Comparative analysis of degradation mechanisms in HT-PEM fuel cells under start–stop and load cycling with hydrogen and nitrogen-diluted feeds
Mengfan Zhou, Na Li, Deyong Wang, Samuel Simon Araya, Vincenzo Liso
Abstract
The integration of reformers into high-temperature polymer electrolyte membrane (HT-PEM) fuel cells presents a significant opportunity to improve fuel flexibility and cost-effectiveness. To understand their degradation, we applied two start–stop cycling procedures: one with pure H2 and another with an 80 vol % H2 and 20 vol % N2 mix to simulate reformate gas. We also performed a load cycling test with H2 as anode gas. The results indicated that degradation rate of pure H2 start–stop cycling showed 306 μV h−1, while load cycling demonstrated a degradation rate of 19.7 μV h−1 for the current density of 0.2 A cm−2, and 88.2 μV h−1 for the current density of 0.4 A cm−2. Start–stop cycling with diluted gas resulted in a constant voltage drop with a degradation rate of 3.129 mV h−1. Electrochemical impedance spectroscopy (EIS) indicated an increased ohmic resistance during start–stop cycling and higher charge transfer (high-frequency) and mass transport (low-frequency) resistance with nitrogen introduction. Scanning electron microscope results confirmed MEA degradation. In conclusion, start–stop cycling and anode gas dilution are stressors that accelerate HT-PEM fuel cell degradation, reducing its lifetime.