Multicomponent Gas Diffusion in Porous Electrodes

TL;DR

This study uses impedance analysis to evaluate multicomponent gas diffusion models in porous electrodes, confirming the Dusty Gas model's accuracy and establishing a precise method to analyze transport mechanisms in solid oxide fuel cells.

Contribution

It derives and tests analytical formulas for diffusion resistance in three models, demonstrating the Dusty Gas model's superior fit across multiple experimental conditions.

Findings

Dusty Gas model provides a consistent fit for all conditions.

Impedance analysis accurately determines transport mechanisms.

Tortuosity is confirmed as the key fitting parameter.

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 (800C, 850C and 900C) and for 300mA applied current at 800C. 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.