Unveiling stack-level performance heterogeneity in proton exchange membrane fuel cells under elevated temperature and pressure conditions

Variations in single-cell output voltage negatively affect the durability of proton exchange membrane fuel cell (PEMFC) stacks. This study systematically evaluates the temperature distribution, polarization curves, internal impedance, and dynamic performance of a 3 kW-rated PEMFC stack under different operating temperature and pressure conditions, using embedded temperature sensors and electrochemical impedance spectroscopy (EIS). Specifically, the study investigated performance inconsistencies at 95 °C operating temperatures and elevated inlet pressures (250 kPa H₂ and 230 kPa air). The results show that elevated temperatures increase ohmic resistance and deteriorate both voltage and temperature uniformity. At a current density of 2.0 A·cm^-2, the coefficient of variation (C_V) increased from 0.01105 to 0.03779. Conversely, increasing the stack inlet pressure reduces mass transfer resistance, improves output performance, and helps minimize the pressure difference between the inlet and outlet of the reactant gases, thus avoiding the risk of PEM damage and gas crossover. Additionally, during dynamic operation, the stack requires higher operating pressures at elevated temperatures to maintain performance stability under high-load conditions. However, under low- to medium-load conditions, this leads to degraded voltage non-uniformity among individual cells within the stack. This research offers theoretical insights for optimizing PEMFC stack operation under elevated temperature and pressure conditions.