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

Direct electrochemical conversion of CO 2 to C 2 H 4 with high selectivity is highly desirable for lowering CO 2 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 C 2 H 4 . 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 C 2 H 4 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 CO 2 into highly concentrated CO and then the CO migrates to the surfaces of Cu clusters for further conversion into C 2 H 4 , decoupling the complex C 2 H 4 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 CO 2 RR to C 2+ products via a tandem route.