Unlocking the Distance Effect on CO2 Electroreduction to Multi-Carbon Products via Monolayer Model Catalysts.

The interaction between adjacent active sites significantly influences electrocatalytic performance, for example, CO2 electroreduction (CO2RR), yet quantifying this effect experimentally remains challenging due to the difficulty in precisely controlling inter-site distances. Here, we construct a monolayer model catalyst using Cu-coordinated porphyrins with well-defined Cu-N4 sites on Au(111). The distance between Cu centers is regulated at the sub-nanometer level by modifying molecular ligands and aggregation states, and is directly measured by scanning tunneling microscopy (STM). This adjustable spacing critically determines the selectivity toward multi-carbon products in CO2RR. When Cu sites are spaced 0.98 nm apart,a Faradaic efficiency (FE) of 6.1% for C2H4 is achieved. Increasing the inter-distance of Cu sites to 1.50 nm dramatically reduces C2H4 FE to 1.2%. At larger separations of 1.63 nm and 1.74 nm, C─C coupling is almost completely suppressed, and C2H4 production becomes negligible. These results provide direct experimental evidence of the distance effect in CO2 electroreduction, and precisely identify, for the first time, the distance between Cu sites capable of facilitating C─C coupling process. This study establishes a molecular-level platform for probing fundamental mechanisms in electrocatalysis.