Quantitative prediction of oxygen diffusion resistance and porous characters under capillary condensation of water in the mesoporous cathode catalyst layer of polymer electrolyte fuel cell*

In the mesoporous cathode catalyst layer of polymer electrolyte fuel cell, water arises as the electrical power generation process goes on through O₂ + 4H⁺ + 4e⁻ -> 2H₂O. It is known that the generated water fills the catalyst layer through capillary condensation that results in a reduction of power generation performance due to a significant increase in the oxygen diffusion resistance, but little is known about the quantitative relation among the oxygen diffusion resistance, the mesoporous characters and the amount of condensed water. A porosity and tortuosity are important parameters to characterize porous structures. In the case of the cathode catalyst layer, the porosity changes through capillary condensation of water and this effect must be considered appropriately. Our group developed coupled analysis simulation of lattice density functional theory and gas transport simulation of Knudsen flow region and applied to the porous media composed of randomly packed spheres [Yoshimoto, Hori, Kinefuchi, and Takagi, Phys. Rev. E, 2017]. In this work, we applied this approach for the actual structure of the mesoporous cathode catalyst layer obtained by scanning electron microscope.