Electrochemical synthesis of ammonia driven by clean energy is expected to realize the supply of ammonia for distributed production of industry and agriculture. Here, nickel nanoparticles and nickel in the form of single atoms were simultaneously anchored on the electrochemically active carrier BCN matrix through a structured domain strategy, which realized a high-efficiency, high-value-added, conversion of nitrate in sewage. Specifically, the electrochemical nitrate reduction reaction (NIRR) driven by BCN@Ni in alkaline media achieves an ammonia yield rate as high as 2320.2 mu g h(-1) cm(-2) (at-0.5 V vs RHE), and Faraday efficiency as high as 91.15% (at-0.3 V vs RHE). Even in neutral and acidic media, the ammonia yield rates of NIRR driven by BCN@Ni are as high as 1904.2 mu g h(-1) cm-2 and 2057.4 mu g h(-1) cm(-2), respectively (at-0.4 V vs RHE). The (NO3-)-N-15 isotope labeling experiment verified that the recorded ammonia all came from the electrochemical reduction of NO3- on BCN@Ni. Density functional theory (DFT) calculations show that both nano-Ni and single-atom Ni in BCN@Ni have the ability to electrochemically convert NO3- into NH3, and that the addition of BCN can further promote the NIRR on Ni.