Knudsen Diffusivity and Permeability of PEMFC Microporous Coated Gas Diffusion Layers for Different Polytetrafluoroethylene Loadings

The Knudsen diffusivity and viscous permeability of proton exchange membrane fuel cell microporous coated gas diffusion layers are obtained experimentally for different polytetrafluoroethylene loadings. Pressure drop across the microporous coated gas diffusion layers is measured at varying flow rates and using different gases. A semi-empirical expression proposed by Knudsen is used to analyze the experimental results and is shown to accurately predict gas transport in microporous coated gas diffusion layers. The Knudsen diffusivity of the microporous coated gas diffusion layers is shown to decrease with increased PTFE loading. The compressible form of Darcy's law is shown to overestimate the viscous permeability of microporous coated gas diffusion layers because it cannot account for gas slip at the pore walls.