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Chun-Hua Yan

Controllable Synthesis and Properties of Ceria- and Zirconia- Based Functional Materials. Chun-Hua Yan. R are E arth S eparation & I norganic M aterials ( R E S I M , 睿新室 ) State Key Lab of Rare Earth Mater. Chem. & Appl., PKU-HKU Joint Lab on Rare Earth Mater. & Bioinorg. Chem.

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Chun-Hua Yan

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  1. Controllable Synthesis and Properties of Ceria- and Zirconia- Based Functional Materials Chun-Hua Yan Rare Earth Separation & Inorganic Materials (RESIM, 睿新室) State Key Lab of Rare Earth Mater. Chem. & Appl., PKU-HKU Joint Lab on Rare Earth Mater. & Bioinorg. Chem. Peking University, Beijing 100871, China yan@pku.edu.cn

  2. Outline • System I : Ceria • System II : Zirconia • System III : Ceria-zirconia • Conclusions

  3. Coordination Chemistry Solid State Chemistry Nanocrystals Functional Materials Controllable synthesis & assembly Properties

  4. System I : CeO2  Ce3+/Ce4+ transfer  Fluorite cubic structure  Large bandgap energy (3.2 eV)  High refractive index (2.1)  Good anti-wear ability • Catalyst • Ionic conductor • UV-blocking reagent • Optical materials • Polishing materials

  5. Precipitation Sonochemistry Pickering, et. al.J. Eur. Ceram.Soc. 1999, 19, 1925. Yu, et. al.J. Colloid Inter. Sci. 2003, 260, 240. Microwave Aerosol decomposition Yang, et. al.Mater. Lett. 2003, 57, 1880. Okuyama, et. al.J. Mater. Chem. 2001, 11, 2925.

  6. Motivation: Inorganic Chemistry Organometallic Chemistry Material Science Nanocrystals Polymer Science Self-assembly Behavior ? Surface Structure CeO2

  7. Ce3+ + xOH + yC2H5OH[Ce(OH)x(C2H5OH)y]3x [Ce(OH)x(C2H5OH)y]3x+ 1/4O2 + 1/2H2O[Ce(OH)m(C2H5OH)n]4m [Ce(OH)m(C2H5OH)n]4m+ H2O + OH- CeO2mH2OnC2H5OH CeO2mH2OnC2H5OHCeO2+mH2O+nC2H5OH KOH + C2H5OH KOC2H5 + H2O Size-Controllable Ceria Nanocrystals CeO22.6 nm CeO26.9 nm

  8. Bandgap Energy UV-Vis Spectra Bandgap Energy vs Size • Quantum Confinement Effect  Blueshift • Dielectric Confinement Effect  Redshift Yan, et. al.J. Phys. Chem. B 2003, 107, 10159.

  9. Water-Soluble Ceria Nanocrystals PVP No PVP 180C RT

  10. Self-Organized Superstructure Polymer Con. & Base type Isolated Short chain Unpublished results Pearl necklace Dendritic

  11. Thermolysis Method Precursor Surfactant Precursor Cerium benzoylacetonate Ce(BA)4 Surfactant Oleylamine (OM) Injection Non-injection Product Polar solvents Non-polar solvents Precipitate Colloid

  12. Monodispersed Ceria Nanocrystals CeO2 nanopolyhedron UV-Vis spectra 2.63  0.24 nm (S.D. = 9 %) Blue-shifted absorption Yan, et. al.Angew. Chem. Int. Ed. 2005, 44, 3256.

  13. Ceria Nanostructures (NH4)2Ce(NO3)6+4ROH+6NaOCH3Ce(OR)4+6NaNO3+2NH3+6CH3OH Ce(OR)4CeO2+2ROR Thermolysis Ce(OR)4+4H2OCe(OH)4+4ROH Hydrolysis Ce(OR)4+2HOCH2CH2OHCe(OCH2CH2O)2+4ROH Alcoholysis Long-range ordered mesostructure Monodispersed nanocrystals Polycrystalline nanorods Unpublished results

  14. 111 100 111 CeO2 Nanostructures Shape modification via capping effect: CeO2 truncated octahedron cube Increasing the amount of acetate ions

  15. Surface-dependent oxygen storage capacity (OSC) Yan, et. al.J. Phys. Chem. B (in press).

  16. O2 Sensor; SOFCs Catalysis; Optics; Membrane Ceramics; ZTA; TBCs System II : ZrO2 • High ionic conductivity • High mechanic strength • High heat resistance • Good thermal stability • High refractive index (2.2)

  17. Fluorite cubic Tetragonal Monoclinic 1170C 2370C Crystal Structure P42/nmc a = 3.64 Å c = 5.27 Å Z = 2 Dx = 5.861 g cm-3 Fm3m a = 5.09 Å Z = 4 Dx = 6.206 gcm-3 P21/c a = 5.31 Å, b = 5.21 Å, c = 5.15 Å  = 99.2, Z = 4,Dx = 5.82 g cm-3

  18. Stabilization of t or c Phase • Crystallite Size Effect Critical size (Dc) • Stabilizer Effect Aliovalent doping(Ca2+,Mg2+, Y3+, Sc3+, etc.) • Microstrain Effect Preparation method Garvie J. Phys. Chem. 1965, 69, 1238. Djuradao et al.J. Solid State Chem. 2000, 149, 399. Yashima et al.Solid State Ionics 1998, 86 - 88, 1131. Lin and Duh J. Am. Ceram. Soc. 1998, 81, 853.

  19. Sol-gel Preparation Methods ZrO2 9YSZ Coprecipitation Pramanik, et. al.J. Eur. Ceram. Soc. 2000, 20, 1289. Badwal, et. al. Solid State Ionics 1998, 109, 167.

