Hierarchical Interfaces Structure Enabling Adaptive Gas–Liquid Transport under Wide Humidity Ranges in PEMFC Microporous Layers

Achieving excellent water management capabilities under wide humidity ranges plays a crucial role in enhancing the performance of proton exchange membrane fuel cells (PEMFCs). Modifying the structure of the microporous layer (MPL) is one of the important strategies. In this study, a hierarchical interface structure MPL featuring a flat, dense surface and perforations is prepared. The results indicate that the MPL with a hierarchical interface structure demonstrates superior performance across a wide range of humidity. Its power density at 2 A/cm² is 12% higher than that of the normal MPL. The hierarchical interface structure significantly decreases the oxygen transport resistance (OTR) and expands the dry region from 1 A/cm² to 1.5 A/cm². A millimeter-scale Lattice Boltzmann Method (LBM) simulation, in conjunction with experiments, systematically demonstrated the water management mechanisms of the hierarchical interface structure across a wide range of humidity. At low humidity, the dense regions retain moisture within the membrane, while the perforation promotes the molecular diffusion of gases. At high humidity, perforations become the preferred conduction pathways for liquid water, and the dense regions enhance this effect, thereby reducing the water saturation in each layer within the gas diffusion layer (GDL). This work proposes a design strategy for MPLs aimed at achieving effective water management. The findings enhance our understanding of gas-liquid transport behavior within pores of varying sizes across a wide humidity range.