Prognostication of two-dimensional transition-metal atoms embedded rectangular tetrafluorotetracyanoquinodimethane single-atom catalysts for high-efficiency electrochemical nitrogen reduction.

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 (N) fixation into ammonia (NH) 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-rFTCNQ) 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-rFTCNQ, were obtained. Among them, Ti-rFTCNQ catalyzing the N reduction to NH through an enzymatic mechanism needs a theoretical onset potential of only -0.41 V. When Mo-rFTCNQ 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 N adsorption, the differential charge density, and the spin density reveals that the Ti-, Mo-, Nb-, and Tc-rFTCNQ monolayers all can effectively adsorb and activate inert N, which may be mainly attributed to the "acceptance-donation" interaction between TM and N.