Investigating the Impact of Obstacle Aspect Ratio on Proton Exchange Membrane Fuel Cell Performance: A Comprehensive Numerical and Sensitivity Analysis

In a Proton Exchange Membrane Fuel Cell (PEMFC), the geometry of the flow channels plays a critical role in mass transport, electrochemical current distribution, and water management. The objective of this study is to investigate the effect of the obstacle aspect ratio (AR) in the cathode channel on cell performance under various operating conditions (temperature 333–363 K, pressure 1–4 atm, and anode/cathode relative humidity 0–100%). To this end, a three-dimensional numerical model was developed, and the governing equations for species transport, energy, and electric current were solved using computational fluid dynamics (CFD) with the finite-volume method. The geometric parameters included AR = 0 to 1 for rectangular obstacles in both the cathode and anode channels, and boundary conditions corresponding to temperature, pressure, and humidity were simulated independently. The results showed that intermediate-sized obstacles with AR ≈ 0.25–0.50 significantly enhance oxygen mass transport and reduce concentration losses; for example, at mid-range temperatures (343–353 K) and pressures of 1–2 atm, the power density increased by more than 20%. Specifically, at 343 K and AR = 0.75, the power density rose from 0.3769 to 0.5289 W/cm². At higher pressures (3–4 atm), however, the benefit of small obstacles diminished, and ultimately at 4 atm the obstacle-free configuration (AR = 0) exhibited the highest power density of 0.9134 W/cm². Moreover, AR ≈ 0.25 promoted a more uniform distribution of product water and prevented local water accumulation; as a result, under all humidity levels (0–100% RH) an approximately 15–20% performance improvement was observed compared to the baseline case. These findings provide a foundation for the optimal design of cathode channel geometry in PEMFCs, indicating that AR ≈ 0.25–0.50 covers a wide range of operating conditions with maximum efficiency.