Publication

Morphology and Transport Characterization of Catalyst Layers for CO2 Reduction

Résumé

Gas diffusion electrodes (GDEs) help to reduce transport limitations in devices for electrochemical CO2 reduction. Homogenized modeling of such devices requires input of morphological characteristics and effective transport properties of the porous structure, which can be obtained by pore-scale methods. Due to the small pore sizes and layer thicknesses, such characterization of the catalyst layer (CL) is difficult. In this work, CL structures digitalized by FIB-SEM nano-tomography were analyzed to obtain a set of morphological descriptors and were considered as geometrical domains in direct pore-scale simulations to calculate tensors of effective diffusion coefficient, permeability, tortuosity, and effective ionic and electronic conductivity. The CL properties vary significantly depending on the diffusion and flow direction, and samples of similar composition and synthesis technique exhibit different transport behaviors. The reported results provide a quantitative morphological analysis and a reliable set of effective properties to be used in homogenized device modeling, a net improvement over the most commonly used empirical or analytical formulations. The data set was obtained directly from the pore-scale structure of real CLs and contributes to making device-scale homogenized modeling of GDEs more accurate and reliable.

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Concepts associés (34)
Porosité
La porosité est l'ensemble des vides (pores) d'un matériau, ces vides sont remplis par des fluides (liquides ou gaz). Les matériaux poreux sont très généralement des solides, mais il existe aussi des liquides poreux. La porosité est aussi une grandeur physique définie comme le rapport entre le volume des vides et le volume total d'un milieu poreux, sa valeur est comprise entre 0 et 1 (ou, en pourcentage, entre 0 et 100 %) : où : est la porosité, le volume des pores, et le volume total du matériau, c'est-à-dire la somme du volume de solide et du volume des pores.
Diffusion de la matière
La diffusion de la matière, ou diffusion chimique, désigne la tendance naturelle d'un système à rendre uniforme le potentiel chimique de chacune des espèces chimiques qu'il comporte. La diffusion chimique est un phénomène de transport irréversible qui tend à homogénéiser la composition du milieu. Dans le cas d'un mélange binaire et en l'absence des gradients de température et de pression, la diffusion se fait des régions de plus forte concentration vers les régions de concentration moindre.
Porous medium
In materials science, a porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas). The skeletal material is usually a solid, but structures like foams are often also usefully analyzed using concept of porous media. A porous medium is most often characterised by its porosity. Other properties of the medium (e.g.
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