Efficient proton exchange membrane fuel cell (PEMFC) operation demands optimization of both flow field geometry and operating parameters to balance mass transport and reaction kinetics. This study quantifies how the aspect ratio (AR) of rectangular flow obstacles interacts with temperature, pressure, and humidity to influence cell performance. A three-dimensional finite-volume CFD model of a full PEMFC, incorporating gas diffusion layers, catalyst layers, and flow channels, was used to solve the coupled transport of species, heat, and current. Rectangular obstacles with AR from 0 (no obstacle) to 1 were placed in the cathode and anode channels, and a design-of-experiments sensitivity analysis was performed over operating conditions: temperature 333–363 K, pressure 1–4 atm, and anode/cathode relative humidity 0–100%. The results reveal that mid-sized obstacles (AR ≈ 0.25–0.50) deliver the largest improvements in power density across all conditions, primarily by enhancing o xygen convection and reducing concentration overpotentials. In particular , AR≈0.25–0.50 configurations provided approximately 18–20% higher power output across a wide range of temperatures and humidity levels on anode and cathode sides, relative to the baseline (AR = 0) case. Peak performance occurred at about 2 atm: under these moderate pressures the obstructed channels achieved maximal power output. However, at 4 atm the trend reversed: diffusion limitations dominated and the obstacle-free design achieved the highest power density. Furthermore, the AR≈0.25 design promoted uniform water distribution and mitigated local flooding, yielding roughly 15–20% gains in performance across the humidity spectrum. These findings map the optimal operating regime and provide guidelines for tuning flow field obstacle geometry to maximize PEMFC performance under realistic conditions.

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