Synthesis and characterization of La2NiO4-d coatings deposited by reactive magnetron sputtering using plasma emission monitoring

Abstract

It is well known that the short life time and the high cost of each component of nowadays Solid Oxide Fuel Cells (SOFC) are induced by their high operating temperature. Many researches focus on the decrease of this operating temperature without reduction of the fuel cell performances (IT-SOFC). Regarding the cathode, one solution is to increase the electrocatalytic properties. Purely electronic conductor perovskite materials (for example LSM: La1-xSrxMnO3) are used in standard SOFC devices. A2MO4+d compounds, with K2NiF4 structure have recently been investigated as substitutes to LSM. Indeed, these materials are mixed ionic and electronic conductors (MIECs) that moreover exhibit rather high electrocatalytic properties. It is then possible to synthesize them as dense materials for SOFC cathodes. Among these materials, lanthanum nickelates La2NiO4+d exhibits convenient electrochemical characteristics. Its thermal expansion coefficient (TEC) is very close to that of the most commonly used electrolyte materials (13 10-6 K-1, 11.9 10-6 K-1 and 11.6 10-6 K-1 for La2NiO4+d, CeO2-Gd2O3 (CGO) and ZrO2-Y2O3 (YSZ) respectively). Its oxygen ionic conductivity and surface exchange coefficient are interesting and seem much better than those of La1-xSrxMnO3 (LSM) and La1-xSrxCo1-yFeyO3 (LSCF), the most commonly used cathodes.

The deposition of La2NiO4 coatings by reactive magnetron sputtering has already successfully been performed under so called stable conditions in a laboratory vessel. In this study, we investigate the feasibility of La2NiO4+d coatings deposited by reactive magnetron sputtering under unstable conditions using Plasma Emission Monitoring (PEM).

The chemical composition of the coatings was measured by Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy. The influence of the La/Ni ratio on the structure was checked by X-Ray Diffraction analyses.