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-po-tential 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.