Perovskite-type oxides BaCe 0.90 Sm 0.10 O 3Àd (BCS) and BaCe 0.80 Gd 0.10 Sm 0.10 O 3Àd (BCGS) were synthesized by the sol-gel method and characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Using the sintered samples as solid electrolytes and silver-palladium alloy as electrodes, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid-state proton-conducting cell reactor. The maximum rate of production of ammonia was 5.82 Â 10 À9 mol s À1 cm À2 .