Performance Enhancement of Proton Exchange Membrane Fuel Cell Through Synergistic Design of Optimized Gas Diffusion Layer Porosity Distribution and Sinusoidal Flow Field

This study establishes a three-layer porosity gradient optimization framework for the cathode gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs), concurrently considering mass transport, electrical conductivity, and permeability, and systematically investigates its performance under different mass flow rate (stoichiometric ratio) conditions in serpentine and sinusoidal flow fields. The results reveal a pronounced operating-condition dependence of the optimal porosity gradient. At high mass flow rates, where oxygen supply is sufficient and liquid water accumulation becomes the dominant constraint, a mild decreasing porosity distribution (0.6/0.5/0.4) effectively balances oxygen diffusion and water removal. However, as the mass flow rate decreases, oxygen transport resistance gradually becomes the controlling factor in the electrode, requiring enhanced diffusivity and permeability near the catalyst layer. Consequently, a steeper porosity gradient (0.7/0.4/0.4) leads to improved current density. Performance comparisons further demonstrate that applying the optimized three-layer porosity distribution to a serpentine flow field yields a current density enhancement nearly equivalent to that achieved by a sinusoidal serpentine channel with a 0.15 mm amplitude, without requiring structural modifications to the flow channel. This significantly reduces manufacturing complexity and cost while enhancing engineering feasibility. When the optimized porosity is further coupled with the sinusoidal flow field, a synergistic enhancement occurs, where transverse mixing and vertical drainage effects are jointly strengthened, achieving an additional 5-6% increase in current density compared with the conventional uniform GDL. Contour-based analyses confirm that porosity optimization enhances oxygen penetration, promotes liquid water removal, and improves drainage pathways near the catalyst layer, which constitute the key physical mechanisms underlying the performance improvement. Overall, this study proposes a mass-flow-dependent porosity gradient design principle and demonstrates that material-level optimization can partially substitute geometric flow-field redesign under certain conditions, providing a low-cost and highly manufacturable pathway for PEMFC structural optimization.