Mechanical behavior and properties of gas diffusion layer in proton exchange membrane fuel cells at subzero temperatures

Ice formation in proton exchange membrane fuel cells under subfreezing conditions affects mass and heat transfer in components, causing significant degradation in cell performance and a reduction in cell durability. In this study, the X-ray CT test is conducted, and the microstructure of the gas diffusion layer (GDL) is analyzed and reconstructed. The experimental results show that the porosity distribution of gas diffusion layer is uneven through the thickness direction. Then, the three-dimensional model is established by considering heat transfer, phase change, and mechanical response. The mechanical behavior of gas diffusion layer and the critical transport parameters at subzero temperatures are investigated. The modeling results indicate that the magnitude of displacement decreases with ice content but increases with assembly pressure. At a high ice content and low clamping pressure, the displacement distribution tends to be more uniform. Moreover, with the combined effect of ice formation and clamping pressure in the gas diffusion layer, both the porosity and effective diffusion coefficient show pronounced declining variations with compression ratio, leading to higher mass transfer resistance and severe performance degradation. However, the effective thermal conductivity increases with the compression ratio, indicating the positive effect on heat transfer and more even temperature distribution in gas diffusion layer. These results reveal the profound effect of ice on the transport properties of gas diffusion layer and could be capable of providing a basis for obtaining accurate behavior of the cell.