High Temperature Air Cathodes Containing Ion Conductive Oxides

Abstract

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.

The role of electrode microstructure on activation and concentration polarizations in solid oxide fuel cells

“…These observations are at ary (TPB) at the surface of the electrocatalyst/dense variance with the predictions of the model by Kenjo electrolyte membrane (e.g. LSM and the dense YSZ et al [7]. However, their results are entirely conmembrane) contributes to the charge transfer resistent with the model presented by Tanner et al action; hence the presence of V, in the denominator…”

“…With a 10 pxm thick YSZ film as the electrolyte, the The role of composite electrodes, comprising a area specific resistance of the electrolyte is only mixture of a solid electrolyte and an electronic about 0.05 fjcm 2 at 800N C thus making an efficient conductor, or a mixed ionic-electronically conductoperation of an SOFC at such a low temperature in ing (MIEC) material, on electrode kinetics has been principle possible. However, it is usually observed examined by a number of researchers [7][8][9][10][11]. The that despite a low ohmic contribution, the area rationale for the use of a composite or an MIEC electrode is that it allows a spreading of the reaction RT zone from the electrolyte/electrode interface into the act -zF i = R,,i (2) electrode.…”

Active Cathodes for Super-High Power Density Solid Oxide Fuel Cells Through Space Charge Effects

“…Note that there are no terms containing I e in Eq. (37). However, it is important to note that I e is not zero, although usually |I e | |I i | in the present case of fuel cells.…”

“…Recent work has shown that cathodic polarization can be substantially reduced provided the porous cathode is mixed conducting [37][38][39][40]. For this reason, the cathode must either be made of a single-phase MIEC material, or a composite mixture of an oxygen ion conductor (e.g.…”

Active Cathodes for Super-High Power Density Solid Oxide Fuel Cells Through Space Charge Effects

“…Effort was directed in three areas: (1) Further development of the model on the role of connectivity on ionic conductivity of porous bodies, including the role of grain boundaries and space charge region. (2) Calculation of the effect of space charge and morphology of porous bodies on the effective charge transfer resistance of porous composite cathodes.…”