Pore-scale modeling of gas diffusion layers: Effects of compression on transport properties

A pore-scale simulation approach combining the pore-scale model (PSM) and lattice Boltzmann method (LBM) is developed for a gas diffusion layer (GDL) of a proton exchange membrane fuel cell. The effects of mechanical compression on the transport process of gas species, electric current, heat, and liquid water are studied. A solid mechanics model of the GDL is first numerically reconstructed using a stochastic algorithm. The reconstructed model is then compressed using the explicit dynamics method to generate deformed structures at various compression ratios. PSM simulations are subsequently employed to evaluate the transport properties, and LBM is used to simulate the intrusion process of liquid water and compute the permeability. Simulation results show that electric and thermal conductivities increase with compression ratio, whereas gas diffusivity and water permeability decrease with compression ratio. The in-plane transport properties are found to be greater than the through-plane properties. The anisotropy is evident for electric and thermal conductivities and decreases with increasing compression ratio. The PSM results are substituted into a macroscopic fuel cell model to examine the impact of compression on cell performance. It is found that the local current density becomes more diffusionlimited when the compression ratio is increased.