Phase evolution and reactivity of Pr2NiO4+d and Ce0.9Gd0.1O2-d solid oxide cell electrodes
File(s)
Author(s)
Tsai, Chen-Yu
Type
Thesis
Abstract
Pr2NiO4+δ has been reported to possess a better solid oxide cell air electrode performance than the conventional La0.6Sr0.4Fe0.8Co0.2O3-δ air electrode. However, Pr2NiO4+δ is not stable and can decompose and even react with the Ce0.9Gd0.1O2-δ interface layer, located between Pr2NiO4+δ and the zirconia based electrolyte, but the detailed mechanism is unclear. This research has identified the phase evolution of Pr2NiO4+δ and Ce0.9Gd0.1O2-δ under solid oxide air electrode sintering and operating temperatures in air. For example, praseodymium was observed to diffuse from Pr2NiO4+δ to Ce0.9Gd0.1O2-δ to form Ce1-x-yGdxPryO2-δ at 1100°C, leaving NiO as a secondary phase. The praseodymium content of Ce1-x-yGdxPryO2-δ depended on the distance of the initial Ce0.9Gd0.1O2-δ from the interface between Pr2NiO4+δ and Ce0.9Gd0.1O2-δ. The closer it was, the more praseodymium was incorporated. On the other hand, the unreacted Pr2NiO4+δ decomposed to Pr4Ni3O10-δ and Pr6O11 at 800°C in air.
As the aim of the research was to develop an air electrode material which has a reasonable and stable performance operating in the intermediate temperature range of 500-800°C, the resulting products from the previous reactions were chosen, especially Pr4Ni3O10-δ and Ce0.75Gd0.10Pr0.15O2-δ, to form a composite air electrode. The synthesis kinetics, the crystal structure, the oxygen content and the electrical conductivity were first investigated for the Pr4Ni3O10-δ phase. A 50:50 wt.%
Pr4Ni3O10-δ and Ce0.75Gd0.10Pr0.15O2-δ composite was demonstrated to provide the best air electrode performance in comparison with all other compositions. Its area specific resistance was even lower than 0.15 Ωcm2 at temperatures greater than 711°C in air. Indeed, the 50:50 wt.% of Pr4Ni3O10-δ-Ce0.75Gd0.10Pr0.15O2-δ composite electrode showed a stable electrode performance in a long term (7 days) test without any apparent degradation. Therefore, Pr4Ni3O10-δ-Ce0.75Gd0.10Pr0.15O2-δ composites are promising air electrode materials which seem to inherit the electrocatalytic activity of Pr2NiO4+δ but are thermodynamically more stable.
As the aim of the research was to develop an air electrode material which has a reasonable and stable performance operating in the intermediate temperature range of 500-800°C, the resulting products from the previous reactions were chosen, especially Pr4Ni3O10-δ and Ce0.75Gd0.10Pr0.15O2-δ, to form a composite air electrode. The synthesis kinetics, the crystal structure, the oxygen content and the electrical conductivity were first investigated for the Pr4Ni3O10-δ phase. A 50:50 wt.%
Pr4Ni3O10-δ and Ce0.75Gd0.10Pr0.15O2-δ composite was demonstrated to provide the best air electrode performance in comparison with all other compositions. Its area specific resistance was even lower than 0.15 Ωcm2 at temperatures greater than 711°C in air. Indeed, the 50:50 wt.% of Pr4Ni3O10-δ-Ce0.75Gd0.10Pr0.15O2-δ composite electrode showed a stable electrode performance in a long term (7 days) test without any apparent degradation. Therefore, Pr4Ni3O10-δ-Ce0.75Gd0.10Pr0.15O2-δ composites are promising air electrode materials which seem to inherit the electrocatalytic activity of Pr2NiO4+δ but are thermodynamically more stable.
Version
Open Access
Date Issued
2020-07
Date Awarded
2020-11
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Skinner, Stephen
Aguadero, Ainara
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)