Mechanism and kinetics of oxygen reduction on porous La1−xSrxCoO3−δ electrodes

Abstract The linear polarization behavior of La 1− x Sr x CoO 3− δ electrodes has been measured as a function of x , T , and P O 2 using a.c. impedance. These measurements indicate a reaction mechanism in which O 2 is reduced chemically at the porous mixed conductor surface, followed by diffusion of oxygen through the mixed conductor to the electrolyte. Analysis of the electrode kinetics using a recent model for this mechanism yields values for the oxygen vacancy diffusion coefficient ( D v ) and surface-exchange rate constant ( r 0 ) as a function of x , T , and P O 2 . These values agree well with published independent measurements of oxygen chemical diffusion and isotope surface exchange (D and k ). The distance ( δ ) that the reaction extends beyond the electrode/electrolyte interface depends on both D v and r 0 , varying between 0.3 and 10 microns for a typical electrode surface area.

[1]  Y. Takeda,et al.  Cathodic Polarization Phenomena of Perovskite Oxide Electrodes with Stabilized Zirconia , 1987 .

[2]  Henricus J.M. Bouwmeester,et al.  Importance of the surface exchange kinetics as rate limiting step in oxygen permeation through mixed-conducting oxides , 1994 .

[3]  H. Tagawa,et al.  Nonstoichiometry of the perovskite-type oxides La1−xSrxCoO3−δ , 1989 .

[4]  Bouwmeester,et al.  Use of the Rigid Band Formalism to Interpret the Relationship between O Chemical Potential and Electron Concentration in La 1-xSrxCoO3- delta. , 1996, Physical review letters.

[5]  H. Verweij,et al.  Oxygen transport through La1-xSrxFeO3-(delta) membranes. I. Permeation in air/He gradients , 1995 .

[6]  Meilin Liu,et al.  Equivalent Circuit Approximation to Porous Mixed‐Conducting Oxygen Electrodes in Solid‐State Cells , 1998 .

[7]  Henricus J.M. Bouwmeester,et al.  Electrode Properties of Sr‐Doped LaMnO3 on Yttria‐Stabilized Zirconia II. Electrode Kinetics , 1997 .

[8]  B. Abeles,et al.  Diffusion-reaction in mixed ionic-electronic solid oxide membranes with porous electrodes , 1994 .

[9]  Svein Sunde,et al.  Mathematical Modeling of Oxygen Exchange and Transport in Air‐Perovskite‐Yttria‐Stabilized Zirconia Interface Regions II. Direct Exchange of Oxygen Vacancies , 1998 .

[10]  M. Kleitz,et al.  Optimized SOFC electrode microstructure , 1996 .

[11]  Meilin Liu,et al.  Significance of interfaces in solid-state cells with porous electrodes of mixed ionic–electronic conductors , 1998 .

[12]  L. Gauckler,et al.  Electrochemical characteristics of cathodes in solid oxide fuel cells based on ceria electrolytes , 1997 .

[13]  B. Steele,et al.  Properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) double layer cathodes on gadolinium-doped cerium oxide (CGO) electrolytes. I. Role of SiO2 , 1998 .

[14]  Stuart B. Adler,et al.  Electrode Kinetics of Porous Mixed‐Conducting Oxygen Electrodes , 1996 .