In Situ Reconstruction of Bimetallic MOFs to Form Copper-Cobalt Relay Catalysis for Efficient Nitrate Reduction to Ammonia.

The electrochemical nitrate reduction reaction (eNO3RR) is hindered by poor selectivity and sluggish kinetics due to competing hydrogen evolution and complex multi-electron/proton transfers. Here, a bimetallic CuCo-MOF （Metal-Organic Framework） is reported catalyst that undergoes in situ electrochemical reconstruction to form copper nanoparticles embedded within a cobalt-MOF matrix, establishing spatially coupled active sites for tandem catalysis. Mechanistic investigations reveal that the in situ-generated Cu nanoparticles selectively catalyze the nitrate-to-nitrite conversion, while the adjacent cobalt sites in the MOF framework facilitate water dissociation to provide reactive hydrogen species (*H) for subsequent nitrite hydrogenation to ammonia. The confined MOF architecture ensures efficient intermediate transfer, effectively preventing nitrite accumulation. This unique relay catalysis mechanism enables the reconstructed CuCo-DHTA catalyst to achieve remarkable NO3RR performance, including a Faradaic efficiency exceeding 95% across a wide potential window (-0.8 to -1.0 V vs RHE) and a record-high ammonia production rate of 20.02 mg h-1 cm-2, surpassing state-of-the-art MOF-based catalysts. The pre-catalyst's reconstruction strategy in this work provides a flexible design for high-performance nitrate reduction catalysts.