Electrochemical performance of Co-containing mixed oxides as oxygen electrode materials for intermediate-temperature solid oxide electrolysis cells

Composite materials Nd0.8Sr1.2CoO4 − δ - Nd0.5Sr0.5CoO3 − δ were prepared and evaluated as oxygen electrode for intermediate temperature reversible solid oxide cells (IT-RSOCs). Nd0.8Sr1.2CoO4 − δ (NSC0812) material with A2BO4-type structure was prepared by citrate-nitrate combustion method, and Nd1 − xSrxCoO3 − δ (x = 0.3, 0.4, 0.5, 0.6, 0.7) materials with perovskite structure were prepared via the glycine nitrate process (GNP). The crystal structure, thermal expansion, electrical conductivity and electrochemical properties were investigated. The lattice volume of Nd1 − xSrxCoO3 − δ increases with increasing Sr content, x. XRD analysis show that no reaction occurs between oxygen materials and Gd0.2Ce0.8O1.9 (GDC). The thermal expansion coefficient increases with increasing x. AC impedance spectroscopy on symmetric cells was used to assess electrochemical performance of the oxygen electrode materials. Nd0.5Sr0.5CoO3 − δ (NSC0505) has the lowest total cathodic polarization resistance for 0.099 Ω cm2 at 750 °C. The composite materials NSC0505 and NSC0812 with the ratio of 7:3 reveals a better performance than either material individually at 700 °C, which is due to introduce of more oxygen vacancies and oxygen interstitials with NSC0812. For an electrolysis voltage of 1.3 V, current densities in a single cell fabricated with Nd0.5Sr0.5CoO3 − δ - Nd0.8Sr1.2CoO4 − δ are 420 mA cm−2 at 800 °C.