Periodic Tracking of Operando Liquid Water Distributions in PEFCs Subjected to Voltage Cycling Using Micro X-Ray Computed Tomography
Notice bibliographique
Résumé
Low temperature polymer electrolyte fuel cell (LT-PEFC) durability is a key aspect for successful commercialization of this technology. Corrosion of carbonaceous fuel cell components was identified as a major degradation mechanism [1] reducing fuel cell lifetime. Carbon corrosion, which takes place at high local electrochemical potentials in the presence of water, leads to a loss of electrochemical surface area due to detachment and agglomeration of the Pt nanoparticles deposited on the carbon support material as well as loss of electrical pathways. The corrosion induced structural collapse of the cathode catalyst layer (CCL) causes a more tortuous pore space as well as blockage for reactant gas pathways to the catalyst surface and, hence, increased mass transport overpotential. Additionally, the CCL can be made more hydrophilic by addition of oxide surface groups [2]. This can potentially induce changes in gas diffusivity as the CCL becomes more prone to liquid water flooding. Understanding and quantifying the role of liquid water in the various degradation mechanisms is therefore essential for developing novel fuel cell materials and mitigation strategies. In this work, operando lab-based micro X-ray computed tomography (µ-XCT) was applied, for the first time, to track the liquid water distribution in the MEA throughout the lifetime of a fuel cell. This novel methodology is enabled by the non-invasive and non-destructive nature of lab-based XCT [3], allowing multiple identical-location scans at different points in time without interfering with the fuel cell operation or the degradation process. The technique is demonstrated by monitoring the changes in the liquid water distribution within the gas diffusion and catalyst layers of a LT-PEFC subjected to a voltage cycling accelerated stress test designed to induce carbon corrosion. Changes in water accumulation within the porous transport layers as a result of carbon support corrosion are correlated to changes in CCL morphology (thickness and crack size) and CCL composition (Pt/ionomer/carbon content). Representative three dimensional tomography datasets, recorded at beginning-of-life, are shown in Figure 1. The imaging results are further supplemented by electrochemical characterization such as polarization curves, electrochemical surface area (ECSA) and electrochemical impedance spectroscopy (EIS). Highlights of the presentation include the impact of catalyst layer collapse and thinning on liquid water retention behavior of the CCL as well as the effect of increased heat generation on GDL water saturation. Acknowledgments: Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Ballard Power Systems through an Automotive Partnership Canada grant. References: [1] R. Borup, J. Meyers, B. Pivovar, Y.S. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J.E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota, Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K.I. Kimijima, N. Iwashita, Chem. Rev.,107, 3904 (2007). [2] K. H. Kangasniemi, D. A. Condit, and T. D. Jarvi, J. Electrochem. Soc., 151, E125 (2004). [3] R. T. White, M. Najm, M. Dutta, F. P. Orfino, and E. Kjeang, J. Electrochem. Soc., 163 F1206-F1208, (2016). Figure 1. (a) Operando liquid water distribution (blue) and gas diffusion layer structure (light gray) at the cathode. (b) Water (blue), flow field (light gray) and cathode catalyst layer grayscale values in false color including cracks (dark gray). Both images represent a 3D rendering of the segmented phases in perspective projection at BOL (field of view 2.7x2.9 mm2; 750 mA cm-2; 23°C). Figure 1
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Comment cette classification a été obtenuedéplier
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 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| 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 ».