Dynamic thermal and mass transport in PEM fuel cells at elevated temperatures and pressures: A 3D model study

Next-generation proton-exchange membrane fuel cells (PEMFCs) encounter significant challenges at elevated temperatures (OTs) and pressures (OPs) due to local thermal and mass fluctuations. In this study, a three-dimensional transient model was developed to analyze these dynamics by incorporating the effects of the microporous layer and variations in the coolant temperature along the channel. The results indicate that increasing the OT from 80 °C to 90 °C decreases the output voltage by 34–78 mV, increases voltage undershoot/overshoot by 0.2–16.6 mV, and raises the temperature difference between the cathode catalyst layer (cCL) and coolant from 1.2 to 2.1 °C, leading to more irregular temperature fluctuations in the cCL. These effects stem from the increased gas–liquid water outflow within the cCL that induces membrane dehydration, particularly in the electrolyte near the channel. Consequently, the lag in proton conduction relative to the oxygen reduction reaction (ORR), as quantified by the newly introduced Damköhler number, has emerged as a critical factor that influences both heat transfer and reaction kinetics. Conversely, increasing OPs from 130 kPa [anode]/120 kPa [cathode] to 400 kPa [anode]/390 kPa [cathode] improves output voltage by 50–150 mV and reduces proton conduction hysteresis by 12–54 % under dynamic loads. This improvement is linked to higher O₂ concentration and membrane water facilitated by a 0.6–2 °C decrease in cCL temperature. However, the rise in OPs also results in an increased voltage undershoot/overshoot due to greater fluctuations in the membrane water content, ultimately leading to additional power loss. These findings are crucial for optimizing PEMFC performance under extreme conditions and advancing fuel cell technology.