Surface reaction and transport in mixed conductors with electrochemically-active surfaces: a 2-D numerical study of ceria

Abstract

A two-dimensional, small-bias model has been developed for describing transport through a mixed ionic and electronic conductor (MIEC) with electrochemically-active surfaces, a system of particular relevance to solid oxide fuel cells. Utilizing the h-adaptive finite-element method, we solve the electrochemical potential and flux for both ionic and electronic species in the MIEC, taking the transport properties of Sm 0.15 Ce 0.85 O 1.925Àd (SDC15). In addition to the ionic flux that flows between the two sides of the cell, there are two types of electronic fluxes: (1) cross-plane current that flows in the same general direction as the ionic current, and (2) in-plane current that flows between the catalytically-active MIEC surface and the metal current collectors. From an evaluation of these fluxes, the macroscopic interfacial resistance is decomposed into an electrochemical reaction resistance and an electron diffusion-drift resistance, the latter associated with the in-plane electronic current. Analysis of the experimental data for the interfacial resistance for hydrogen electro-oxidation on SDC15 having either Pt or Au current collectors (W. Lai and S. M. Haile, J. Am. Ceram. Soc., 2005, 88, 2979-2997; W. C. Chueh, W. Lai and S. M. Haile, Solid State Ionics, 2008Ionics, , 179, 1036Ionics, -1041 indicates that surface reaction rather than electron migration is the overall rate-limiting step, and suggests furthermore that the surface reaction rate, which has not been directly measured in the literature, scales with p À1=4 O 2 . The penetration depth for the in-plane electronic current is estimated at 0.6 mm for the experimental conditions of interest to SDC15, and is found to attain a value as high as 4 mm within the broader range of computational conditions.

Evaluation of pulsed laser deposited SrNb0.1Co0.9O3−δ thin films as promising cathodes for intermediate-temperature solid oxide fuel cells

“…To better tune and design cathode materials, ORR mechanisms have been proposed previously [13,42], and are applied to understand ORR on the current thin films. The overall oxygen reduction process can be written as O 2 þ 4e À þ 2V ::…”

Electrochemical behavior of thin-film Sm-doped ceria: insights from the point-contact configuration

“…Beyond this effect, the activity of ceria is known to increase under more reducing conditions, 31,32 serving as an additional reason for the decrease in the resistance associated with the low frequency arc. The change in behavior under bias has somewhat more subtle origins, but is also readily explained.…”

Reducing error and measurement time in impedance spectroscopy using model based optimal experimental design

“…We emphasize that while (2) is expressed in terms of resistances and generalized frequencies, the actual physical parameters we shall investigate (c eon , the concentration of electrons, D eon , the electronic diffusivity, D ion , the ion diffusivity and Z ⊥ ion , the interfacial resistance) can be obtained using Table 1. It has been shown [45] that the electrode resistance is directly related to the porosity of the metal current collector, r A :…”