Exploration of Atomic Scale Changes during Oxygen Vacancy Dissociation Mechanism in Nanostructure Co-Doped Ceria: As Electrolytes for IT-SOFC

Abstract

The work provides key insight of extrinsic and intrinsic oxygen vacancies clustering, dissociation mechanism and their influence on oxy-ion conductivity in co-doped ceria system. For present attempt, we develop aliovalent co-doped ceria system Ce 0.85 Ca 0.15/2 M 0.15/2 O 2-δ (M = Sm, Gd, Nd Dy and Sr) with optimize compositions as electrolytes for IT-SOFCs. Structure of all samples are confirmed by X-ray diffraction (XRD) and analyzed by Rietveld refinement using Full-Prof suite. Oxygen vacancies clustering are observed by X-ray absorption techniques (EXAFS & XANES) and Raman spectroscopy. Two separate Raman mode related to extrinsic and intrinsic oxygen vacancies defect spaces are detected; dissociation of oxygen vacancies from the defect clustering are realized from systematic decrease in intensity of the respective Raman mode with temperature. The EXAFS study demonstrates reduction in coordination number with enhancement in interatomic spacing, and disorder factor with increasing temperature. The results are evidenced for oxygen vacancies dissociation from cluster. XANES study reveals co-dopants in ceria causes: (i) suppression of reducing ability of Ce 4+ to Ce 3+ and (ii) asymmetric distribution of Ce-O in CeO 8 polyhedron. Oxy-ion conductivity of co-doped ceria systems are determined by using complex impedance spectroscopy. Co-dopant induced atomic-scale restructuring and oxygen vacancies dissociations are found strongly influence on conduction mechanism.

High Performance Low-Temperature Solid Oxide Fuel Cells Based on Nanostructured Ceria-Based Electrolyte

“…However, pure CeO 2 has poor thermal stability and can be easily sintered at high temperature, which causes a rapid decrease in its oxygen storage/release capacity and catalytic activity [7,8]. In addition, pure CeO 2 itself is an insulator, its ionic conductivity is very low (10 −5 S•cm −1 ) [9]. One approach to overcome this limitation is to use the doping with lower valence metal cations, especially for some trivalent rare earth (RE) cations.…”

In Situ Raman Characterization of SOFC Materials in Operational Conditions: A Doped Ceria Study

“…The higher relative intensity observed for Pr and Tb of the ~570 cm −1 shoulder is ascribed to the higher optical adsorption for these colored compounds [ 20 ]. The vibrational mode at around 600 cm −1 is attributed to oxygen vacancies’ defects (both intrinsic and extrinsic) induced by doping with Ln 3+ [ 21 , 22 ]. Therefore, the band at 600 cm −1 is a consequence of either an ordering effect in the oxygen vacancies to produce confinement of the phonons within an inhomogeneous distribution of domains or structural distortions of the O sublattice.…”

“…Finally, regarding the third effect related to the oxygen vacancies, it is well known that the introduction of Ln 3+ ions causes the F 2g peak to become asymmetric and the appearance of a weak shoulder on the high frequency side that evolves into the observed broad peak at ~570 cm −1 (see Figure 2 ). This weak shoulder is associated with defect species with Oh symmetry, more specifically the existence of complexes in the ceria lattice [ 20 , 22 , 27 ]. In contrast, in the Pr and Tb doped samples the F 2g lines remains symmetric and although there is also a broad peak near 570 cm −1 , this is relatively higher in intensity and narrower than the corresponding in the other Ln doped samples.…”

“…While the changes on Raman shift and FWHM can be related to the aforementioned changes in the cell volume and lifetime of the phonons, the decrease in intensity with the temperature can be assigned to dissociation of oxygen vacancies from defect cluster. The isolation of defects leads to a decrease in intensity [ 22 ].…”

Doping-Induced Combined Fano and Phonon Confinement Effect in La-Doped CeO2: Raman Spectroscopy Analysis

“…17 In a report by Li et al, the importance of MO 8 -type complex species in Zr-doped CeO 2 and the signature of oxygen vacancies for other RE = La, Pr, Sm, Gd, Y, and Lu elements as a dopant were discussed. 10 In addition, Shirbhate et al have investigated the features of extrinsic and intrinsic oxygen vacancies and their clustering in codoped pairs of Ca with Sm, Gd, Nd, Dy, and Sr. 18 All these studies suggest that the doping at the Ce site in CeO 2 results in oxygen vacancies; furthermore, cationic defects also lead to new bands in Raman spectra.…”