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

The submicron powder of La2Ni0.8Cu0.2O4+delta 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)(0.98)Ga0.8Mg0.2O3-delta (LSGM) solid electrolyte. In air, dense ceramics of LaNi0.8Cu0.2O4+delta possess thermal expansion coefficient of 13.3 x 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/cm(2). As for the oxygen transport through dense membranes, the results on electrode behavior, including the overpotential-microstructure relationships and the p(O-2) 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+delta cathode, screen-printed onto LSGM and annealed at 1473 K, from 330 down to approximately 175 mV at 50 mA/cm(2). (C) 2003 Elsevier B.V. All rights reserved.