Measurement of O 2 ­ N 2 Effective Diffusivity in Porous Media at High Temperatures Using an Electrochemical Cell

Abstract

The effective diffusivity of in porous media was measured at high temperatures (650-800°C) using an electrochemical concentration cell. Porous membranes having total porosity between 29 and 48 vol% were fabricated from Sr-doped (LSM) with 20 to 30 wt% carbon added as a pore former. The effective binary diffusivity, at 800°C increased from ∼0.016 to ∼0.12 with increasing open porosity between 15 and 44 vol%. The exhibited a nonlinear dependence on open porosity and increased dramatically for samples with greater than 35 vol% open porosity. The estimated effective Knudsen diffusivities of and and at 800°C were an order of magnitude higher than the effective binary diffusivity, Thus, transport through the porous membranes was governed by the effective binary diffusivity, The effects of effective binary diffusivity, on concentration polarization of cathodes for solid oxide fuel cells were assessed. The nonlinear behavior of the effective diffusivity as a function of open porosity indicates that a critical amount of porosity in the cathode is necessary to ensure that the overpotential due to concentration polarization is small. The temperature dependence of was investigated between 650 and 800°C, which was found to be in accord with the Chapman-Enskog model. © 2003 The Electrochemical Society. All rights reserved.