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3D characterization of diffusivities and its impact on mass flux and concentration overpotential in SOFC anodes

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Title: 3D characterization of diffusivities and its impact on mass flux and concentration overpotential in SOFC anodes
Authors: Lu, X
Tjaden, B
Bertei, A
Li, T
Li, K
Brett, D
Shearing, P
Item Type: Journal Article
Abstract: In recent years great effort has been taken to understand the effect of gas transport on the performance of electrochemical devices. This study aims to characterize the diffusion regimes and the possible inaccuracies of the mass transport calculation in Solid Oxide Fuel Cell (SOFC) anodes when a volume-averaged pore diameter is used. 3D pore size distribution is measured based on the extracted pore phase from an X-ray CT scan, which is further used for the calculation of a Knudsen number (Kn) map in the porous medium, followed by the voxel-based distribution of the effective diffusion coefficients for different fuel gases. Diffusion fluxes in a binary gas mixture using the lower boundary, upper boundary and average effective coefficients are compared, and the impact on overpotential is analyzed. The results show that pore diameters from tens to hundreds of nanometers result in a broad range of Knudsen number (1.1 ∼ 4.8 and 0.6 ∼ 3 for H2 and CH4 respectively), indicative of the transitional diffusion regime. The results highlight that for a porous material, such as an SOFC anode where Knudsen effects are non-negligible, using a volume-averaged pore size can overestimate the mass flux by ±200% compared to the actual value. The characteristic pore size should be chosen sensibly in order to improve the reliability of the mass transport and electrochemical performance evaluation.
Issue Date: 21-Jan-2017
Date of Acceptance: 6-Jan-2017
URI: http://hdl.handle.net/10044/1/43821
DOI: https://dx.doi.org/10.1149/2.0111704jes
ISSN: 0013-4651
Publisher: Electrochemical Society
Start Page: F188
End Page: F195
Journal / Book Title: Journal of the Electrochemical Society
Volume: 164
Issue: 4
Copyright Statement: © The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited.
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Commission of the European Communities
Funder's Grant Number: EP/M014045/1
Keywords: Energy
0303 Macromolecular And Materials Chemistry
0306 Physical Chemistry (Incl. Structural)
0912 Materials Engineering
Publication Status: Published
Appears in Collections:Earth Science and Engineering
Faculty of Engineering