In situ formation of highly dispersed 2-5 nm Ru nanoparticles was successfully achieved in highly Ru-doped (40% Ru) perovskite cathode material, Ru-doped La0.3Sr0.6TiO3 (LSTR), used for electrochemical ammonia synthesis in a proton-conducting fuel cell (PCFC). Highly dispersed Ru nanoparticles were observed by exsolution of doped Ru from the B-site in the LSTR perovskite lattice under PCFCs operating conditions, that is, a reducing atmosphere, without agglomeration, which is difficult to achieve with a conventional impregnation method. The particle size and dispersion were successfully controlled by reduction temperature and Ru doping amount. The optimized microstructure was finally adopted for the electrochemical synthesis of ammonia with BaCe0.9Y0.1O3 solid electrolyte at 500 A degrees C. Ammonia formation using a 40% Ru-doped LSTR (LSTR40) cathode was observed by applying cathodic overpotentials. The maximum ammonia formation rate using the LSTR40 cathode was 3.8 x 10(-12) mol s(-1) cm(-2) at -0.1 V. The results suggest that Ru nanoparticles exsoluted from the LSTR perovskite act as a active site effectively for the electrochemical reaction.