Impact of Oxygen Deficiency on the Electrochemical Performance of K2NiF4-Type (La1-xSrx)2NiO4-[delta] Oxygen Electrodes

• Published in: ChemSusChem 2017-02, Vol.10 (3), p.600
• Main Authors: Kravchenko, Ekaterina, Zakharchuk, Kiryl, Viskup, Alexander, Grins, Jekabs, Svensson, Gunnar, Pankov, Vladimir, Yaremchenko, Aleksey
• Format: Article
• Language: English
• Subjects: Electrodes; Electrolytes; Oxygen
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201601340

Perovskite-related (La1-xSrx)2NiO4-[delta] (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. (La1-xSrx)2NiO4-[delta] 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 [delta]=0.40 for x=0.8 at 950°C in air. The electrical conductivity of (La1-xSrx)2NiO4-[delta] ceramics at 500-1000°C and p(O2)≥10-3atm is p-type metallic-like. The highest conductivity, 300Scm-1 at 800°C in air, is observed for x=0.6. The average thermal expansion coefficients, (14.0-15.4)×10-6K-1 at 25-900°C in air, are sufficiently low to ensure the thermomechanical compatibility with common solid electrolytes. The polarization resistance of porous (La1-xSrx)2NiO4-[delta] electrodes applied on a Ce0.9Gd0.1O2-[delta] 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.