Chemical reactions between the superior perovskite oxide-ion conductor Sr- and Mg-doped LaGaO3 (LSGM). CeO2, and NiO have been studied by powder X-ray diffraction. The results showed that an extensive reactivity occurs a result of La migration driven by a gradient of La chemical activity. La migration across the LSGM/electrode interfaces in a fuel cell leads re, the formation of resistive phases at the interface, either LaSrGa3O7 or LaSrGaO4. Use of 40 mol % La2O3-doped CeO2 as an interlayer between anode and electrolyte as well as in the NiO-containing anode prevents all reactions found. Consequently, the air-H-2 cell maximum power density was increased to nearly 900 mW/cm(2) at 800 degreesC with a 600 mum thick LSGM electrolyte. No sign of degradation was observed at 800 degreesC over 2 weeks for an interlayered cell under a loading current density of 250 mA/cm(2).