Turning Detrimental Effect into Benefits: Enhanced Oxygen Reduction Reaction Activity of Cobalt-Free Perovskites at Intermediate Temperature CO-Induced Surface Activation.

A minor amount of CO in air usually causes a detrimental effect on oxygen activation over a solid oxide fuel cell (SOFC) cathode because insulating surface carbonate is easily formed, which inhibits charge transfer during the oxygen reduction reaction (ORR). In this study, we report that the detrimental effect due to the CO interaction with perovskite oxide can be turned into a beneficial effect for facilitating ORR through tailoring the material composition of the perovskite. More specifically, for cobalt-free SrScNbFeO (SSNF), the exposure to the CO atmosphere results in the formation of a minor amount of surface strontium carbonate mainly in the form of a nanofilm over the perovskite surface, which protects the electrode from further corrosion by CO, thus achieving a relatively stable performance even under a 10% CO-containing air atmosphere. When CO-free air is restored, the SrCO is successfully decomposed at intermediate temperatures. As a result, the surface reaction kinetics is recovered to the initial degree while the charge transfer process is obviously improved. An area-specific resistance of only 0.07 Ω cm is achieved at 650 °C after the CO-induced surface activation, much smaller than the original value of 0.13 Ω cm. In addition, the CO-treated electrode shows a fairly stable performance for ORR under a subsequent CO-free air atmosphere. To create such a beneficial effect, it is critical to tailor the degree of interaction of the perovskite surface with CO, while the benchmark BaSrCoFeO (BSCF) shows a too strong interaction with CO with the formation of bulk-phase-like carbonate, which failed to decomposed even when restored with a CO-free atmosphere at intermediate temperatures, and as a result, worsened the ORR activity after the CO treatment.