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Electrochemical Properties and Stability of Ruddlesden-Popper (RP) Nickelates as Cathodes for IT-SOFC

Khoshkalam, Mohammad | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53495 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Faghihi Sani, Mohammad Ali; Madaah Hosseini, Hamid Reza
  7. Abstract:
  8. For improving cost competitiveness of both SOEC and SOFC technology, it is desirable to reduce the temperature of operation preferably down towards 500 oC – 600 oC, as this will slow down the rate of various degradation processes and allow use of much cheaper materials for auxiliary components. In this range, the oxygen electrode typically dominates the cell resistance, and hence there is a need to develop cost effective electrodes with improved performance at low temperature. Whereas the oxygen exchange on Ruddlesden-Popper type Ni based compounds like Pr2NiO4 with interstitial oxygen defects is known to be very fast, reported electrode performance of micron-sized composites based on these types of compounds has fallen short of expectations considering the material properties. Here, we report the results on modifying various back-bone type electrodes (Ce0.9Gd0.1O2-based (CGO), La0.6Sr0.4FeO3-based (LSF), La(Ni,Fe)O3/Ce0.9Gd0.1O2 (LNF/CGO), and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2-based (LSCF/CGO)) via infiltration. Nitrate precursors were used for the infiltration targeting several different compositions belonging to the broad class Pr2(Ni1-xCux)O4. Marked performance improvements could hereby be achieved, including a reduction by a factor of 3 of the polarization resistance for both the LSF and LSCF/CGO based state of the art electrodes at 600 oC. In a LNF/CGO composite backbone, infiltration with Pr-nitrate also led to marked electrode performance improvement; reaching 0.14 Ω.cm2 at 550 oC and 0.4 Ω.cm2 at 500 oC. Therefore, at these temperatures the oxygen electrode no longer limits overall cell performance. The origin of the performance improvement is elucidated by comparing the behavior of these nano-structured porous electrodes with simplified model systems such as oxygen exchange investigations on “decorated” surfaces, where nano-particles have been deposited on the surface of a macroscopic bar made out of the electrode material. Comprehensive studies demonstrated that the increase in the surface exchange rate of oxygen at the decorated electrode surfaces is the source of enhanced electrode activity
  9. Keywords:
  10. Solid Oxide Fuel Cell (SOFC) ; Cathodes ; Electrocatalytic Activity ; Oxygen Electrode ; Praseodymium Nickelate ; Ruddlesden-Popper Cathodes ; Infiltration

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