Oxygen Transport and Electrochemical Activity of La2NiO4-Based Cathode Materials

Abstract

Mixed-conducting La2Ni1-xMxO4+δ (M = Co, Cu; x = 0 - 0.20) with K2NiF4-type structure possesses significant p-type electronic conductivity and oxygen permeability in combination with relatively low thermal expansion coefficients, (12.5-13.5)×10-6 K-1, which are compatible with that of La(Sr)Ga(Mg)O3-δ (LSGM) solid electrolytes. These phases are of interest as potential cathode materials for intermediate-temperature solid oxide fuel cells (SOFCs). Incorporating copper into the nickel sublattice was found to decrease the sintering temperature needed to achieve sufficient mechanical strength of highly porous electrode layers. As for other nickelates, oxygen permeation through La2Ni1-xMxO4+δ ceramics is limited by both bulk ionic conductivity and oxygen surface exchange. The results on overpotential-current dependencies of La2Ni0.8Cu0.2O4+δ electrodes in contact with LSGM suggest that the electrochemical reaction is essentially localized on triple-phase boundary and/or cathode surfaces. This leads to a moderate performance of La2NiO4+δ-based cathodes at 873-1073K, similar to that of perovskite-type electrode materials, such as La(Sr)Fe(Co)O3-δ and LaFe(Ni)O3-δ, despite higher ionic conductivity of nickelates.