Theoretical Screening of Transition Metal Single Atoms Anchored on γ-Graphyne as Electrocatalysts for Nitrogen Reduction Reaction

Ammonia (NH₃) plays an important role in the world economy and its demand is steadily rising alongside the progress of modern society. The electrocatalytic nitrogen reduction reaction (NRR) is presently regarded as a high-potential method for the synthesis of NH₃. Nevertheless, the development of efficient NRR electrocatalysts remains a challenging task. In this study, various transition metal (TM) single atoms (TM=Sc–Zn, Y–Cd except Tc, and Ta–Pt) anchored on γ-graphyne (γ-GY) are systematically investigated as NRR electrocatalysts using density functional theory (DFT) calculations. According to several criteria regarding the adsorption stability of isolated TM single atoms on γ-graphyne, the adsorption properties of N₂ on these TM single atoms, the adsorption competition between N₂ and H, and the free energy change in the initial protonation process for N₂, we find that Os@γ-GY and Re@γ-GY may be suitable electrocatalysts for NRR, and analyze the reasons why the two types of single atoms can well adsorb and activate N₂ molecules. From the reaction pathways of NRR catalyzed by the two single-atom systems, we further find that NRR is hindered by the step of *NH₂ hydrogenation to *NH₃ on Re@γ-GY but can proceed well on Os@γ-GY. Thus, Os@γ-GY behaves best in catalyzing NRR among the γ-GY anchored single atom systems studied. This work has the potential to offer valuable recommendations for the development of novel and highly effective NRR electrocatalysts.