Effect of sintering temperature on NO decomposition by solid electrolyte cells with LSM-SDC composite cathodes

Abstract

A series of solid electrolyte cells with La0.8Sr0.2MnO3 (LSM)-Ce0.8Sm0.2O1.9 (SDC) composite cathodes was fabricated for the electrochemical decomposition of nitric oxide (NO). The LSM and SDC powders were synthesized by a combined EDTA-citrate method. Thermogravimetry with differential scanning calorimetry, X-ray diffraction analysis, scanning and transmission electron microscope with electron diffraction were performed to characterize the synthesized powders. The NO conversions and power consumptions of the solid electrolyte cells with the cathodes sintered at 900–1200 °C were evaluated. The electrochemical properties, microstructures, and crystalline phases of the cathodes were further studied by electrochemical impedance spectrum, scanning electron microscope and X-ray diffraction, respectively. The NO conversions and electrochemical performances of the cells at different operating temperature were also investigated. It was concluded that the LSM and SDC powders calcined at 900 °C both showed good crystal structures with high purity. The cell with the cathode sintered at 1100 °C had the highest NO conversion of 65.4% and the lowest power consumption of 0.2024 W under 80 mA applied current. The total polarization resistances of the cells with the cathodes sintered at 900–1200 °C were 63.32, 41.75, 38.11 and 97.57 Ω cm2 in 800 ppm NO, respectively. The cathode sintered at 900 °C had an incompact structure and connected with the electrolyte loosely, thereby impeding the NO adsorption on the cathode surface and the transfer of O2− from three phase boundary (TPB) to electrolyte. The excess sintering temperature of 1200 °C resulted in a dense structure of cathode and La2Zr2O7 formation at the interface between the cathode and electrolyte, thereby leading to a poor NO decomposition performance. This study also found that the NO conversion increased with the rise of operating temperature and 600 °C was not suitable for operation because of the electrode degradation caused by the overvoltage.