From optimal uniform-porosity to innovative zoned-porosity design in cathode gas diffusion layer for high-performance air-cooled PEMFCs

To address the challenges of membrane dehydration and mass transport limitations in air-cooled proton exchange membrane fuel cells (PEMFCs), this study focuses on structural optimisation of the cathode gas diffusion layer (CGDL). A three-dimensional, two-phase, non-isothermal numerical model was developed to systematically investigate the influence of uniform porosity CGDL (0.3–0.8) on cell performance. The results indicate that the effect of porosity exhibits significant current density dependence: at low to medium current densities, low-porosity CGDL enhances performance by improving water retention capability and reducing ohmic polarisation; whereas at high current densities, mass transport polarisation becomes the dominant factor, and a CGDL with a porosity of 0.6 demonstrates the best overall performance. Based on these findings and the spatial heterogeneity of water-oxygen distribution within the cell, an innovative in-plane zoned-porosity CGDL strategy is proposed. This design employs low porosity (0.3) CGDL under the flow channel to enhance water retention, and high porosity (0.6) CGDL under the ribs to facilitate oxygen transport. Simulation results show that at a high current density of 1.2 A/cm2, this zoned design increases the cell voltage by 7.43% and 13.07%, respectively, compared to uniform porosity CGDLs with porosities of 0.6 and 0.3. Mechanistic analysis indicates that although the zoned configuration does not maximise either membrane water content or cathode oxygen concentration individually, it maintains both at concurrently high levels and significantly improves current density uniformity, reducing its standard deviation by up to 63.49%. This work provides theoretical insights and a viable design pathway for high-performance, application-tailored GDLs in air-cooled PEMFCs.