Mixed cathode channel opening ratios for improved thermal uniformity at comparable peak power in fan-cooled open-cathode PEMFC stacks

Open-cathode polymer electrolyte membrane fuel cells (PEMFCs) cooled by a single fan inherently suffer from cell-to-cell non-uniformities in cathode air supply that couple reactant access, membrane hydration, and heat removal. Existing studies optimize the cathode channel as a single uniform geometry across the entire stack and therefore cannot address the spatially varying thermal-hydration demands intrinsic to fan-cooled operation. This study proposes mixed-opening ratio cathode channels that intentionally vary the per-cell opening ratio along the stack axis to break this single-geometry constraint. Three cathode flow-field plates with opening ratios of 50%, 61.25%, and 70% (Types A, B, C) were fabricated as a design library and characterized in single-cell tests, which quantified a hydration-transport trade-off that reverses between low and high current density. A coupled flow-electrochemical-thermal model was developed and validated against five-cell-stack polarization and per-cell temperature data for the three uniform configurations, and was then used to screen 27 symmetric mixed layouts under fan-cooled boundary conditions. A center-moderated layout, 70-70-61.25-70-70 (CCBCC), was identified as the Pareto-optimal design within the screened set and verified experimentally: it reached a measured peak power of 77.1 W, comparable to (3.8% above) the best uniform stack (BBBBB, 74.2 W), while reducing the cell-temperature standard deviation from 2.80 °C to 2.27 °C (−19%) and lowering the stack-average temperature by 2.2 °C. The model reproduced the measured peak-power ranking of all six tested stacks. Replacing the Type B plates at the four outer positions with Type C plates raises the predicted fan airflow by 5%, and the measured profiles show that the cooling gain is largest in the hottest interior cells. Because the gain is obtained only by assigning the existing plate types to different stack positions, without additional balance-of-plant components, the approach offers a low-cost route to more uniform and potentially longer-lived fan-cooled fuel-cell power sources for drones and portable devices.