Multicomponent Gas Diffusion in Porous Electrodes

Yeqing Fu,John D Pietras,Sophie Poizeau,Martin Z Bazant,Abhijit Dutta,Aravind Mohanram,Yi Jiang

doi:10.1149/2.0911506jes

Abstract

Multicomponent gas transport is investigated with unprecedented precision by AC impedance analysis of porous YSZ anode-supported solid oxide fuel cells. A fuel gas mixture of H2-H2O-N2 is fed to the anode, and impedance data are measured across the range of hydrogen partial pressure (10–100%) for open circuit conditions at three temperatures (800°C, 850°C and 900°C) and for 300 mA applied current at 800°C. For the first time, analytical formulae for the diffusion resistance (Rb) of three standard models of multicomponent gas transport (Fick, Stefan-Maxwell, and Dusty Gas) are derived and tested against the impedance data. The tortuosity is the only fitting parameter since all the diffusion coefficients are known. Only the Dusty Gas Model leads to a remarkable data collapse for over twenty experimental conditions, using a constant tortuosity consistent with permeability measurements and the Bruggeman relation. These results establish the accuracy of the Dusty Gas Model for multicomponent gas diffusion in porous media and confirm the efficacy of electrochemical impedance analysis to precisely determine transport mechanisms.

Highlights

PH02 ONote that in the Rb expressions, there are not too many quantities that need to be fitted to data
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Almost all the variables and parameters are determined from experimental inputs or estimations from kinetic gas theory, except for a microstructure factor, which links effective diffusivity inside porous electrode with its theoretical value

Summary

PH02 O

Note that in the Rb expressions, there are not too many quantities that need to be fitted to data. Almost all the variables and parameters are determined from experimental inputs or estimations from kinetic gas theory, except for a microstructure factor (porosity divided by tortuosity), which links effective diffusivity inside porous electrode with its theoretical value. When the porosity is known, the only quantity need to be determined from fitting is the tortuosity value of the electrodes. Cathode diffusion resistance can be estimated by deriving from a specified diffusion model, e.g., Dusty Gas Model derivation was shown in Eq 19

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Results

Conclusions