Electronic Origin of Enhanced Selectivity through the Halogenation of a Single Mn Atom on Graphitic C₃N₄ for Electrocatalytic Reduction of CO₂ from First-Principles Calculations

The electrochemical reduction of CO2 to valuableproductsis a critical process that can potentially address energy and environmentalchallenges. Single-metal atom catalysts have gained significant attentionbecause of their high efficiency and potential to mitigate the challengesassociated with traditional-metal nanocatalysts. In particular, non-precious-metal-basedcatalysts are of great interest because of their low cost and abundancein the Earth's crust. This work is a comprehensive study toreveal the role of halogen X (X = F, Cl, Br, and I) in improving theCO(2) reduction activity and selectivity of single manganeseatom-based active sites on a graphitic carbon nitride (g-C3N4) monolayer. Although previous experiments prove thathalogenation improves the selectivity of a single Mn-atom-based catalyst,our calculations reveal the reason for the selectivity of the catalyst.The halogen-modified MnN6 active site on g-C3N4 has a high hydrogen evolution reaction (HER) tolerance.Hence, the selectivity due to the increased electronic stability originatedfrom half-filled d orbitals of the Mn atom stabilized on g-C3N4. Also, we present the Gibbs free energy profile, onsetpotential (U (Min)), and overpotential (& eta;)for various C-1 products (CO, HCOOH, CH3OH, andCH(4)) at the active sites with and without halogenation.These results suggest that the MnN6 active site of Mn-X-decoratedg-C3N4 is a highly efficient and selective electrocatalystfor the CO2RR against the HER. Our study provides directionsfor the design of a new CO2RR catalyst with improved selectivityand efficiency.