Interfacial Tandem Catalysis Over a CuSn(OH)6/Co Heterostructure Enables Efficient Electroreduction of Nitrate to Ammonia.

Electrochemical nitrate reduction reaction (NO3 -RR) enables sustainable ammonia (NH3) production but is constrained by sluggish kinetics due to the high stability of NO3 - and insufficient hydrogenation of nitrogenous intermediates, where the initial NO3 - → NO2 - conversion is the rate-determining step (RDS). Herein, we report a CuSn(OH)6/Co heterostructure designed via an interfacial tandem-catalysis strategy to address both the kinetic bottleneck and downstream hydrogenation steps in a coordinated manner. In this architecture, CuSn(OH)6 activates NO3 - and then selectively catalyzes its conversion into *NO2, thereby overcoming the RDS limitation. Meanwhile, Co nanoparticles promote rapid H2O dissociation to generate abundant *H for subsequent hydrogenation reactions. Further investigations reveal that the heterointerface enables efficient directional transfer of *NO2 intermediate from CuSn(OH)6 to the Co component, promoting its complete reduction to NH3. Benefiting from this spatially and functionally integrated division of catalytic roles, the CuSn(OH)6/Co heterostructure exhibits a high NH3 yield of 64.51 µmol h- 1 mgCat - 1 and a selectivity of 92.28% at -0.7 V in 0.1 M NaSO4 containing 10 mM NaNO3, outperforming most reported catalysts. This work highlights a tandem-catalysis strategy that synchronously regulates RDS and hydrogenation pathways for sustainable NH3 production via NO3 -RR.