Preparation and performance of Na-doped La2Ce2O7 electrolytes for protonic ceramic fuel cells

The protonic material La2Ce2O7 exhibits good tolerance to H2O and CO2 compared to BaCeO3-based materials and has become increasingly popular for operation at low-to-intermediate temperatures in protonic ceramic fuel cells. In this work, doping La2Ce2O7 with Na in a series with varying compositions is studied. All of the precursors are prepared by a common citrate-nitrate combustion method. X-ray diffraction images reveal that all of the La2-xNaxCe2O7-δ samples have a cubic structure. The La2-xNaxCe2O7-δ pellets are characterized by scanning electron microscopy and are observed to be dense without holes. The effects of Na-doping on the La2Ce2O7 electrical conductivity are carefully investigated in air at 350-800 °C and 5%H2-95% Ar environments at 350-700 °C. It is found that different levels of Na doping in La2Ce2O7 are conducive to improving the electrical conductivity and sinterability. Among the pellets, La1.85Na0.15Ce2O7-δ exhibited the highest electrical conductivity in air and 5% H2-95% Ar atmospheres. Anode-supported half cells with La1.85Na0.15Ce2O7-δ electrolyte are also fabricated via a dry-pressing process, and the corresponding single cell exhibited a desirable power performance of 501 mW cm−2 at 700 °C. The results demonstrate that La1.85Na0.15Ce2O7-δ is a promising proton electrolyte with high conductivity and sufficient sinterability for use in protonic ceramic fuel cells operating at reduced temperatures.