Potential-regulated CO migration and CC bond formation on a co single-atom/Fe3 cluster tandem catalyst for CO2 electroreduction.

The electrocatalytic reduction of CO2 toward C2 products offers a promising route for sustainable chemical synthesis but the formation and stabilization of C2 intermediates remain challenging. Herein, we theoretically design a tandem catalyst composed of a Co single atom and an Fe3 cluster co-anchored on N-doped graphene (CoN4-Fe3N6@G). Density functional theory (DFT) calculations reveal that the Fe3 site and Co site each generate one *CO species, after which *CO adsorbed at the Co site migrates to the Fe3 site, enabling a dual-*CO precursor for CC coupling. Potential-dependent free-energy analyses identify complementary potential windows: +0.3 V favors *CO retention and migration and dual-*CO precursor assembly and, once *CO···*CHO is present, CC bond formation relative to further proton-coupled electron transfer (PCET) hydrogenation; -0.9 V drives PCET conversion and further C₂ hydrogenation but also enhances C₁ hydrogenation and H adsorption. These findings motivate a pulsed-potential hypothesis that coordinates intermediate retention and assembly with cathodic conversion. This work provides mechanistic insights into atom-cluster tandem catalysts for promoting C2-intermediate formation in CO2 electroreduction.