A review of defect structure and chemistry in ceria and its solid solutions

Abstract

Ceria and its solid solutions play a vital role in several industrial processes and devices. These include solar energy-to-fuel conversion, solid oxide fuel and electrolyzer cells, memristors, chemical looping combustion, automotive 3-way catalysts, catalytic surface coatings, supercapacitors and recently, electrostrictive devices. An attractive feature of ceria is the possibility of tuning defect-chemistry to increase the effectiveness of the materials in application areas. Years of study have revealed many features of the long-range, macroscopic characteristics of ceria and its derivatives. In this review we focus on an area of ceria defect chemistry which has received comparatively little attention -defect-induced local distortions and short-range associates. These features are non-periodic in nature and hence not readily detected by conventional X-ray powder diffraction. We compile the relevant literature data obtained by thermodynamic analysis, Raman spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Each of these techniques provides insight into material behavior without reliance on longrange periodic symmetry. From thermodynamic analyses, association of defects is inferred. From XAFS, an element-specific probe, local structure around selected atomic species is obtained, whereas from Raman spectroscopy, local symmetry breaking and vibrational changes in bonding patterns is detected.We note that, for undoped ceria and its solid solutions, the relationship between short range order and cation-oxygen-vacancy coordination remains a subject of active debate. Beyond collating the sometimes contradictory data in the literature, we strengthen this review by reporting new spectroscopy results and analysis. We contribute to this debate by introducing additional data and analysis, with the expectation that increasing our fundamental understanding of this relationship will lead to an ability to predict and tailor the defect-chemistry of ceria-based materials for practical applications. monoxide, and NO x from the exhaust stream, precise control of the oxygen-to-fuel ratio is necessary. Ceria has the capacity to serve as an oxygen buffer by actively varying its oxygen nonstoichiometry, supplying oxygen when required for carbon oxidation, and removing it as necessary for NO x reduction. Another promising use of the oxygen storage capacity of ceria is in solar-driven thermochemical water splitting. 15,16 During this cyclic process, ceria releases oxygen at extremely high temperatures (typ. 1500 1C), which can be achieved by solar concentration. Subsequently, the material is cooled to 800-1000 1C, and the oxygen vacancies generated from the prior reduction step are filled with oxygen through a water and CO 2 splitting reaction. Though not treated in this review, it is noteworthy that doping with tetravalent cations, Zr 4+ or Hf 4+ , increases the ease by which the reduction of the host material occurs. 17,18 This behavior is used to increase the oxygen storage capacity in exhaust catalysts, or to decrea...

Visible Emission on Nanostructured CeO2 Thin Films Obtained by Spray Pyrolysis

“…34‐0394) with a fluorite structure (space group Fm3m ). [ 1,2,41,42 ] Secondary phases are not detected and the structure does not change with the thermal annealing. The calculated lattice parameter is a = (0.5406 ± 0.0004) nm and a = (0.5424 ± 0.0007) nm for as‐grown and thermal treated samples, respectively.…”

“…Cerium dioxide (CeO 2 ) is a multifunctional material with several areas of applications, related to properties such as good lattice matching with silicon (0.35%), a bandgap of around 3.3 eV, a high dielectric constant ( ε ≈ 26), high ionic conductivity, and high temperature stability. [ 1–4 ] The optical and electrical properties allow its use in silicon‐on‐insulator structures, stable capacitor devices for large‐scale integration, solar cells, protective coatings, and biological, biomedical, and pharmaceutical applications. [ 4–7 ] The high ionic conductivity and thermal stability have attracted great interest for applications such as gas sensors, solid state energy conversion membranes, and electrolyte or anode materials for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs).…”

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

“…The chemical capacitance of an oxide is a measure for how much the oxygen nonstoichiometry δ depends on the oxygen partial pressure (or overpotential), which is quantified by Equation 16. For GDC, nonstoichiometry data is available from many well-agreeing sources in the literature, e.g., [15,[49][50][51]63]. Therefore, the expected chemical capacitance can be reliably predicted from literature data, as shown in Figure 10a.…”

“…Ceria-based anodes are a key component with remarkably low polarization resistance, which enables high power density at intermediate temperatures of 600-700 • C. This low area-specific polarization resistance (ASR) is likely caused by the high ionic conductivity and mixed ion/electron conduction of acceptor doped ceria, which was already broadly investigated in literature [14][15][16] and the high activity of ceria for catalyzing redox reactions [17,18]. For further optimization, detailed insight into the reaction mechanisms on such electrodes is of technological and scientific interest.…”

Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2materials

“…8 Beyond heterogeneous catalysis, biomedical applications of ceria are being explored, 9 and the material also finds use in UV-shielding, 10 as an abrasive agent, 11 and in humidity sensors. 12 The defect chemistry of ceria is crucial in determining its properties, 13 as is its crystallite morphology and size, 14 particularly on the nanoscale. 15 These aspects of fine control of properties of ceria mean that the synthesis method used is of the utmost importance in forming materials with desirable properties.…”