The invention provides for a stable materials system for intermediate temperature solid oxide fuel cells (SOFC). Without limitation, a solid electrolyte layer can include a Sr-and-Mg doped lanthanum gallate layer, such as La.sub.0.9Sr.sub.0.1Ga.sub.0.8Mg.sub.0.2O.sub.3, (LSGM), or a bi-layer semiconductor electrolyte (comprising, for example, donor doped SrTiO3 in an n-type first semiconductor layer and LSCF or LSM in a p-type second semiconductor layer); cathode materials can include La.sub.1-xSr.sub.xMnO.sub.3 (LSM), La.sub.1-xSr.sub.xCo.sub.yFe.sub.1-yO.sub.3 (LSCF), a two-phase particulate composite consisting of LSM and LSGM (LSM-LSGM), and LSCF-LSGM composite; anode materials can include Ni--Ce.sub.0.85Gd.sub.0.15O.sub.2 (Ni-GDC) and Ni--Ce.sub.0.6La.sub.0.4O.sub.2 (Ni-LDC) composites; and a barrier layer of GDC or LDC can be used between the electrolyte and Ni-composite anode to prevent adverse reaction of the Ni in the anode layer with lanthanum in the electrolyte layer.
STATEMENT AS TO FEDERALLY SPONSORED RESEARCH
 This invention was made with Government Support under Contract Number DE-FG26-02NT41539 awarded by the Department of Energy. The Government has certain rights in the invention.