Résumé
Polymer Electrolyte Membrane Fuel Cells (PEMFC) are considered the most mature technology for both passenger and heavy-duty hydrogen vehicles. Nonetheless, fundamental and applicative research is still necessary to overcome some technical barriers, especially the durability issues. One of the most relevant contributors to the performance loss is the degradation of the catalyst nanoparticles (NPs) of the cathode catalyst layer. During operation, characterized by thousands of operating hours under a variable load, Pt is unstable in the acidic environment.This work refines a previously proposed catalyst degradation model for PEMFCs1, which accounts for the oxidation/reduction of Pt nanoparticles, as well as of Pt dissolution/redeposition. The model is particularly useful for predicting the loss of electrochemically active surface area (ECSA) over extended operating periods. Two state-of-the-art catalyst coated membranes (CCMs) were analysed and the predictions were validated against a comprehensive dataset2 covering voltage profiles relevant to PEMFC operation in the transportation sector. These profiles span from 0 V—representative of short-stop conditions—up to 0.85–0.90 V. A key feature of the model is the incorporation of the interplay between Pt place-exchange oxide reduction and dissolution during low-voltage transients. Notably, a new mechanism is proposed3 to explain an ECSA loss contribution that was experimentally observed but remains unaccounted for in existing models. Operando synchrotron high-energy wide-angle X-ray scattering (WAXS)4 was employed to analyse the same CCMs under both H₂/N₂ and H₂/diluted air conditions. By tracking scattering intensity and surface crystallinity5, the formation and reduction of stable oxides were investigated while varying the upper potential limit and the holding times. In the modeling approach, these stable oxides are assumed to form preferentially at the most oxophilic sites—such as edges, corners, etc.—which are prevalent in smaller nanoparticles and at the beginning of life. The model also differentiates oxide removal behaviour at 0.6 V compared to 0.2 V and 0.067 V, as observed in the WAXS analysis, and links the latter to a concurrent cathodic platinum dissolution process. This low-potential region facilitates rapid Pt ion redeposition rather than diffusion towards the membrane, preferentially leading to NP growth. Consistently, post-mortem transmission electron microscopy (TEM) analyses revealed large, highly spherical nanoparticles but no significant Pt band in the membrane. TEM images of CCMs aged under voltage profiles with different lowest potentials were also compared. Overall, this work proposes a physic-based interpretation of real-world electrocatalyst aging phenomena, aiming to comprehensively interpret the role of low potential transients in ECSA loss.This work received support from “Progetto Permanent - Bando Mite PNRR Missione 2 Investimento 3.5 A-RSH2A_0O0012”. WAXS data were collected in the experimental session MA-6091 at ID31 beamline of the European Synchrotron Radiation Facility (https://doi.org/10.15151/ESRF-ES-1550921429). T. Jahnke, A. Baricci, C. Rabissi, and A. Casalegno, J. Electrochem. Soc., 167, 149001 (2020).E. Colombo, A. Casalegno, L. Guetaz, and A. Baricci, Int. J. Hydrogen Energy, 65, 292–307 (2024).E. Colombo et al 2023 Meet. Abstr. MA2023-02 1976.O. M. Magnussen, J. Drnec, C. Qiu, I. Martens, J. J. Huang, R. Chattot, and A. Singer, Chem. Rev., 124, 629−721 (2024).C. A. Campos-Roldán, A. Gasmi, M. Ennaji, M. Stodel, I. Martens, J.-S. Filhol, P.-Y. Blanchard, S. Cavaliere, D. Jones, J. Drnec, and R. Chattot, Nat. Commun., 16, 936 (2025).