A tandem effect of atomically isolated copper–nitrogen sites and copper clusters enhances CO ₂ electroreduction to ethylene

Direct electrochemical conversion of CO₂ to C₂H₄ with high selectivity is highly desirable for lowering CO₂ emissions. However, limited by the slow *CO dimerization step at a single active site, it is difficult for current electrocatalysts to further improve the selectivity toward C₂H₄. Here we report a tandem catalyst PDI-Cu/Cu with Cu-N sites and Cu clusters, synthesized by uniformly dispersing Cu clusters on a coordination polymer PDI-Cu, which has atomically isolated Cu-N sites. This tandem catalyst, which has an optimal content of Cu clusters, shows more than 2 times the enhancement in C₂H₄ production compared with that of the non-tandem catalyst PDI/Cu. Density functional theory (DFT) calculations support the tandem reaction mechanism, where Cu-N sites first reduce CO₂ into highly concentrated CO and then the CO migrates to the surfaces of Cu clusters for further conversion into C₂H₄, decoupling the complex C₂H₄ generation pathway at single active sites into a two-step tandem reaction. This work offers a rational approach to design electrocatalysts for further boosting the selectivity of the CO₂RR to C₂₊ products via a tandem route.