Redox stability of Sc-doped La0.6Sr0.4FeO3-δ for tubular solid oxide cells interconnector

Ceramic interconnectors of tubular solid oxide cells should require fundamental properties as follow, because they are facing on both a reducing and oxidizing atmosphere at anodes and cathodes. Firstly, they should separate... [ view full abstract ]

Ceramic interconnectors of tubular solid oxide cells should require fundamental properties as follow, because they are facing on both a reducing and oxidizing atmosphere at anodes and cathodes. Firstly, they should separate different gas atmospheres of an anode (inside) and a cathode (outside) by a dense layer with high chemical and redox stability, because the ceramic interconnectors are placed on between an anode of one individual cell to the cathode of the neighboring cell in a stack. Secondly, pure and high electronic conduction are one of the key properties to get a high performance by minimizing ohmic loss of the multi-layer stacking structure. With the objective of introducing a redox stable ceramic interconnector, the optimum concentration in La_0.6Sr_0.4Fe_1-xSc_xO_3-δ (LSFSc) has been determined by analyzing the variation of composition, pH, synthetic temperature and heat treatment time. 

The synthesis of La_0.6Sr_0.4Fe_1-xSc_xO_3-δ (x=0.01, 0.05, 0.1, 0.2 and 0.3) powders follow a Pechini type polymerizerlable complex method. The effect of solution pH on the crystalline phase and stability of LSFSc was evaluated by adjusting the pH of the solution from pH 2 to pH 9 with ammonia water. The powder were calcinated at 900 and 1200 °C for 2, 6, and 24 h to eliminate the organic residual and to investigate the effect of the heat-treatment on the redox stability of the LSFSc crystalline phase.

The crystalline phases of LSFSc are stable when the solution pH is low (pH=2), and the calcination temperature is sufficiently high (T≥1200°C). From the XPS analysis, it is recognized that the incorporation of Sc in the LSF lattice makes its structural stability even more stable under the reduction condition. The phase stability of La_0.6Sr_0.4Fe_1-xSc_xO_3-δ was obtained when the Sc concentration was over 10 mol%. Therefore, as depicted in figure below, La_0.6Sr_0.4Fe_0.9Sc_0.1O_3-δ is considered to be the most stable composition for a redox stable and electrically conductive ceramic interconnector for tubular solid oxide cells.