Pore-Scale Saturation and Liquid Water Pathways in PEFCs: Insights from Correlative 2D and 3D X-Ray Imaging
Notice bibliographique
Résumé
Improving the efficiency of polymer electrolyte fuel cells (PEFCs) through high power density operation necessitates liquid water management in the cathode gas diffusion layer (GDL), where liquid water saturation inhibits oxygen diffusivity. To this end, there have been numerous efforts aimed at understanding liquid water transport behaviour to guide GDL design improvements. X-ray imaging of representative in-operando miniaturized PEFC samples has been instrumental to much of recent progress [1–4] in understanding liquid water distribution patterns. Radiographic two-dimensional (2D) images have enabled visualization of liquid water dynamics [3] while three-dimensional (3D) computed tomography images have provided pore-scale information of liquid water saturation states in the GDL [2] and of its transport mechanism [4]. However, how liquid water pathways are formed and the likelihood for preferential pathways remain unclear. In this work, we investigate factors that influence liquid water distribution and pathway definition using correlative rapid 2D and long duration 3D operando X-ray datasets which enable a visualization of liquid water breakthrough dynamics and the corresponding pore-scale interactions in the GDL. The correlated images together with GDL pore structure visualization are used to identify three characteristic pore-scale saturation behaviour with sample regions highlighted in Fig. 1. These regions include locations with restricted liquid water breakthrough, locations with apparent large breakthrough porous pathways where breakthrough liquid water is observable at least in the 2D images, and similarly porous regions where no liquid water breakthrough is observed. It is found that the behaviour shown in the identified regions are strongly linked to local pore-scale structural characteristics and capillary pressure distribution in the GDL. Investigating the 3D virtual GDL from around the microporous layer through to the channel interface, it is shown that liquid water pathways get increasingly defined with a decrease in spatial uniformity towards the flow channels. Pore-scale analysis and observed flow mechanisms show that the defined pathways are locally accessible paths of least capillary resistance dictated by pore radius and associated hydrophobicity. These findings highlight the important role that pore scale topology plays in addition to pore size distribution for future GDL design aimed at improving water management. Keywords— operando, fuel cell, water, pore structure, X-ray imaging Acknowledgments Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, and Canada Research Chairs. References [1] R. T. White, S. H. Eberhardt, Y. Singh, T. Haddow, M. Dutta, F. P. Orfino, and E. Kjeang, “Four-dimensional joint visualization of electrode degradation and liquid water distribution inside operating polymer electrolyte fuel cells,” Scientific reports, vol. 9, no. 1, p. 1843, 2019. [2] H. Xu, M. Bührer, F. Marone, T. J. Schmidt, F. N. Büchi, and J. Eller, “Effects of gas diffusion layer substrates on pefc water management: Part i. operando liquid water saturation and gas diffusion properties,” Journal of The Electrochemical Society, vol. 168, no. 7, p. 074505, 2021. [3] R. Banerjee, N. Ge, J. Lee, M. G. George, S. Chevalier, H. Liu, P. Shrestha, D. Muirhead, and A. Bazylak, “Transient liquid water distributions in polymer electrolyte membrane fuel cell gas diffusion layers observed through in-operando synchrotron x-ray radiography,” Journal of The Electrochemical Society, vol. 164, no. 2, p. F154, 2017. [4] A. Mularczyk, Q. Lin, D. Niblett, A. Vasile, M. J. Blunt, V. Niasar, F. Marone, T. J. Schmidt, F. N. Büchi, and J. Eller, “Operando liquid pressure determination in polymer electrolyte fuel cells,” ACS Applied Materials & Interfaces, vol. 13, no. 29, pp. 34 003–34 011, 2021. Figure 1
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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».