Comprehensive study of functional properties and electrochemical performance of layered lanthanum nickelate substituted with rare-earth elements

The present work is devoted to the comparative study of the absolute oxygen content, thermal expansion, electrical conductivity, and electrochemical performance of the La1.6Ln0.4NiO4+δ (Ln = La, Pr, Nd, Sm, Eu) complex oxides. The thermal expansion coefficients, obtained for the La1.6Ln0.4NiO4+δ compact samples, have approved thermomechanical compatibility of the materials with the Sm0.2Ce0.8O1.9 electrolyte. The highest conductivity value is found to be 107 S cm−1 at 420 °C for the La1.6Sm0.4NiO4+δ sample. The results of scanning electron microscopy, performed after the cycle of measurements on two-layer electrodes with the La1.6Ln0.4NiO4+δ functional layers and the LaNi0.6Fe0.4O3−δ (LNF) collector layers, have demonstrated the stability of the electrode structure under the measurement conditions and the maintenance of high average porosity for both layers. The minimum polarization resistance value, equal to 0.64 Ω cm2 at 700 °C, has been measured for the La1.6Eu0.4NiO4+δ electrode sintered at 1200 °C. Comprehensive distribution function of relaxation times (DFRT or DRT) analyses of the impedance data has been performed to establish the rate-limiting stages of the electrode reaction. Oxygen kinetic parameters calculated in the framework of the Adler-Lane-Steele (ALS) model with considering the microstructural parameters are shown to correlate well with those obtained from the isotope exchange data.