CO 2 ‐Mediated Dynamic Site Modulation in Copper Catalysts for Selective Electrocatalytic Nitrite‐to‐Ammonia Conversion

Abstract 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–N 4 ), cluster embedded (Cu–N 4 /Cu x ), and nanoparticle (Cu–NPs)—how CO 2 chemisorption differentially engineers active sites to optimize nitrite‐to‐ammonia conversion is unraveled. Systematic evaluations demonstrate CO 2 ’s tripartite role: 1) Stabilizing * NOOH intermediates through electronic modulation (Bader charge analysis), 2) Suppressing hydrogen evolution via site‐specific blocking ( * COO⁻ on Cu–N 4 , * CO on Cu–NPs; in situ Raman), and 3) Reducing the NO 2 → NOOH barrier on Cu–NPs (ΔG‡ = 0.34 eV by DFT). The synergistic Cu–N 4 /Cu x configuration achieves 94.5% NH 3 Faraday efficiency (FE) and yield rate (3236 µg h −1 cm −2 ) under CO 2 , substantially outperforming isolated components (Cu–N 4 : 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–N 4 sites preferentially adsorb * COO⁻ to impede hydrogen evolution reaction (HER), while Cu–NPs leverage * CO intermediates to accelerate * NO 2 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.