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.

Establishing Transition Metal Phosphides as Effective Sulfur Hosts in Lithium-Sulfur Batteries through the Triple Effect of "Confinement-Adsorption-Catalysis".

Structurally optimized transition metal phosphides are identified as a promising avenue for the commercialization of lithium-sulfur (Li-S) batteries. In this study, a CoP nanoparticle-doped hollow ordered mesoporous carbon sphere (CoP-OMCS) is developed as a S host with a "Confinement-Adsorption-Catalysis" triple effect for Li-S batteries. The Li-S batteries with CoP-OMCS/S cathode demonstrate excellent performance, delivering a discharge capacity of 1148 mAh g-1 at 0.5 C and good cycling stability with a low long-cycle capacity decay rate of 0.059% per cycle. Even at a high current density of 2 C after 200 cycles, a high specific discharge capacity of 524 mAh g-1 is maintained. Moreover, a reversible areal capacity of 6.56 mAh cm-2 is achieved after 100 cycles at 0.2 C, despite a high S loading of 6.8 mg cm-2 . Density functional theory (DFT) calculations show that CoP exhibits enhanced adsorption capacity for sulfur-containing substances. Additionally, the optimized electronic structure of CoP significantly reduces the energy barrier during the conversion of Li2 S4 (L) to Li2 S2 (S). In summary, this work provides a promising approach to optimize transition metal phosphide materials structurally and design cathodes for Li-S batteries.

Low-Coordinated Pd Site within Amorphous Palladium Selenide for Active, Selective, and Stable H2 O2 Electrosynthesis.

The development of high-performance catalysts with high activity, selectivity, and stability are essential for the practical applications of H2 O2 electrosynthesis technology, but it is still formidably challenging. It is reported that the low-coordinated structure of Pd sites in amorphous PdSe2 nanoparticles (a-PdSe2 NPs) can significantly boost the electrocatalytic synthesis of H2 O2 . Detailed investigations and theoretical calculations reveal that the disordered arrangement of Pd atoms in a-PdSe2 NPs can promote the activity, while the Pd sites with low-coordinated environment can optimize the adsorption toward oxygenated intermediate and suppress the cleavage of O-O bond, leading to a significant enhancement in both the H2 O2 selectivity and productivity. Impressively, a-PdSe2 NPs/C exhibits high H2 O2 selectivity over 90% in different pH electrolytes. H2 O2 productivities with ≈3245.7, 1725.5, and 2242.1 mmol gPd -1  h-1 in 0.1 m KOH, 0.1 m HClO4 , and 0.1 m Na2 SO4 can be achieved, respectively, in an H-cell electrolyzer, being a pH-universal catalyst for H2 O2 electrochemical synthesis. Furthermore, the produced H2 O2 can reach 1081.8 ppm in a three-phase flow cell reactor after 2 h enrichment in 0.1 m Na2 SO4 , showing the great potential of a-PdSe2 NPs/C for practical H2 O2 electrosynthesis.

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.