Determination of the Rate Constants of Oxygen Reduction in High‐Temperature Air Electrodes on Solid Oxide Electrolytes

The kinetics of electrodes of the type oxygen, noble metal/stabilized zirconia were investigated electrochemically under equilibrium conditions. Single-crystal cubic, polycrystalline cubic, and polycrystalline tetragonal zirconia were chosen as electrolyte materials; platinum and gold were employed as metal components. An electrode setup including a working electrode with a massive metal contact was developed and found to be suitable for well-reproducible long-term measurements. Impedance spectra were recorded in the temperature range from 773 to 1173 K with an oxygen partial pressure range from 1 to 101,325 Pa using a lowexcitation voltage. For platinum, the results indicate a uniform reaction mechanism which involves surface diffusion of dissociatively adsorbed oxygen on the metal surface as rate-determining step. From this, the determination of characteristic thermodynamic data is possible. For gold, the results indicate a change in the reaction mechanism. The results are consistent with one mechanism, in which diffusion limitation of dissociatively adsorbed oxygen on the metal surface occurs, and a competing mechanism, in which transfer limitation of oxygen adsorbed in direct vicinity of the three-phase boundary takes place. The comparison of the different electrolytes does not exhibit significant differences concerning the electrode kinetics.

show abstract

“…-)ka)j " ( Okj) [30] As a first approach, it is assumed that the anodic and cathodic charge-transfer coefficients are equal…”

Section: Discussionmentioning

confidence: 99%

Kinetics of Oxygen, Platinum/Stabilized Zirconia and Oxygen, Gold/Stabilized Zirconia Electrodes under Equilibrium Conditions

Schwandt

Weppner

1997

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…Investigation into the oxygen reduction reaction has shown this to be a complex multistep and possibly multipathway process. [19][20][21][22][23][24][25][26] We have denoted the adsorbed species as a neutral oxygen atom, but it may in fact be partially reduced atomic species as well as the undissociated molecule. For the model formalism it does not matter which species is assumed formed on the surface.…”

Section: Theorymentioning

confidence: 99%

Competition Between Bulk and Surface Pathways in Mixed Ionic Electronic Conducting Oxygen Electrodes

Coffey

Pederson

Rieke

2003

J. Electrochem. Soc.

View full text Add to dashboard Cite

Two parallel pathways have been identified for oxygen reduction and evolution on mixed ionic electronic conductors ͑MIECs͒. Charge transfer may proceed by reaction at the triple-phase boundary to consume or produce oxygen adsorbed on the surface of the MIEC. Alternatively, charge transfer may proceed by reaction of oxygen with oxygen vacancies and electronic holes from the bulk of the MIEC with subsequent exchange of vacancies with the purely ionic conducting electrolyte. A continuum masstransport model is developed describing the competition between these two charge-transfer pathways. Key to the model is treatment of the boundary condition at the MIEC-electrolyte interface. The absolute potential across this interface is used to relate the surface overpotential of each pathway in terms of the other and terms arising from the concentration overpotentials. The current attributable to each of the two pathways can be determined. Results show that the two pathways have different dependence on cell overpotential and competition for reagents creates complex mass-transport dependencies. One pathway may dominate at low overpotentials and the other at high overpotentials. The dependence of current on oxygen partial pressure is shown to transit from ϩ1/2 power dependence to zero or negative power dependence as pressure increases, or to transit from zero or negative to ϩ1/2 power depending on which pathway dominates.

show abstract

“…There are several arguments on the reduction mechanism of oxygen (17)(18)(19)(20), which is important as a determining factor of k'. However, a detailed discussion on the reduction mechanism has been given in a previous paper (21) and hence, in this study, k' will be treated as a parameter to be determined experimentally. Combining Eq.…”

Section: Theoreticalmentioning

confidence: 99%

High Temperature Air Cathodes Containing Ion Conductive Oxides

Kenjo

Osawa

Fujikawa

1991

J. Electrochem. Soc.

157

View full text Add to dashboard Cite

This study is an attempt to improve the performance of Pt/ZrO2 high-temperature air cathodes by imitating porous electrodes of liquid electrolyte fuel cells. Ion conductive oxides were introduced into platinum electrodes in expectation of playing the same electrochemical role as the liquid electrolyte penetrating the porous electrodes. The oxide-mixed platinum electrodes prepared were modeled on a pore whose inner wall was covered with a gas permeable electrolyte film. An analysis based on the pore model predicted that the performance increases with increasing electrode thickness. Electrodes containing (Bi203)0.7 (Er203)0.3 exhibited the expected trend, resulting in a much higher performance than simple Pt/ZrO2 electrodes. However, additions of (ZrO2)0.92(Y203)0.08 or (CeO2)0.8 (SmO1.~)0.2 led to no marked performance improvements. These different effects of oxide additives are explained in terms of the degree of contact between the platinum particles.

show abstract

Determination of the Rate Constants of Oxygen Reduction in High‐Temperature Air Electrodes on Solid Oxide Electrolytes

Cited by 22 publications

References 24 publications

Kinetics of Oxygen, Platinum/Stabilized Zirconia and Oxygen, Gold/Stabilized Zirconia Electrodes under Equilibrium Conditions

Kinetics of Oxygen, Platinum/Stabilized Zirconia and Oxygen, Gold/Stabilized Zirconia Electrodes under Equilibrium Conditions

Competition Between Bulk and Surface Pathways in Mixed Ionic Electronic Conducting Oxygen Electrodes

High Temperature Air Cathodes Containing Ion Conductive Oxides

Contact Info

Product

Resources

About