Sn Atoms on Cu Nanoparticles for Suppressing Competitive H₂Evolution in CO₂Electrolysis

The electrochemical reduction of carbon dioxide (CO2) to chemical feedstocks is an attractive method for the removal of CO2 from the environment. Although copper (Cu)-based catalysts produce hydrocarbons with relatively high selectivity during CO2 electroreduction, such catalysts evolve a certain amount of H2 via proton reduction reactions. Because low-coordinated Cu sites are likely active for the competing hydrogen evolution reaction (HER), hindering such low-coordinated Cu sites by decoration with inert metal atoms is a promising approach to increasing the selectivity of the CO2 reduction reaction (CO2RR) over the HER. In the present study, we synthesized tin (Sn)-modified Cu nanoparticles with varied Sn ratios via a simple wet-chemical method. Physical and theoretical characterizations revealed that Sn atoms preferentially locate at the low-coordinated sites when Sn is present at low contents (less than 1.5%). Compared with the bare Cu catalyst, the Sn-modified Cu electrocatalyst shows suppression of the HER and acceleration of the carbon monoxide (CO) evolution reaction. The first-principles calculations about the adsorption strength of reaction intermediates revealed that low-coordinated Cu sites with the modification of Sn atoms exhibited lower activity for both HER and CO2RR than that without modification. As a result, the activity of coordinatively saturated Cu atoms, where the CO2RR is more favorable than the HER, was emphasized. The modification of trace foreign metals in metal nanoparticles may provide an avenue for the synthesis of selective electrocatalysts for various target reactions.