Surface-limited oxygen transport and electrode properties of La2Ni0.8Cu0.2O4+δ

The submicron powder of La2Ni0.8Cu0.2O4+δ with K2NiF4-type structure, having grain size of 30–60 nm, was synthesized via glycine–nitrate process (GNP) and used for the preparation of porous cathode layers applied onto (La0.9Sr0.1)0.98Ga0.8Mg0.2O3−δ (LSGM) solid electrolyte. In air, dense ceramics of La2Ni0.8Cu0.2O4+δ possess thermal expansion coefficient of 13.3×10−6 K−1 at 400–1240 K, p-type electronic conductivity of 50–85 S/cm at 800–1300 K and relatively high oxygen permeability limited by the surface exchange. These properties provide a substantially high performance of porous electrodes, exhibiting cathodic overpotential lower than 50 mV at 1073 K and current density of 200 mA/cm2. As for the oxygen transport through dense membranes, the results on electrode behavior, including the overpotential–microstructure relationships and the p(O2) dependence of polarization resistance, suggest that the cathodic reaction rate is affected by surface-related processes. Due to this, electrode performance can be considerably enhanced by surface activation, particularly via impregnation with Pr-containing solutions, and also by decreasing fabrication temperature. At 873 K, the surface modification with praseodymium oxide decreases overpotential of La2Ni0.8Cu0.2O4+δ cathode, screen-printed onto LSGM and annealed at 1473 K, from 330 down to approximately 175 mV at 50 mA/cm2.