Electronic Structure Tailoring of Copper by Oxygen-Enriched Carbon Dots Enables Nitrate-to-Ammonia Electrosynthesis via *NO2 Decoupling.

The electrochemical nitrate reduction reaction (NITRR) represents a sustainable strategy for ambient ammonia synthesis. However, copper-based catalysts often suffer from excessive adsorption of the *NO2 intermediate due to the high electron density on the Cu surface, resulting in active-site poisoning and sluggish reaction kinetics. Achieving an optimal balance between *NO2 adsorption and activation remains a major challenge for efficient nitrate reduction. Herein, we design a NITRR electrocatalyst consisting of oxygen-enriched carbon dots (CDs) and a carbon layer encapsulating copper nanoparticles (CuCECDs). Benefiting from the optimized decoupling of *NO2, the catalyst achieves an outstanding ammonia yield rate of 2.5 mol. gcat-1 h-1 with a Faradaic efficiency (FE) of 85% at -0.5 V versus RHE. Combined experimental and theoretical studies demonstrate that the oxygen-enriched carbon dots effectively regulate the electronic structure of Cu, weakening the excessive adsorption of *NO2 while confining its subsequent conversion within the carbon layer, thereby promoting efficient *NO2 transformation (*NO2 decoupling). Moreover, the carbon shell induces lattice strain in the Cu nanoparticles (Cu NPs), facilitating water dissociation and hydrogen generation, which further enhances ammonia electrosynthesis performance.