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.