Abstract
Voltage instability in proton exchange membrane fuel cells (PEMFCs) under flooding conditions arises from complex, coupled operating conditions. Comprehensive experimental characterization across this domain is resource-intensive, which hinders systematic optimization. To address this challenge, this paper proposes a dimensionality reduction framework for characterizing voltage behavior. Firstly, an index based on cathode outlet oxygen partial pressure is introduced to describe mean voltage. Secondly, a balance parameter (Φ) for water accumulation and removal is formulated to characterize the voltage oscillation amplitude, incorporating both removal via aerodynamic shear and evaporation. The method was validated on a 10-cell PEMFC stack under 198 steady-state operating conditions, covering stoichiometric ratios of 1.5–2.0, outlet pressure of 40–140 kPa, and relative humidity of 60–100%. Results demonstrate that mean voltage and voltage oscillation collapse onto unified trends when mapped onto these two indices, with correlation coefficients exceeding 0.8. Furthermore, deviation analysis reveals that mean voltage index errors originate from liquid water obstructing oxygen transport, while errors in the oscillation index arise from flow regime transitions that reduce evaporative efficiency at low stoichiometry. Additional analysis elucidates the non-monotonic effects of pressure and humidity on the voltage oscillation amplitude. Unlike data-driven or invasive methods, this framework relies solely on externally measurable variables to reveal operating space redundancy, enabling real-time diagnosis and control without internal sensors or computationally intensive simulations.
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•Two indices from external signals fully characterize PEMFC flooding voltage behavior.•Oxygen partial pressure at cathode outlet predicts mean voltage across conditions.•Water-balance parameter Φ captures voltage oscillation amplitude across conditions.•Experiment validates two proposed indices across 198 conditions with R ≫ 0.8.•Non-monotonic pressure effect on oscillation is revealed at constant stoichiometry.