Nanostructured La1xSrxCo1-yFey0.03Pd0.03O3d (LSCF-Pd) perovskites with fixed La-Sr composition (x = 0.4) and two different Fe contents (y = 0.2 and 0.8) were successfully synthesized using a one pot citrate method starting from nitrates of the metal cations. Pd-free La1xSrxCo1yFeyO3d (LSCF) systems were prepared for comparison. LSCF powders were calcined at 1300 1C and characterized by XRD and Rietveld refinement, EXAFS, XPS, TPR analyses. Promotion of La0.6Sr0.4Co0.8Fe0.2O3d and of La0.6Sr0.4Co0.2Fe0.8O3d by incorporation of palladium was evidenced by solving the local environment of Pd using EXAFS spectroscopy. XPS analyses, in agreement with TPR measurements, demonstrated an increase of superficial oxygen vacancies, the variation being much more pronounced in the La0.6Sr0.4Co0.8Fe0.17Pd0.03O3d sample. It is argued that this increase is associated with the introduction of Pd in the B site of LSCF. Moreover, ionic Pd4+ was detected as the only palladium species on the perovskite surface, whereas Pd metal clusters of about 2 nm, not detectable in the surface, are embedded in the matrix and strongly interact with the bulk. This result has strong consequences in the synthesis and in the design of new perovskite materials that can be used as cathodes in fuel cell application at intermediate operating temperatures.
Palladium local structure of La1-xSrxCo1-yFey-0.03Pd0.03O3-? perovskites synthesized using a one pot citrate method
F Puleo;L F Liotta;V La Parola;
2014
Abstract
Nanostructured La1xSrxCo1-yFey0.03Pd0.03O3d (LSCF-Pd) perovskites with fixed La-Sr composition (x = 0.4) and two different Fe contents (y = 0.2 and 0.8) were successfully synthesized using a one pot citrate method starting from nitrates of the metal cations. Pd-free La1xSrxCo1yFeyO3d (LSCF) systems were prepared for comparison. LSCF powders were calcined at 1300 1C and characterized by XRD and Rietveld refinement, EXAFS, XPS, TPR analyses. Promotion of La0.6Sr0.4Co0.8Fe0.2O3d and of La0.6Sr0.4Co0.2Fe0.8O3d by incorporation of palladium was evidenced by solving the local environment of Pd using EXAFS spectroscopy. XPS analyses, in agreement with TPR measurements, demonstrated an increase of superficial oxygen vacancies, the variation being much more pronounced in the La0.6Sr0.4Co0.8Fe0.17Pd0.03O3d sample. It is argued that this increase is associated with the introduction of Pd in the B site of LSCF. Moreover, ionic Pd4+ was detected as the only palladium species on the perovskite surface, whereas Pd metal clusters of about 2 nm, not detectable in the surface, are embedded in the matrix and strongly interact with the bulk. This result has strong consequences in the synthesis and in the design of new perovskite materials that can be used as cathodes in fuel cell application at intermediate operating temperatures.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