  20. Motivation: Micrometer Nanometer Phase transformation Doping tolerance Surface state ? Electrical, Optical, Mechanical properties

  21. (ZrO2)0.98(RE2O3)0.02 : Synthesis Urea-based hydrolysis + Hydrothermal treatment 2ScSZ 2YSZ Monoclinic content vs T

  22. Phase Transformation : 2ScSZ UV-Raman Vis-Raman Yan, et al.Phys. Chem. Chem. Phys.2003, 5, 4008.

  23. (ZrO2)0.96(RE2O3)0.04 : Synthesis Urea-based hydrolysis + Hydrothermal treatment 4ScSZ 4YSZ

  24. 4ScSZ (400C) 4ScSZ (800C) Texture: Microstrain Microstrain vsT

  25. Phase Transformation & Electronic Property Monoclinic content vs T Crystallite size vs T Yan, et al.J. Am. Ceram Soc. 2004, 87, 2275.

  26. (ZrO2)1-x(Sc2O3)x (x = 0.02-0.16) 8ScSZ (180C) Grain size Tetragonality Microstrain vs Composition 8ScSZ (800C)

  27. Solid Solution Limit Nanometer Micrometer Phase Transformation Yan, et al.Phys. Chem. Chem. Phys. 2004, 6, 5410.

  28. (ZrO2)0.92(RE2O3)0.08 Thin Films Sol-gel + Spin coating + Annealing treatment Conductivity vs T SEM AFM Yan, et al.Appl. Phys. Lett. 2000, 77, 3409. Yan, et al.Chem. Mater. 2001, 13, 372.

  29. (ZrO2)0.92(RE2O3)0.08 Size-Dependent Electrical Conductivity TEM Conductivity vs T Yan, et al. Solid State Ionics, 2004, 166, 391. Yan, et al. J. Mater. Chem. 2002, 12, 970. SEM

  30. System III : CeO2 - ZrO2 Three-Way-Catalysts (TWCs): Pt, Rh, Pd, etc. \ CeO2 - ZrO2 \ -Al2O3 • High activity and selectivity  Fast response • High thermal stability  High OSC value

  31. Crystal Structure Tetragonality Phase diagram

  32. Catalytic Activity vs Composition Experimental: Meeyoo et al.Appl. Catal. A 2002, 234, 221. Cuif et al.SAE 970463 1997. Theoretic: Kaspar et. al.J. Phys. Chem. B 1997, 101, 1750.

  33. Precipitation Mechanical milling Meeyoo et. al.Catal. Today 2001, 68, 53. Trovarelli et. al.J.Catal. 1997, 169, 490. Sol-gel Forced hydrolysis Meeyoo et. al.Catal. Today 2001, 68, 53. Hirano et. al.J. Solid State Chem. 2001, 158, 112.

  34. Motivation: Hydrothermal Synthesis Property Structure OSC XRD, TEM, etc.

  35. Mesoporous Ce0.2Zr0.8O2 Nanocrystals CO(NH2)2+3H2OCO2+2NH4++2OH (1-x)Ce3++xZrO2++yOH-+(1-x)/4O2+zH2O [Ce1-xZrx(OH)y(H2O)z]4y [Ce1-xZrx(OH)y(H2O)z]4y Ce1-xZrxO2 500C 160C Low-angle XRD Higher OSC value! Yan, et. al. Phys. Chem. Chem. Phys. 2004, 6, 1056.

  36. Ceria-Zirconia Solid Solutions Ce1-xZrxO2 (x = 0 – 0.8) XRD Raman spectra • Single phase • High crystallinity • Uniform size • Weak aggregation HRTEM & Size-Distribution

  37. Lattice Strain vs Composition

  38. OSC vs Lattice Strain Substitute Lattice strain Oxygen vacancy Interstitial oxygen defect Yan, et. al. J. Phys. Chem. B 2004, 108, 12481.

  39. XRD XRF Raman OSC BET XAFS Rare Earth Doped Ceria-Zirconia Urea H2O Ce4+ (97 pm) Zr4+ (84 pm) La3+ (116 pm) Pr3+ (113 pm) Nd3+ (111 pm) Y3+ (102 pm) OH- Ce4+, ZrO2+, RE3+ H2O Hydrothermal (T, t) Ce1-x-yZrxREyO2•nH2O 1000 C, 100 h Ce1-x-yZrxREyO2

  40. Samples & Characterizations S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 Surface area  OSC value 

  41. Thermal Stability XRD patterns of S1-3 and S9-11 Comparison between S2and S10 (*: tetragonal) The introduction of RE3+ stabilizes CeO2–ZrO2 solid solutions after calcining at high temperature (1000C) for long time (100 h)

  42. Structural Probe : XAFS Zr-O Zr-M Nagai, et. al.Catal. Today 2002, 74, 225. FT k3 data of Zr-K edge of S2 and S10 The introduction of RE3+ causes the disordering of cation-cation periodicity in CeO2–ZrO2 lattice and stabilizes the oxygen defects, which is different from the references. Unpublished results

  43. Conclusions • Size, shape or surface-tunable CeO2, ZrO2 or CeO2-ZrO2 nanocrystals can be obtained via solution-based soft chemical methods. • These functional materials show structure-dependent optical, electronic, and catalytic properties, which can be enhanced by more robust synthetic routes. • Better-performing ceria and zirconia based functional materials can be designed and obtained by controllable synthesis in solution phase.

  44. Acknowledgements Prof Y. W. Zhang Prof. L. D. Sun Prof. L. P. You Prof. Y. Kou Prof. B. X. Lin Prof. H. C. Liu Dr. G. Xu Dr. Z. G. Yan Mr. R. Si Mr. X. Sun Mr. H. X. Mai MOST NSFC MOE PKU

  45. Thank you for your attention

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