Lattice Boltzmann simulation of a gas diffusion layer with a gradient polytetrafluoroethylene distribution for a proton exchange membrane fuel cell

Abstract

The content and distribution of polytetrafluoroethylene are key factors that determine liquid transport behaviors in gas diffusion layers and, thus, the performance of proton exchange membrane fuel cells. In this study, by employing a stochastic algorithm, the two-dimensional microstructure of a representative gas diffusion layer with the real distributed property of polytetrafluoroethylene was reconstructed. Subsequently, the influence of polytetrafluoroethylene content and gradient distributions on liquid water transport behaviors was examined by implementing a multiphase lattice Boltzmann method. The results supported the findings that an increased content of polytetrafluoroethylene in the conventional gas diffusion layer favors liquid removal, but an extremely high content could cause a marked decrease in the corresponding effective porosity of the gas diffusion layer, hence weakening cell performance. The simulation found that the optimal polytetrafluoroethylene content for the conventional gas diffusion layer was 10 wt%. More importantly, the study reveals that a reasonably higher polytetrafluoroethylene content in the inlet region of the gas diffusion layer benefits the enhancement of water drainage. Compared with the conventional gas diffusion layer with a polytetrafluoroethylene content of 10 wt%, the optimal bigradient and trigradient polytetrafluoroethylene gas diffusion layer exhibits a lower liquid water saturation, a shorter steady-state time of liquid water and gas, and an effective porosity increased by 4.2% and 5.8%, indicating higher water drainage performance. The study here can provide guidelines for the design of high-performance fuel cells with a gradient gas diffusion layer.