Ammonia (NH3),as one of the most necessary chemical materials,is mainly produced via the Haber-Bosch process from hydrogen (H2) and nitrogen (N2),which requires harsh synthesis conditions and aggravates energy consumption and greenhouse effect [1].As an alternative,electrocatalytic N2 reduction to NH3 has evolved for years.However,most of electrocatalysts are confined to poor NH3 synthesis effi-ciency restricted by the strong N≡N triple bonds,the com-petition of hydrogen evolution reaction (HER),and limited N2 solubility in H2O [2].In the exploration for an alternative nitrogen source except N2 to synthesize NH3,the nitrate anion (NO3-) brings about extensive attention because the dissociation energy of N=O bonds (204 kJ mol- 1) is lower than N≡N triple bonds [3],and the enrichment of NO3- in water resources causes the environmental pollution and further infringes the human health [4].Thus,selective con-version from NO3-to NH3 through the eight-electron re-duction,if proceeding under ambient conditions in the H2O-based system,may offer a green technology for the NH3 manufacture and simultaneously alleviate the energy and pollution problems.