Electrosynthesis of NH3 from nitrate anion (NO3-) reduction (NO3-RR) is a cascade reaction, which is considered as a great potential alternative to the Haber-Bosch route to reduce CO2 emissions and alleviate the adverse effects of excessive NO3- contamination in the environment. Frequently, solid solution alloys (SSA) with a single-phase active site may struggle to fully utilize their benefits during the entire process of nitrate (NO3-) reduction, which involves multiple intermediate reactions. Here, we showed that by separating Cu and Ni in a Janus Cu@Ni catalyst structure, we can achieve excellent performances in NO3-RR, yielding a high Faradaic efficiency (92.5%) and production rate of NH3 (1127 mmol h-1 g-1) at -0.2 V vs. RHE, compared to CuNi SSA (82.6%, 264 mmol h-1 g-1). Here we demonstrate that a Janus Cu@Ni catalyst with short-range ordered catalytic sites, favours NO spillover from Cu-rich phase to Ni-rich phase and the adsorption of NO on the later active sites through a bridge-bond mode. This facilitates N-O bond cleavage, resulting in NH3 production rate nearly 5-times higher than that of CuNi SSA, where NO was linearly-bonded on its surface. Furthermore, a hydrogen spillover process was also observed, in which Ni dissociates H2O to generate *H which spontaneously migrates to adjacent catalytic sites to hydrogenate the *NOx intermediates. The study of this catalytic effect, a cooperative tandem enhancement, provides a new insight into the design of multifunctional heterogeneous catalysts for NH3 electrochemical synthesis.
