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

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Interactions between adjacent active sites are crucial for electrocatalytic performance, particularly in CO2 electroreduction (CO2RR).
• Experimentally controlling and quantifying the effect of inter-site distance in electrocatalysis is challenging.

Purpose of the Study:

• To construct a model catalyst with precisely controlled inter-site distances between copper (Cu) active centers.
• To investigate the effect of Cu-Cu distance on CO2RR selectivity, especially for multi-carbon products.

Main Methods:

• Fabrication of a monolayer model catalyst using Cu-coordinated porphyrins with Cu-N4 sites on Au(111).
• Tuning inter-site distances at the sub-nanometer level via molecular ligand modification and aggregation control.
• Direct measurement of inter-site distances using scanning tunneling microscopy (STM).
• Electrochemical evaluation of CO2RR performance, including Faradaic efficiency (FE) for C2H4.

Main Results:

• Adjustable Cu-Cu spacing was achieved and measured, ranging from 0.98 nm to 1.74 nm.
• Optimized Cu spacing of 0.98 nm yielded a C2H4 FE of 6.1%.
• Increasing Cu-Cu distance to 1.50 nm significantly reduced C2H4 FE to 1.2%.
• Larger separations (1.63 nm and 1.74 nm) nearly suppressed C-C coupling and C2H4 production.

Conclusions:

• Direct experimental evidence confirms the critical role of inter-site distance in CO2 electroreduction selectivity.
• The study identifies the specific Cu-Cu distances that facilitate C-C coupling for multi-carbon product formation.
• A molecular-level platform was established for fundamental mechanistic studies in electrocatalysis.