Compréhension de l'impact des harmoniques de courant à haute fréquence sur le vieillissement des piles à combustible à membrane échangeuse de protons

Résumé fourni par la source

In the context of the energy transition, the durability of proton exchange membrane fuel cells (PEMFCs) is a key challenge for their large-scale deployment. This thesis, carried out within the framework of the collaborative HeMoWHy project, investigated the influence of high-frequency current ripples, generated by power electronics, on the degradation mechanisms of PEMFC constituent materials. Accelerated stress tests first confirmed the strong sensitivity of the catalyst to potential variations. The observed degradation mechanisms depend on the potential range: carbon support corrosion occurs at high potential (1.0-1.5 V/RHE), while growth, agglomeration, and/or coalescence of platinum nanoparticles occur at lower potential (0.6‑1.0 V/RHE). In contrast, the membrane appeared relatively stable under these conditions. The effect of potential variation frequency showed that, above 1 Hz, platinum metal-oxide transitions become kinetically limited. To specifically assess the impact of harmonics, a sinusoidal signal with an average current density of 0.8 A·cm⁻² and a 40% peak-to-peak amplitude, with frequencies ranging from 0 Hz (direct current) to 10 kHz, was applied to commercial 25 cm² membrane-electrode assemblies (MEAs) of low-temperature PEMFCs (80 °C) for 500 h. The results indicate that catalyst degradation remains comparable to that observed under constant current conditions. Some membrane degradation was detected, but no clear evidence of a direct link to the harmonics could be established, due to the limited robustness of the membranes tested and the lack of reproducibility in certain experiments. Post-mortem analyses performed on high-temperature PEMFC MEAs (160 °C) subjected to 20 kHz harmonics revealed no specific impact on degradation mechanisms. Overall, the results demonstrate that high-frequency current ripples do not induce additional degradation in PEMFCs, whether operating at low or high temperature. This behavior can be explained by the filtering effect of the electrochemical double layer, which strongly attenuates potential variations at high frequencies (10 kHz). These findings pave the way for simplifying system architectures, in particular by avoiding the need for additional filtering devices dedicated to ripples.

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