CO2‐Mediated Dynamic Site Modulation in Copper Catalysts for Selective Electrocatalytic Nitrite‐to‐Ammonia Conversion

The rational modulation of catalytic sites to steer multi‐step reaction pathways remains pivotal yet challenging in electrochemical ammonia synthesis. Herein, by investigating three representative copper configurations—single atom (Cu–N4), cluster embedded (Cu–N4/Cux), and nanoparticle (Cu–NPs)—how CO2 chemisorption differentially engineers active sites to optimize nitrite‐to‐ammonia conversion is unraveled. Systematic evaluations demonstrate CO2’s tripartite role: 1) Stabilizing *NOOH intermediates through electronic modulation (Bader charge analysis), 2) Suppressing hydrogen evolution via site‐specific blocking (*COO⁻ on Cu–N4, *CO on Cu–NPs; in situ Raman), and 3) Reducing the NO2 → NOOH barrier on Cu–NPs (ΔG‡ = 0.34 eV by DFT). The synergistic Cu–N4/Cux configuration achieves 94.5% NH3 Faraday efficiency (FE) and yield rate (3236 µg h−1 cm−2) under CO2, substantially outperforming isolated components (Cu–N4: 78.1% FE/2100 µg h−1 cm−2; Cu–NPs: 88.6% FE/5100 µg h−1 cm−2). Operando analysis reveals mechanistic divergence: Single‐atomic Cu–N4 sites preferentially adsorb *COO⁻ to impede hydrogen evolution reaction (HER), while Cu–NPs leverage *CO intermediates to accelerate *NO2 hydrogenation. This atomic‐level understanding of chemisorption‐driven site regulation establishes a generalizable design principle for decoupling activity and selectivity constraints, advancing sustainable nitrogen electrochemistry.