Prognostication of two-dimensional transition-metal atoms embedded rectangular tetrafluorotetracyanoquinodimethane...

Extensive investigations on the electrocatalytic nitrogen reduction reactions (eNRR) and the high-efficiency single-atom catalysts (SACs) have increasingly given us confidence in intensive arrival of nitrogen (N₂) fixation into ammonia (NH₃) under ambient conditions in the future, which prompts us to speed up the exploration for highly active SACs for eNRR. Excellent SACs in eNRR should have three advantages: high selectivity, low overpotential, and high stability. Based on these aspects, we employed high-throughput screening method and first-principles calculations to study the catalytic performance of 30 transition-metal atoms (TMs) embedded rectangular tetrafluorotetracyanoquinodimethane (denoted as TM-rF₄TCNQ) monolayers (TM = 3d, 4d, and 5d series transition metal atoms) for the eNRR process, and four potential catalysts, i.e., Ti-, Mo-, Nb-, and Tc-rF₄TCNQ, were obtained. Among them, Ti-rF₄TCNQ catalyzing the N₂ reduction to NH₃ through an enzymatic mechanism needs a theoretical onset potential of only -0.41 V. When Mo-rF₄TCNQ catalyzes eNRR through a distal mechanism, the theoretical onset potential is as low as -0.43 V. The band structures show that these materials are all metallic, ensuring good charge transport during the eNRR process. Analyzing the projected density of states (PDOSs) before and after N₂ adsorption, the differential charge density, and the spin density reveals that the Ti-, Mo-, Nb-, and Tc-rF₄TCNQ monolayers all can effectively adsorb and activate inert N₂, which may be mainly attributed to the "acceptance-donation" interaction between TM and N₂.