1.Introduction
Ammonia(NH3)is not only an important chemical in many fields,but also provides a promising intermediate for energy stor-age[1,2].To produce NH3 from naturally abundant N2,the strong N≡N bond in the inert N2 molecules must be broken firstly.Elec-trochemical nitrogen reduction reaction(N2RR)under ambient conditions holds the great promise to directly produce NH3 from abundant N2 and renewable electricity in aqueous solutions[3-13].