Sm and S Co-doping to Construct Homo-hetero Cu Catalysts for Synergistic Enhancing CO₂ Electroreduction

Copper (Cu) is recognized as one of the most efficient metal catalysts that can perform the electrocatalytic CO2 reduction reaction (CO2RR) and its surface oxidation state determines the reaction pathway. The Cud+ (0 < d < 1) species, are well known active sites in CO2RR to produce hydrocarbons and oxygenates. However, Cud+ active sites are difficult to control, and it is very easy to be reduced to Cu-0 under CO2RR operating conditions. Herein, we report a homo-hetero doping strategy to construct an efficient samarium (Sm) and sulfur (S) co-doping catalyst (Sm-x-CuSy) for CO2RR to formic acid (HCOOH). At optimum conditions, Sm-x-CuSy delivered a high HCOOH Faradaic efficiency (FE) of 92.1% at the current density of 300 mA.cm(-2) using 1 mol/L KOH aqueous solution as electrolyte, and the reduction potential was as low as -0.52 V vs. reversible hydrogen electrode (RHE). The co-doping of Sm and S resulted in excellent CO2RR performance owing to the synergistic effect of the homo-hetero structure. The homo-doping of S could effectively adjust the electronic structure of Cu in favor of the formation of abundant Cud+ species. The existence of hetero-Sm species could not only stabilize the Cud+ sites, but also increase the concentration of H ions to form a favorable catalytic environment for HCOOH generation.