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Synthesis and Characterization of Praseodymium Nickelate for Low Temperature Solid Oxide Fuel Cell Cathode

Naeini, Mina | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50338 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Faghihi Sani, Mohammad Ali
  7. Abstract:
  8. Solid oxide fuel cells as high temperature electrochemical devices draw much attention in the last decades due to their fuel flexibility, high efficiency and low pollution. However, lowering operating temperature from about 850°C to around 650°C without significant overpotential loss, in order to lower costs and increase cells life time has remained a challenge. Recently, a new family of mixed ionic and electronic conducting ceramics (MIECs) which are formulated Ln2NiO4+δ (Ln= La,Nd,Pr) and crystallized in Ruddlesden–Popper structure, have been regarded as appropriate cathode materials for the low or intermediate temperature solid oxide fuel cells (IT-SOFC). Amongst these compounds, Pr2NiO4+δ has the best electrochemical properties. In the present study, Pr2NiO4+δ was synthesized via a combustion sol-gel method similar to that outlined by Pechini. As the presence of a small amount of a secondary phase affects cathode properties, the influence of calcination temperature on the purification of the samples was studied, and XRD results showed that pure single phase Pr2NiO4+δ was obtained after calcination at 1200°C. In order to investigate the effect of fuel nature and content on oxygen non-stoichoimetry level (δ), either urea or citric acid with different fuel/nitrate rations was used in synthesis process. Regarding to iodometric titration results, increasing fuel/nitrate ratio enhances δ value and samples synthesized with urea has higher δ levels. For example, increasing citric acid/nitrate ratio from 1 to 3 resulted in δ increment from 0.12 to 0.18 and enhancing urea/nitrate ratio from 1 to 3 led to δ enhancement from 0.15 to 0.22. Four-point probe electrical conductivity measurements indicated that samples with higher δ values show higher electrical conductivities, however δ increment results in less thermal stability. Therefore Pr2NiO4.22 is the most non-stoichiometric compound with the highest electrical conductivity, which is thermally stable under IT-SOFCs operating condition
  9. Keywords:
  10. Cathodes ; Solid Oxide Fuel Cell (SOFC) ; Sol-Gel Autocombustion Method ; Stoichiometry ; Praseodymium Nickelate ; Over-Stoichiometry Oxygen ; Fuel to Nitrate Ratio

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