Hydrodynamic characterization of cathodic flooding in proton exchange membrane fuel cell using a modified Euler number

Flooding is one of the major obstacles to achieve stable performance in Proton exchange membrane fuel cells (PEMFCs). Here, we investigate cathodic flooding using a large-area single cell with in situ visualization. Multiphase flow dynamics are evaluated through synchronized measurements of pressure drop, voltage variation, and water behavior under varying output currents. We introduce a dimensionless parameter, the modified Euler number (
), to quantify the onset and progression of flooding through the balance between air momentum and pressure resistance.
enables distinction between channel flooding and gas diffusion layer (GDL) flooding, providing thresholds based on real-time hydrodynamic and electrochemical responses. At lower currents, water accumulation leads to increased pressure and voltage degradation, while at higher currents, enhanced airflow momentum mitigates blockage through effective droplet removal. Our results show that adjusting the output current indirectly regulates air supply, offering a practical strategy to suppress flooding under air-fed conditions. This airflow-driven mitigation becomes particularly relevant for PEMFCs operating with compressed air rather than pure oxygen. The application of
enables a quantitative understanding of flooding transitions and their performance impact, informing the design and operational control of robust PEMFC systems for potentially advancing vehicle electrification.