Electrochemical ammonia synthesis under ambient conditions using TM-embedded porphine-fused sheets as single-atom catalysts.

In this research, we systematically investigated the reaction mechanism and electrocatalytic properties of transition metal anchored two-dimensional (2D) porphine-fused sheets (TM-Por) as novel single-atom catalysts (SACs) for the electrochemical nitrogen reduction reaction (eNRR) under ambient conditions. Using high-throughput screening and first-principles calculations based on the density functional theory (DFT) method, three eNRR catalyst candidates, i.e. Mo-Por, Tc-Por, and Nb-Por, were screened out, with the eNRR onset potentials on them being -0.36, -0.53, and -0.74 V, respectively. Furthermore, these catalyst candidates all have good stability and selectivity. Analyzing the band structures found that these catalyst candidates all are metallic, which is needed for good electrocatalysts. Ab initio molecular dynamics (AIMD) simulations show that these catalyst candidates have good stability at 500 K. It is hoped that our work will open up new possibilities for the experimental synthesis of electrochemical ammonia catalysts.

Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single-Atom Quantum Catalysts.

Regulating the catalytic pathways of single-atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single-atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single-atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen-rich functionalized carbon quantum dots (CQDs) matrix via a facile one-step and low-temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in-depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state-dependent catalytic pathways are employed for specific as well as cascade-like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.

Transition Metals Embedded Two-Dimensional Square Tetrafluorotetracyanoquinodimethane Monolayers as a Class of Novel Electrocatalysts for Nitrogen Reduction Reaction.

The combination of transition metal (TM) atoms and high electron affinity organic framework tetrafluorotetracyanoquinodimethanes (F4TCNQs) makes the TM-embedded two-dimensional (2D) square F4TCNQ monolayers (TM-sF4TCNQ) possible to have excellent characteristics of single-atom catalysts and 2D materials. For the first time, the TM-sF4TCNQ monolayers have been considered for application in the electrocatalytic nitrogen reduction reaction (eNRR) field. Through high-throughput screening, the catalytic performance of 30 TM-sF4TCNQ (TM = 3d∼5d TMs) monolayers for eNRR was comprehensively evaluated. The Mo-, Nb-, and Tc-sF4TCNQ catalysts stand out with the onset potentials of -0.18, -0.44, and -0.54 V, respectively, through the optimal reaction paths. Our work will provide guidance for the green and sustainable development of electrocatalytic nitrogen fixation.

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 (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.

Electrocatalytic Mechanism of N2 Reduction Reaction by Single-Atom Catalyst Rectangular TM-TCNQ Monolayers.

Herein, the catalytic properties and reaction mechanisms of the 3d, 4d, and 5d transition metals embedded in 2D rectangular tetracyanoquinodimethane (TM-rTCNQ) monolayers as single-atom catalysts (SACs) for the electrocatalytic N2 reduction reaction (NRR) were systematically investigated, using first-principles calculations. A series of high-throughput screenings were carried out on 30 TM-rTCNQ monolayers, and all possible NRR pathways were explored. Three TM-rTCNQ (TM = Mo, Tc, and W) SACs were selected as promising new NRR catalyst candidates because of their high structural stability and good catalytic performance (low onset potential and high selectivity). Our results show that the Mo-rTCNQ monolayer can catalyze NRR through a distal mechanism with an onset potential of -0.48 V. Surprisingly, the NH3 desorption energy on the Mo-rTCNQ monolayer is only 0.29 eV, the lowest one reported in the literature so far, which makes the Mo-rTCNQ monolayer a good NRR catalyst candidate. In-depth research studies on the structures of N2-TM-rTCNQ (TM = Mo, Tc, and W) found that strong adsorption and activation performance of TM-rTCNQ for N2 may be due to the strong charge transfer and orbital hybridization between the TM-rTCNQ catalyst and the N2 molecules. Our work provides new ideas for achieving N2 fixation under environmental conditions.