Insights into pyridine-based graphynes anchoring second-row transition metal single atoms for electrocatalytic CO2 reduction: a DFT study

Abstract

Single-atom catalysts have been widely used for the electroreduction of CO₂ (CO₂RR). In this study, density functional theory is employed to evaluate the electrocatalytic performance of pyridine-based graphyne anchoring second-row transition metal atoms (TM-pdGY) for the CO₂RR. The most stable configuration and corresponding structural attributes were obtained by structure optimization. The energy calculation results related to the structure show large bonding energies (−0.82 to −5.92 eV), comparatively high cohesive energies (−0.7 to −7.6 eV per atom) and moderate formation energies (−1.63 to 2.65 eV), indicating structural stability and feasibility of preparation. The results of electronic structure analysis also prove the existence of strong covalent bonds by revealing the frequent charge transfer and significant orbital hybridization between the metal atoms and the catalyst substrate. Competitive analysis between the CO₂RR and the hydrogen evolution reaction (HER) shows that all TM-pdGYs exhibit higher selectivity toward CO₂RR. Through Gibbs free energy graphs and reaction pathway diagrams of four C1 products, the most favorable products (CH₄ and HCOOH) of TM-pdGYs have been determined. It is demonstrated that the regulation of the overall electronic structure of the catalyst by the TM–N coordination structure is the origin of the high CO₂RR activity. It is worth noting that Ru/Rh/Pd/Cd-pdGYs possess higher CO₂RR activity because of their lower limiting potentials (U_L) (−0.51 to −0.88 V). These results indicate that second-row TM-pdGYs exhibit excellent performance for the CO₂RR.