Experimental Measurement of Mass Transport Parameters of Gas Diffusion Layer and Catalyst Layer in PEM Fuel Cell

• Author / Creator

  Xu,Hao

• A diffusion bridge is modified to accurately measure the in-plane permeability and diffusivity of gas diffusion layers (GDLs), and to measure the through-plane permeability, effective pore diameter, Knudsen diffusivity and effective diffusivity of catalyst layers (CLs).
  In order to measure in-plane permeability of GDL, nitrogen is injected through the GDL at various flow rates and the pressure drop is measured. Then, Darcy-Forcheimer equation is used to estimate the permeability. The importance of Knudsen slip is estimated by conducting the permeability experiment at various compression levels using different gases. To measure GDL in-plane diffusivity, nitrogen and oxygen are introduced into each channel and oxygen is transported through the sample into the nitrogen channel. The oxygen mole fraction is measured at the outlet of nitrogen channel and the effective diffusivity of the sample is estimated using Fick's first law. Different GDL types are measured to study the effect of carbon matrix and morphology on mass transport properties. Permeability and diffusivity of GDL are found to decrease with volume fraction in matrix. The volume fraction of large pores increases the permeability and diffusivity of GDL. The gas transport properties are dependent on both matrix and pore diameter.
  The CL is fabricated using inkjet printing with varying Nafion loading and effect of ionomer/carbon (I/C) ratio is studied next. The gas-independent permeability and effective pore diameter are obtained using Knudsen's expression. Krypton and carbon dioxide are used for validation. It is shown that Darcy's law is not appropriate and that Knudsen's expression provides accurate results. Nafion loading and I/C ratio are found to have a negative influence on permeability and effective pore diameter. Effective diffusivity is also measured using the same protocol as for GDLs. Nafion loading and I/C ratio are found to reduce the effective diffusivity of CL. Ketjen carbon support CL exhibit better gas transport properties than Vulcan carbon support CL.

• Subjects / Keywords

  • catalyst layer
  • effective diffusivity
  • permeability
  • Knudsen diffusivity
  • gas diffusion layer
  • mass transport

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-r15v-ef66

• License

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