Sol-Gel Pechini synthesis of SOFC nanostructured materials (Abstract/Poster in convegno)

Type
Label
  • Sol-Gel Pechini synthesis of SOFC nanostructured materials (Abstract/Poster in convegno) (literal)
Anno
  • 2012-01-01T00:00:00+01:00 (literal)
Alternative label
  • Fasolin Stefano, S. Boldrini, C. Mortalò, F. Agresti, M. Fabrizio, S. Barison (2012)
    Sol-Gel Pechini synthesis of SOFC nanostructured materials
    in School on "Synthesis and Characterization of Novel Nano-Sized Inorganic Materials", Bari, June 17-22, 2012
    (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
  • Fasolin Stefano, S. Boldrini, C. Mortalò, F. Agresti, M. Fabrizio, S. Barison (literal)
Note
  • Poster (literal)
Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
  • CNR-IENI Corso Stati Uniti 4, 35127 PADOVA (Italy) (literal)
Titolo
  • Sol-Gel Pechini synthesis of SOFC nanostructured materials (literal)
Abstract
  • Introduction In last years, new energy devices working with renewable sources were taken into account in order to give different choice to fossil fuel-based systems. Solid Oxide Fuel Cells (SOFCs) are electrochemical systems which produce energy by exploiting the ionic conduction of some materials; their efficiency can reach about 80% by co-generation systems. The fuel can be H2 or hydrocarbons that can give hydrogen by internal reforming. Depending on the type of electrolytic material, SOFCs can be protonic or anionic. Tipically SOFC materials are mixed oxides and their synthesis plays a decisive role in cell performances. For this reason, high purity and dense materials have to be obtained. Sol-Gel Pechini (SGP) method yielded powders with nano-crystalline structure and allow to reach high purity products[1][2][3]. However, this technique requires time-prolonged high temperature treatments in order to eliminate all the organic compounds; as a consequence, the polymeric complex methods are considered time-wasting and energy-expensive. The application of microwaves in synthetic chemistry has worldwide gained acceptance as a promising cost effec-tive method for heating and sintering a variety of materials, as it offers specific advantages in term of speed, energy efficiency, process simplicity, finer microstructures, and lower environmental hazards compared to conventional heat-ing methods[4][5][6]. For this reasons, a Microwave Assisted Sol-Gel Pechini (MWA-SGP) method was set-up in this work for the synthesis of nanostructured oxides for protonic or anionic electrolyte materials for SOFCs.. In this work, examples of SGP and MWA-SGP syntheses are showed for BaCeO3 and LaGaO3 based materials. Experimental With the aim of obtaining high purity and nanostructured BaCe0.65Zr0.20Y0.15O3-? (BCZY) and La0.80Sr0.20Ga0.83Mg0.17O3-? (LSGM), SGP synthesis were carried out. The starting materials for BCZY synthesis were Ba(NO3)2 (Sigma-Aldrich, 99+%), Ce(NH4)2(NO3)6 (Alfa Aesar, 99.5%), ZrO(NO3)2o2.35 H2O (Alfa Aesar, 99.9%), Y(NO3)3o6H2O (Alfa Aesar, 99.9%) as metal precursors and EDTA (ethylenediaminetetraacetic acid, Sigma-Aldrich, 99+%) and ethylene glycol (EG, Aldrich, 99+%) as complexing and polymerizing agents, respectively. The water content of zirconium salt was determined by thermogravimetric analysis. Ammonium hydroxide (Riedel de Haën, NH3 33%) was added to promote the dissolution of EDTA in deionized water (Millipore, Billerica MA, USA). A 10 mol% barium excess was introduced in all of the compositions in order to avoid a barium substoichiometry due to BaO evaporation. The weighed amount of barium nitrate was firstly dissolved in de-ionized water at 80°C. Hence, an aqueous solution of EDTA and ammonia (pH = 9-10) was added dropwise to the barium solution (solution A). In a separate beaker the stoichiometric amounts of cerium, zirconium and yttrium nitrate salts were dissolved in deionized water (solution B). The solution B was then added dropwise to the solution A to avoid irreversible precipitation (figure 1). For LSGM the starting materials were La2O3 (Alfa Aesar, 99.9%), SrCO3 (Alfa Aesar, 99+%), MgO (Alfa Aesar, 99+%), Ga2O3 (Alfa