Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers: Performance Degradation and Steady State Liquid Water Distributions with in Operando Synchrotron X-ray Radiography
Notice bibliographique
Résumé
The polymer electrolyte membrane (PEM) fuel cell is a promising alternative power source for electric vehicles, forklifts, and stationary backup power due to its high power density, low operating temperature, and clean emissions. The gas diffusion layer (GDL) facilitates the transport of heat, reactant gases, water vapor, and liquid water in the PEM fuel cell. The GDL is a highly porous material composed of dense arrays of carbon fibers, resins, and polytetrafluoroethylene (PTFE). Additionally, it is typically coated with a micro porous layer (MPL), which results in the reduction of contact resistance at the catalyst layer interface and the overall improvement in water management. Effective water management must be achieved within the GDL over the entire operating lifetime in order to improve the commercial success of PEM fuel cells. Investigations into the effects of ageing on water management within the GDLs can be useful tools to guide this success. Water is required to maintain polymer electrolyte membrane hydration and ionic conductivity; however, excess water tends to accumulate in the catalyst layer, GDL, and flow channels. This accumulation limits mass transport and leads to performance losses. Therefore, effective water management in the GDLs is essential for improving cell performance, durability, and stability. Most GDL research has been focused on the impact of GDL materials and microstructure design on overall performance, rather than durability. Decreased GDL hydrophobicity has been found after only a few hundred hours of operation (1, 2). Therefore, a clear understanding of the influence of GDL degradation on the liquid water behavior is essential. As a tool to visualize this behaviour, synchrotron X-ray radiography is a powerful technique for visualizing liquid water transport behavior within an operating PEM fuel cell. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were used for identifying liquid water inside the GDLs and capturing the multiphase flow behavior in an operating PEM fuel cell. Figure 1 is an example synchrotron X-ray radiograph of the fuel cell in operando, illustrating the spatial distribution of liquid water. The observed pixel brightness was correlated to the presence of liquid water, and the saturation profile across the GDL thickness was obtained. In this study, as-received fresh GDLs were immersed in a 35wt % solution of H2O2 at 90o C for 12 hours in order to perform an accelerated artificial ageing process. As-received fresh and artificially aged GDLs were then used to assemble specialized fuel cells for synchrotron imaging. Both the electrochemical performance and liquid water transport behavior were observed for a range of current densities. Additionally, the effect of changes in relative humidity on performance was compared to investigate the effect of artificial ageing. Notable differences in cell performance and liquid water transport behavior were observed at steady state operating conditions. The cell with aged GDLs showed lower cell voltage and higher quantities of liquid water than those of as-received fresh GDLs. The impacts of aging on the liquid water distributions within the GDL and on cell performance will be presented in this work. The objective of current work is to highlight the potential degrading effect on liquid water management in long term fuel cell operation. References: 1. S. Kandlikar, M. Garofalo and Z. Lu, Fuel Cells., 11, 6 (2011). 2. P. K. Das, A. Grippin, A. Kwong and A. Z. Weber, J.Electrochem.Soc., 159, 5 (2012). 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 | 0,001 | 0,001 |
| 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 | 0,000 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,001 | 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 ».