Key Role of Interfacial Cobalt Segregation in Stable Low-Resistance Composite Oxygen-Reducing Electrodes

The development of efficient and stable oxygen-reducingelectrodesis challenging but vital for the production of efficient electrochemicalcells. Composite electrodes composed of mixed ionic-electronic conductingLa(1-x )Sr( x )Co(1-y )Fe( y )O(3-& delta;) and ionic conducting doped CeO2 are considered promising components for solid oxide fuelcells. However, no consensus has been reached regarding the reasonsof the good electrode performance, and inconsistent performance hasbeen reported among various research groups. To mitigate the difficultiesrelated to analyzing composite electrodes, this study applied three-terminalcathodic polarization to dense and nanoscale La0.6Sr0.4CoO3-& delta;-Ce0.8Sm0.2O1.9 (LSC-SDC) model electrodes. The criticalfactors determining the performance of the composite electrodes arethe segregation of catalytic cobalt oxides to the electrolyte interfacesand the oxide-ion conducting paths provided by SDC. The addition ofCo(3)O(4) to the LSC-SDC electrode resultedin reduced LSC decomposition; thus, the interfacial and electroderesistances were low and stable. In the Co3O4-added LSC-SDC electrode under cathodic polarization, Co3O4 turned wurtzite-type CoO, which suggested thatthe Co3O4 addition suppressed the decompositionof LSC and, thus, the cathodic bias was maintained from the electrodesurface to electrode-electrolyte interface. This study showsthat cobalt oxide segregation behavior must be considered when discussingthe performance of composite electrodes. Furthermore, by controllingthe segregation process, microstructure, and phase evolution, stablelow-resistance composite oxygen-reducing electrodes can be fabricated.