Selectivity of CO2 reduction reaction to CO on the graphitic edge active sites of Fe-single-atom and dual-atom catalysts: A combined DFT and microkinetic modeling

We study the carbon dioxide reduction reaction (CO2RR) activity and selectivity of Fe single-atom catalyst (Fe-SAC) and Fe dual-atom catalyst (Fe-DAC) active sites at the interior of graphene and the edges of graphitic nanopore by using a combination of DFT calculations and microkinetic simulations. The trend of limiting potentials for CO2RR to produce CO can be described by using either the adsorption energy of COOH, CO, or their combination. CO2RR process with reasonable reaction rates can be achieved only on the active site configurations with weak tendencies toward CO poisoning. The efficiency of CO2RR on a catalyst depends on its ability to suppress the parasitic hydrogen evolution reaction (HER), which is directly related to the behavior of H adsorption on the catalyst’s active site. We find that the edges of the graphitic nanopore can act as potential adsorption sites for an H atom, and in some cases, the edge site can bind the H atom much stronger than the main Fe site. The linear scaling between CO and H adsorptions is broken if this condition is met. This condition also allows some edge active site configurations to have their CO2RR limiting potential lower than the HER process favoring CO production over H2 production.