Abstract: 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 La0.9Sr0.1Ga0.8Mg0.2O3, (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 La1-xSrxMnO3 (LSM), La1-xSrxCoyFe1-yO3 (LSCF), a two-phase particulate composite consisting of LSM and LSGM (LSM-LSGM), and LSCF-LSGM composite; anode materials can include Ni—Ce0.85Gd0.15O2 (Ni-GDC) and Ni—Ce0.6La0.4O2 (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.