Investigating Why Sulfurization Can Greatly Improve Ethanol Selectivity for Carbon Dioxide Electroreduction

Abstract

Carbon dioxide (CO2) electroreduction of products using renewable electricity sources is a promising avenue for chemical energy storage that is attracting increasing attention. Considerable effort has been focused on improving the activity and selectivity for CO2 electroreduction of C2+ products, especially for ethanol. However, studies of this process's underlying mechanism are still lacking. Herein, we use operando Raman spectroscopy combined with density functional theory (DFT) calculations to reveal mechanisms that explain why sulfurization can greatly improve ethanol selectivity for CO2 electroreduction. We found that the Faradaic efficiency (FE) of ethanol increased from 15% to 55% when the Ag-Au-Ag nanorods (NRs) were sulfurized to a Au-Ag-S NRs structure, which is an increase of over three times. Operando electrochemical surface-enhanced Raman spectroscopy empowered by 12C/13C isotope exchange finds that intermediates of CO2− and CO on the sulfurized Au-Ag-S NRs can greatly facilitate CO-CO coupling and improve ethanol selectivity. DFT calculations show that the Au-Ag-S NR structure, compared with the Ag-Au-Ag NRs, can lower the energy barrier for CO-CO coupling combined with a proton, greatly facilitating the ethanol formation. Therefore, sulfurization is an effective way to improve ethanol selectivity for CO2 electroreduction that can provide an important strategy to improve the selectivity for other reactions.