Investigation on Oxygen Mass Transfer Resistance Mechanism in Fuel Cell Gas Diffusion Layer Under Compression

The significant potential loss of proton exchange membrane fuel cells (PEMFCs) at high current densities is primarily attributed to the high mass transfer resistance of the gas diffusion layer (GDL). The underlying mechanism of how structural parameters of the GDL under actual assembly conditions affect oxygen transport resistance remains unclear, particularly the quantitative relationship between the compression ratio (α) and tortuosity (γ). This study systematically evaluated the output performance and mass transfer overpotential of three commercially available GDLs with similar thickness and porosity under different compression ratios (5.4% to 27%) and four inlet humidity conditions (RH0% to RH100%). By accurately extracting and comparing mass transfer overpotentials, it was observed that the mass transfer overpotential initially decreased and then increased with the rising compression ratio, with an optimum observed at 21.6%. An empirical correlation between the compression ratio (α) and tortuosity (γ) was established as γ = 3.42α + 2.1. Based on this, a modified oxygen diffusion equation was proposed to accurately describe oxygen transport behavior within the GDL under compressed conditions. A modified oxygen diffusion equation was proposed to more accurately characterize the oxygen transport process within compressed GDLs. These findings establish a foundation for optimizing GDL design and stack assembly processes. Future work will build upon this study by incorporating multiphysics conditions such as stack clamping pressure, number of cells, intercell contact resistance, and assembly conditions (temperature and relative humidity), with the aim of elucidating the force–thermal–electrical–mass coupling mechanisms within the stack, thereby enhancing the overall performance and reliability of high-power-density proton exchange membrane fuel cell (PEMFC) stacks.