  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.
