Experimental and Simulation Study of Mass Transfer Enhancement by a Foam Microporous Layer in Proton-Exchange Membrane Fuel Cells under a Wide Range of Humidity

Proton-exchange membrane fuel cells (PEMFCs) represent a critical hydrogen-to-electricity conversion technology for clean energy systems. Increasing the power density is a key development priority for broader applications. However, the accumulation of water under high humidity and high current density will limit the mass transfer efficiency of the PEMFC. In this work, a porous foam-like structural microporous layer (MPL) has been fabricated by controlling the distribution of the pore former. When the foam-like MPL is located on the side close to the macroporous substrate, the gas diffusion layer with gradient MPL (GDL-G) exhibits superior performance. Under relative humidity (RH) from 20 to 100%, the average maximum power density of the membrane electrode assembly (MEA) prepared with GDL-G is 1.101 W cm^-2. In comparison to the commercial GDL, the performance improves by 17.9%. Through the electrochemical impedance spectroscopy analysis, it is found that the mass transfer resistance of GDL-G is 37.1% lower than that of commercial GDL under 100% RH. Additionally, GDL-G exhibits lower oxygen mass transfer resistance, demonstrating the rapid diffusion of reactant gases. In combination with numerical simulation, it is found that foam-like MPL has been divided into areas that facilitate the removal of water as well as areas that facilitate the rapid penetration of reactant gases into the catalyst layer. This special form of separate gas-liquid transportation ensures excellent mass transfer efficiency without flooding. Thus, this study not only provides a solution for improving power density under both wide-range humidity conditions and high current density but also offers an in-depth analysis of the gas-liquid two-phase mass transfer mechanisms in GDLs with different structural designs.