Investigation of oxygen transport in porous transport layer with different porosity gradient configurations using phase field method

Minimizing oxygen accumulation in the porous transport layer (PTL) is crucial for reducing mass transfer losses in proton exchange membrane (PEM) electrolyzer. This study develops a two-dimensional transient model of gasliquid two-phase flow at the anode of PEM electrolyzer using the phase field method. The model investigates the mechanisms of oxygen transport and the interactions among various oxygen paths in PEM electrolyzer. We explore the impact of porosity gradient configurations in the PTL and the presence of a surface microporous layer (MPL) on oxygen transport. The findings indicate that for PTL with an average porosity of 60%, forward gradient configuration-where porosity increases from the catalyst layer (CL) towards the channel (CH)-promotes the merging of bubble sites and path contraction, thereby reducing oxygen saturation. The optimal gradient configuration, with porosities of 50% at the CL and 70% at the CH, achieves a 29.5% reduction in oxygen saturation. Conversely, reverse gradient configuration, with decreasing porosity from CL to CH, results in increased oxygen saturation. The addition of surface MPL further lowers oxygen saturation and shortens oxygen breakthrough time; smaller MPL particle sizes correspond to lower oxygen saturation and shorter breakthrough times. This study provides valuable insights for the optimal design of PTL structures in PEM electrolyzers.