Covalent Organic Frameworks on Cu₂O Nanocubes as Rapid Proton/Electron Transfer Gates for Efficient NH₃...

Nitrate electroreduction to ammonia offers a dual opportunity: decarbonizing NH₃ production by replacing the energy-intensive Haber-Bosch process and remediating nitrate-contaminated wastewater. While copper-based catalysts show promise for this transformation, their practical implementation is hindered by sluggish kinetics and competing hydrogen evolution pathways. Here, we report the integration of covalent organic framework (COF) layers onto a Cu₂O surface, which enables rapid proton/electron transfer and substrate activation for efficient NH₃ electrosynthesis from NO₃^- in neutral media. By growing pyridine- or imidazole-decorated COF shells with varying thickness on Cu₂O nanocubes, we achieve precise control over the microenvironment of the electrocatalyst surface. The pyridine-COF on Cu₂O demonstrates 84% Faradaic efficiency for NH₃ production with 92.11% selectivity and a record yield of 2.3 mg h^-1 cm^-2. In situ spectroscopic investigations reveal that the COF shells have multifunctional roles: they selectively transport reactants, stabilize key intermediates through hydrogen bonding interactions, and steer the reaction along an associative pathway that bypasses common side reactions. Our findings establish COF-gated core-shell architectures as a generalizable platform for designing efficient, selective, and durable electrocatalysts for broad applications.