Numerical Study of Hydrogen Crossover Evolution Inside the Proton Exchange Membrane Fuel Cell under Dynamic Load

Hydrogen (H₂) crossover in proton exchange membrane fuel cells (PEMFCs) reduces performance and poses safety risks, but its behavior under rapidly changing loads, which are common in vehicles, is not well understood. To address this, we developed a three-dimensional, two-phase, non-isothermal model that tracks H₂ from dissolution in the anode, through transport across the membrane, to reaction at the cathode. The analysis shows that diffusion dominates whereas convection contributes little. Key findings are as follows: H₂ crossover reduces the open-circuit voltage by 210 mV and raises cathode temperature by approximately 0.2°C; reducing the membrane thickness from 20 to 5 μm increases the crossover current density fourfold (from 2.8–3.6 to 11.4–13.2 mA cm⁻²); under rapid load changes, transient undershoots of 0.8–1.72 mA cm⁻² occur because the H₂ concentration drops quickly whereas water and thermal conditions adjust slowly; and a variation of approximately 1 mA cm⁻² along the flow channel indicates that local H₂ distribution and membrane hydration strongly affect transport. Overall, H₂ crossover under dynamic loads is governed by diffusion as modified by local water and heat distribution, with significant differences between channel and rib regions. These results help predict and mitigate fuel cell degradation in practical applications.