Unraveling the Size-Dependent Effect of Cu Cluster on CO Reduction Insight from Theory.

Atomically dispersed and cluster copper (Cu) catalysts anchored on nitrogenated holey carbon frameworks have garnered increasing attention as promising platforms for the electrochemical CO reduction reaction (CORR), yet the structural evolution and mechanistic origin of selectivity and C-C coupling on Cu clusters remain elusive. Herein, we performed a comprehensive first-principles study of Cu clusters supported on CN substrates to elucidate their structural stability, electronic properties, and catalytic behavior toward C-C products. The Cu atoms stably bind to N sites, evolving from planar to 3D configurations with an increasing cluster size. We demonstrated that the Cu-N interfacial synergy in Cu@CN promoted CH selectivity via enabling dynamic interconversion of the key intermediate *CHO between Cu and N sites. Moreover, we revealed that a dynamic *CO generation-migration-regeneration cycle, driven by apex-basal site synergy in Cu@CN, facilitates multi-*CO accumulation, essential for C-C coupling. Elevated *CO coverage lowers the hydrogenation barrier, enabling efficient *CHO-*CHO coupling (0.34 and 0.41 eV, respectively) and promoting alkane-type C product (such as CH and CH) formation on Cu@CN. These results provide atomic-scale insights into Cu cluster catalysts and design principles for nitrogen-carbon-supported C-C coupling catalysts.