Dynamically Stable Cu0Cuδ+ Pair Sites Based on In Situ-Exsolved Cu Nanoclusters on CaCO3 for Efficient CO2 Electroreduction.

Copper-based catalysts are the choice for producing multi-carbon products (C2+) during CO2 electroreduction (CO2RR), where the Cu0Cuδ+ pair sites are proposed to be synergistic hotspots for C-C coupling. Maintaining their dynamic stability requires precise control over electron affinity and anion vacancy formation energy, posing significant challenges. Here, we present an in-situ reconstruction strategy to create dynamically stable Cu0Cu0.18+OCa motifs at the interface of exsolved Cu nanoclusters and CaCO₃ nanospheres (Cu/CaCO₃). In-situ XAFS analysis confirmed the low-valency state of Cuδ+ during CO2RR. DFT calculations demonstrated that the nanocluster size arises from the balance between metal-support interactions and Cu-Cu cohesive energy, while the dynamic stability of rich interfacial Cuδ+ sites is attributed to their low electron affinity and high CO32- vacancy formation energy, which collectively contribute to reduced reducibility. The transformed Cu/CaCO₃ exhibits an impressive C2+ Faradaic efficiency of 83.7% at a partial current density of 393 mA cm-2, facilitated by adsorption of *CO with varying electronegativity at heterogeneous copper sites that lowers the C-C coupling energy barrier. Our findings establish insoluble carbonate as an effective anion pairing for Cu0Cuδ+ sites, highlighting the effectiveness of the in-situ reconstitution strategy in producing a high density of dynamically stable Cu0Cuδ+ pair sites.