Multicomponent Gas Diffusion in Porous Electrodes

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 H-2-H2O-N-2 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 degrees C, 850 degrees C and 900 degrees C) and for 300 mA applied current at 800 degrees C. For the first time, analytical formulae for the diffusion resistance (R-b) 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. (C) The Author(s) 2015. Published by ECS. All rights reserved.