDL fibers, which was attributed to the hydrophilic nature of carbon fiber and the presence of pore-scale mixed wettability within the GDLs.

Discrete-Particle Model to Optimize Operational Conditions of Proton-Exchange Membrane Fuel-Cell Gas Channels

“…The water cluster density in PEFC GDL was estimated from the published images in μCT studies. The water cluster density (n mm –2 ) was estimated at different current densities available from three different sources. ,,, Two additional VoF simulations were performed on μCT images of Toray (Toray TGP-H 060) and SGL (SGL 25 BA) materials for a full-area water injection to estimate the average cluster density, with cluster visualizations shown in Figure a. The VoF simulations represented an ex situ scenario, and therefore, the results do not represent a current density value.…”

“…Droplets emerge into the channel at locations and rates determined by the distribution of water clusters within the GDL. ,,,, Micro X-ray-computed tomography (μCT) experiments show the formation of discrete water clusters in the GDL ,, and spherical droplets on the GDL surface in the channel . Therefore, the water injection rate is into each droplet is specified by the water source velocity u w i or by the operating current based on the available active area ( WL )­ where I is the current and M w is the molecular mass of water.…”

Degradation Characteristics of Electrospun Gas Diffusion Layers with Custom Pore Structures for Polymer Electrolyte Membrane Fuel Cells

“…The fluorination procedure was starkly different from typical PTFE coating procedures used to render commercial GDL materials hydrophobic. Commercial coating procedures lead to an uncontrolled and nonhomogeneous dispersion of PTFE through the GDL, thereby altering the pore structure and water transport properties of the carbon substrate. ,− The uncontrolled alteration of the pore structure is undesirable for electrospun GDLs, as the custom tailored pore structures could be unintentionally modified to hinder water and reactant transport. Therefore, hydrophobicity treatments that induce minimal morphological alterations, such as the direct fluorination treatment as opposed to PTFE coating procedures, are necessary and vital for the development of electrospun GDLs with custom, specified pore structures.…”

“…Throughout the 6000 h of operation, they observed increases in mass transport losses and attributed the losses to the oxidation of the GDL fibers (observed post-mortem) associated with liquid water accumulation. The oxidation of the GDL fibers led to a loss of hydrophobicity, ineffective liquid water removal, and consequently reduced fuel cell performance . Although in situ drive-cycle tests are insightful, the tests take a considerable amount of time, making them impractical for the rapid development of new materials such as the eGDLs. , …”

“…The oxidation of the GDL fibers led to a loss of hydrophobicity, ineffective liquid water removal, and consequently reduced fuel cell performance. 14 Although in situ drive-cycle tests are insightful, the tests take a considerable amount of time, making them impractical for the rapid development of new materials such as the eGDLs. 15,26 To minimize the testing times required for degradation studies, in situ accelerated degradation testing protocols (i.e., test conditions that enhance/accelerate the degradation of fuel cell components) have been employed.…”