Ni SOLUBILITY IN Ce0.9Zr0.1O2: EXAFS EVIDENCE OF THE FORMATION OF AN AMORPHOUS PHASE OF Ni

JESUS E. VEGA CASTILLO,; MARÍA G. ZIMICZ; FERNANDO D. PRADO; A. CANEIRO

Campinas

Encuentro; 30th LNLS Annual Users? Meeting (RAU); 2020

Cerium dioxide (CeO2, ceria) is one of the materials with widest range of applications.When doping with Zr, resulting materials could be used as active support for anodes ofsolid oxide fuel cells (SOFC), or as active catalysts for methane oxidation [1]. Materialsused as anodes in a SOFC should have a good level of electronic conductivity, and forthat reason many researchers have studied ceria-based anodes with transition metals.Inclusion of transition metals into the crystal lattice of ceria is not a trivial issue. It stronglydepends on preparation method and thermal treatment, and there are somedisagreements in the literature about solubility limits. In this work we analyzed the system(Ce0.9Zr0.1)1-xNixO2-d (x = 0, 0.03, 0.05 y 0.1), with the aim to determine whether Ni isincluded or not into the ceria-zirconia lattice. The crystal structure of the samples wasanalyzed by X-Ray diffraction and by means of HR-TEM (images and elemental mapsof the samples were obtained). The local order of Ni was studied by extended X-rayabsorption fine structure (EXAFS) around the Ni K-edge, in the D08B-XAFS2 beamlineof the Brazilian Synchrotron Light Source (Proposal 20180396). The results of this studygive some insight of the existence of an amorphous phase of Ni in samples with lowcontent of Ni and low temperature thermal treatment. Results of XRD show that thelattice parameter remains constant in all the range of Ni contents analyzed, and there isno evidence of phase segregation for samples calcined at 600ºC and x ≤ 0.05. This issupported by TEM observations, and it was concluded by EXAFS that there is no longrange order. Absorption as a function of wavenumber and Fourier transformed plotsexhibit the typical behaviour of an amorphous phase. Samples heat treated at T 800°Cor with Ni contents higher than 5%mol, exhibit a crystalline NiO phase detected by XRD,HR-TEM and EXAFS.