Aesar, 99.9%) as metal precursors and citric acid (Sigma-Aldrich, 99.5 %) and ethylene glycol (EG, Aldrich, 99+%) as complexing and polymerizing agents, respectively. The preparation of nitrate solution and the addi-tion of citric acid and ethylene glycol were carried out as reported by Zhai et al. [7]. The condensation reaction and then the gel formation were carried out, for both BCZY and LSGM, by heating the solution between 50°C and 110°C for 144 h in a hot plate. Upon evaporation of solvent, a viscous, white gel was ob-tained, that gradually became a brown porous solid. The dried gel was pyrolised at 300°C and then treated at 550°C in air for 3 h. The as obtained BCZY precursor powders were calcined in air at 1150°C for 6 h while LSGM precursor powders were calcined in air at 1300°C for 6 h. Figure 1: MWA-SGP method for BCZY. In order to improve purity and nanostructure for both materials, also MWA-SGP were carried out. The difference between SGP and MWA-SGP lies in the use of microwave oven for heating solution and promove condesation and pyrolisis. After microwave heating, starting from low power values (150W) and finishing with higher power (700W) in order to remove most of organic compounds, the BCZY and LSGM precursor powders were calcined as for SGP meth-od. By uniassial pressing of calcined powders, BCZY and LSGM pellets were obtained and subsequently sinterization process were carried out at 1400°C for 10 h and 1450°C for 10 h respectively. BCZY and LSGM powders and pellets were characterized by means of X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analyses. Results and Discussion The Pechini process, where metal ions in a solution are chelated to form metal complexes and then polymerized to form a gel, offers several advantages for processing ceramic powders such as direct and precise control of stoichiome-try, uniform mixing of multi-components on a molecular scale and homogeneity. However, the drawback of this method is the need of prolonged and energy wasting thermal treatments for the effective removal of the large amount of organic precursors. On the other hand, the microwave-induced processing has recently been applied to many systems in order to im-prove the final products and/or to quicken the synthesis procedures. Conversely to the traditional heating mechanism, where the heat radiation occur from exterior to interior, the microwave heating, which supply volumetric heat conduc-tion, can provide a higher heating rate and a more homogeneous heating without thermal gradients. For both BCZY and LSGM materials, SEM and XRD characterizations allowed to demonstrate that single-phase nanostructured powders were obtained for both materials. Moreover, the microwave heating induced a higher phase puritiy and allowed to obtain denser pellets, besides the reduction in heating time. Furthermore, some preliminary con-ductivity tests confirmed the high potential of MWA-SGP synthesis on obtaining functional materials. Conclusions SGP and MWA-SGP methods have been exploited to prepare BCZY and LSGM solid solution powders. Fine, ho-mogeneous and single phase powders were obtained in both cases by using MWA-SGP. Pellets were succefully sintered and high relative density values (around 97% in both cases) were achieved. References 1. S. Barison, M. Battagliarin, T. Cavallin, S. Daolio, L. Doubova, M. Fabrizio, C. Mortalò, S. Boldrini, R. Gerbasi, Fuel Cells 5 (2008) 360. 2. S. Barison, M. Battagliarin, T. Cavallin, S. Daolio, L. Doubova, M. Fabrizio, C. Mortalò, S. Boldrini, L. Malavasi, R. Gerbasi, J. Mater. Chem. 18 (2008) 5120. 3. G. Chiodelli, L. Malavasi, C. Tealdi, S. Barison, M. Battagliarin, L. Doubova, M. Fabrizio, C. Mortalò, R. Gerbasi, J. All. Compd. 470 (2009) 477. 4. M. Nüchter, B. Ondruschka, W. Bonrath, A. Gum, Green Chem. 6 (2004) 128. 5. Z. Xie, J. Yang, X. Huang, Y. Huang, J. Eur. Ceram. Soc. 19 (1999) 381. 6. S. Liu, X. Qian, J. Xiao, J. Sol-Gel Sci. Technol. 44 (2007), 187. 7. Y. Zhai, C. Ye, J. Xiao, L. Dai, Journal of Power Sources, 163 (2006) 316. (literal)
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