De Novo Engineering High-Density Proximal Copper Single Atoms for Enhanced C─C Coupling in CO₂ Electroreduction

Copper-based single-atom catalysts (SACs) are promising for the electrochemical CO₂ reduction reaction, yet their multicarbon production remains restricted by the inherent trade-off among atomic loading, dispersion, and proximity required for efficient C─C coupling. In this study, we develop a de novo coordination-site and geometry engineering strategy to construct high-density proximal Cu SACs for improving CO₂-to-C₂₊ electroreduction. Flexible molecular building blocks rich in N/O coordination motifs assemble into wrinkled 2D networks and further hierarchically organize into a 3D nanoflower framework, where isolated Cu sites with high loading of 14 wt% are anchored via robust N/O coordination. The structural bending brings adjacent Cu atoms into close proximity (∼2.6 Å). Competitive N/O coordination generates asymmetric and low-coordinated microenvironments, promoting *CO intermediate stabilization and subsequent C─C coupling. The optimized catalyst achieves a C₂₊ Faradaic efficiency of 81.34% at 500 mA·cm^-2, including 51% ethylene selectivity, with stable operation exceeding 100 h. This work sheds light on structural dimensional control and microenvironment engineering for promoting cooperative catalysis in single-atom systems, offering new opportunities for efficient multicarbon electrosynthesis.