Electronic Origin of Enhanced Selectivity through the Halogenation of a Single Mn Atom on Graphitic C<sub>3</sub>N<sub>4</sub> for Electrocatalytic Reduction of CO<sub>2</sub> from First-Principles Calculations
Renna Shakir, Hannu‐Pekka Komsa, Amit Sinha, J. Karthikeyan
Abstract
The electrochemical reduction of CO 2 to valuable products is a critical process that can potentially address energy and environmental challenges. Single-metal atom catalysts have gained significant attention because of their high efficiency and potential to mitigate the challenges associated with traditional-metal nanocatalysts. In particular, non-precious-metal-based catalysts are of great interest because of their low cost and abundance in the Earth’s crust. This work is a comprehensive study to reveal the role of halogen X (X = F, Cl, Br, and I) in improving the CO 2 reduction activity and selectivity of single manganese atom-based active sites on a graphitic carbon nitride (g-C 3 N 4 ) monolayer. Although previous experiments prove that halogenation improves the selectivity of a single Mn-atom-based catalyst, our calculations reveal the reason for the selectivity of the catalyst. The halogen-modified MnN 6 active site on g-C 3 N 4 has a high hydrogen evolution reaction (HER) tolerance. Hence, the selectivity due to the increased electronic stability originated from half-filled d orbitals of the Mn atom stabilized on g-C 3 N 4 . Also, we present the Gibbs free energy profile, onset potential ( U Min ), and overpotential (η) for various C 1 products (CO, HCOOH, CH 3 OH, and CH 4 ) at the active sites with and without halogenation. These results suggest that the MnN 6 active site of Mn-X-decorated g-C 3 N 4 is a highly efficient and selective electrocatalyst for the CO 2 RR against the HER. Our study provides directions for the design of a new CO 2 RR catalyst with improved selectivity and efficiency.