Steering CO₂ electroreduction to hydrocarbons over 2D thiol-based conductive metal-organic framework

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Electrocatalytic CO2 reduction (CO2RR) primarily yields simple two-electron products like CO and HCOOH.
• Achieving multiple-electron transferred hydrocarbon products from CO2RR remains a significant challenge.
• The specific role of sulfur atoms in CO2RR catalysis, activity, and selectivity is not well understood.

Purpose of the Study:

• To develop a novel catalyst for CO2RR with enhanced selectivity towards hydrocarbon products.
• To investigate the catalytic activity and product selectivity of a defined Cu-S4 active site.
• To elucidate the mechanism by which sulfur atoms influence CO2RR.

Main Methods:

• Synthesis of a conductive two-dimensional metal-organic framework, Cu3(THT)2, featuring Cu-S4 active sites.
• Electrochemical evaluation of Cu3(THT)2 for CO2RR, comparing its performance to a Cu-N4 precursor (Cu3(HITP)2).
• Theoretical calculations to understand the interaction between the catalyst active site and reaction intermediates.

Main Results:

• Cu3(THT)2 predominantly produces methane (CH4), a deep reduction product, unlike Cu3(HITP)2 which favors CO.
• Cu3(THT)2 achieved 63.5% Faradaic efficiency for CH4 at -1.4 V vs RHE, with a high current density of -298.3 mA cm-2.
• Theoretical studies revealed that electron-rich Cu-S4 sites stabilize the *CO intermediate more effectively than Cu-N4 sites, with sulfur atoms forming stabilizing interactions.

Conclusions:

• This study demonstrates the first successful use of non-metallic sulfur centers in a catalyst to significantly enhance and tune product selectivity in CO2RR.
• The Cu-S4 active sites in Cu3(THT)2 are highly effective for the electrocatalytic reduction of CO2 to CH4.
• The findings highlight the potential of sulfur-containing catalysts for advanced CO2 conversion.