Constructing Monolayer Model Catalysts to Uncover the Distance Effect on CO2 Electroreduction towards Multi-Carbon Products

Abstract The interaction between adjacent active sites has significant effect on the performance of various electrocatalysis, e.g., CO₂ electroreduction. Unfortunately, little experimental work has been done to quantify this effect, due to the huge challenge in accurately regulating the distance between active sites. Herein, Cu-coordinated porphyrins with clear Cu–N₄ active sites are introduced as platform molecules to construct a monolayer structure on the Au(111) substrate. The distance between Cu centers can be accurately regulated in subnanometer level via changing the molecular ligands and the state of aggregation, and directly measured by scanning tunneling microscope (STM). The adjustable distance between adjacent Cu sites can bring forth fundamentally different selectivity of multi-carbon products in CO₂ electroreduction. Specifically, Cu sites with 0.98 nm inter-distance can still generate an appreciable 6.1% faraday efficiency (FE) of C₂H₄, and then drop dramatically to 1.2% with a 1.50 nm inter-distance. When the inter-distances between Cu sites are furtherly increased to 1.63 and 1.74 nm, the C − C coupling pathway will be totally blocked and thereby the selectivity of C₂H₄ will decline to almost negligible levels. These experimental results directly demonstrate the distance effect on CO₂ electroreduction for the first time. In addition, theoretical calculations also demonstrate a strong correlation between inter-site distance and selectivity of C₂H₄. This work might inspire the design of model catalysts to investigate the fundamental mechanism of various electrocatalytic reactions.