Abstract: Electrocatalytic nitrate reduction reaction (NO₃RR), as a green technology for producing ammonia and purifying wastewater, faces challenges in terms of nitrite intermediate accumulation and competitive hydrogen evolution reactions. Tandem catalytic strategy (NO₃^-→NO₂^-→NH₃) is expected to significantly improve the rate and selectivity of ammonia production. Therefore, designing and constructing dual active sites with different catalytic properties contributes to improving reaction activity. Herein, a CuNi bimetallic metal organic frameworks (MOFs) tandem catalytic system using well-defined MOFs as templates was constructed through simple hydrothermal synthesis. The research results indicated that Cu active sites could efficiently catalyze the reduction of NO₃^- to NO₂^-, while Ni sites exhibited excellent active hydrogen species ^*H supply capacity and NO₂^- conversion efficiency, forming an efficient tandem catalytic mechanism with Cu sites, achieving a Faraday efficiency of up to 90.1% for ammonia synthesis and an ammonia yield of 28.8 mg·h^-1·mg_cat^-1. In addition, the bimetallic MOFs catalyst showed excellent cycling stability without any degradation in ammonia synthesis after multiple cycling tests. This work provides new insights for the design and optimization of high-performance tandem catalysts.

Key words: ammonia production, nitrate reduction reaction, bimetallic, metal organic framework, tandem catalysis