Ammonia is an important chemical feedstock and is produced by Ru or Fe catalyst so far. We investigated Co catalyst for low temperature ammonia synthesis in an electric field. Well-reduced Co/Ce0.5Zr0.5O2 catalyst showed high activity for ammonia synthesis even at 473 K in the electric field. Various characterizations including kinetic tests, operando DRIFTS measurements, TEM observations, and XAFS measurements, revealed that the active site is the interface between supported Co and Ce0.5Zr0.5O2 oxide support, thanks to the surface protonics derived from an electric field. [GRAPHICS] .