Impact of Oxygen Deficiency on the Electrochemical Performance of K₂NiF₄-Type (La_1−xSr_x)₂NiO_4−δ Oxygen Electrodes

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• 作者：Ekaterina Kravchenko ; Kiryl Zakharchuk ; Alexander Viskup ; Dr. Jekabs Grins ; Prof. Gunnar Svensson ; Prof. Vladimir Pankov and Dr. Aleksey Yaremchenko
• 刊名：ChemSusChem
• 出版年：2017
• 出版时间：February 8, 2017
• 年：2017
• 卷：10
• 期：3
• 页码：600-611
• 全文大小：2503K
• ISSN：1864-564X

文摘

Perovskite-related (La_1−xSr_x)₂NiO_4−δ (x=0.5–0.8) phases were explored for possible use as oxygen electrodes in solid electrolyte cells with a main focus on the effect of oxygen deficiency on the electrocatalytic activity. (La_1−xSr_x)₂NiO_4−δ solid solutions were demonstrated to preserve the K₂NiF₄-type tetragonal structure under oxidizing conditions. Acceptor-type substitution by Sr is compensated by the formation of oxygen vacancies and electron holes and progressively increases high-temperature oxygen nonstoichiometry, which reaches as high as δ=0.40 for x=0.8 at 950 °C in air. The electrical conductivity of (La_1−xSr_x)₂NiO_4−δ ceramics at 500–1000 °C and p(O₂)≥10⁻³ atm is p-type metallic-like. The highest conductivity, 300 S cm⁻¹ at 800 °C in air, is observed for x=0.6. The average thermal expansion coefficients, (14.0–15.4)×10⁻⁶ K⁻¹ at 25–900 °C in air, are sufficiently low to ensure the thermomechanical compatibility with common solid electrolytes. The polarization resistance of porous (La_1−xSr_x)₂NiO_4−δ electrodes applied on a Ce_0.9Gd_0.1O_2−δ solid electrolyte decreases with increasing Sr concentration in correlation with the concentration of oxygen vacancies in the nickelate lattice and the anticipated level of mixed ionic–electronic conduction. However, this is accompanied by increasing reactivity between the cell components and necessitates the microstructural optimization of the electrode materials to reduce the electrode fabrication temperature.