Single Transition Metal Atoms Research Articles

Regulating coordination environment around transition metal (Fe, Co) single atom catalysts for efficient Hg0 adsorption

Elemental mercury (Hg0) is one of the main pollutants released during coal combustion, which is difficult to remove due to its hydrophobicity and volatility, resulting in serious environmental pollution. Therefore, it is urgent to develop a low-cost and high-performance catalyst to remove Hg0. In this work, using first-principles study, the effect of nonmetal (NM = B, C and O) coordination environment on the charge distribution of graphene-supported transition metal single atom catalysts (TM-N4-SAC) has been investigated. It is found that regulating the TM-N4-SAC with NM coordination atoms with fewer valence electrons than N atom can cause TM atoms to lose more electrons, and the charge distribution in the active center to be locally deviated. Moreover, in-depth analysis of the adsorption configuration, charge density difference, charge transfer, adsorption energy and density of state of Hg0 adsorption on NM modified TM-N4-SAC confirmed that the adsorption of Hg0 can be effectively enhanced only when TM atoms lose more electrons. Thus, Fe-N3B- and Co-N3B-SAC have the strongest ability to adsorb Hg0 because they have the most negative adsorption energy of −1.13 and −0.49 eV. This work provides theoretical guidance for the design of SAC for efficient adsorption of Hg0.

Machine learning aided design of single-atom alloy catalysts for methane cracking

The process of CH4 cracking into H2 and carbon has gained wide attention for hydrogen production. However, traditional catalysis methods suffer rapid deactivation due to severe carbon deposition. In this study, we discover that effective CH4 cracking can be achieved at 450 °C over a Re/Ni single-atom alloy via ball milling. To explore single-atom alloy catalysis, we construct a library of 10,950 transition metal single-atom alloy surfaces and screen candidates based on C–H dissociation energy barriers predicted by a machine learning model. Experimental validation identifies Ir/Ni and Re/Ni as top performers. Notably, the non-noble metal Re/Ni achieves a hydrogen yield of 10.7 gH2 gcat–1 h–1 with 99.9% selectivity and 7.75% CH4 conversion at 450 °C, 1 atm. Here, we show the mechanical energy boosts CH4 conversion clearly and sustained CH4 cracking over 240 h is achieved, significantly surpassing other approaches in the literature.

Engineering Lewis-Acid Defects on ZnO Quantum Dots by Trace Transition-Metal Single Atoms for High Glycerol-to-Glycerol Carbonate Conversion.

Efficient conversion of biomass wastes into valuable chemicals has been regarded as a sustainable approach for green and circular economy. Herein, a highly efficient catalytic conversion of glycerol (Gly) into glycerol carbonate (GlyC) by carbonylation with the commercially available urea is presented using low-cost transition metal single atoms supported on zinc oxide quantum dots (M1-ZnO QDs) as a catalyst without using any solvent. A facile one-step wet chemical synthesis allows various types of metal single atoms to simultaneously dope and introduce Lewis-acid defects in the ZnO QD structure. It is found that doping with a trace amount of isolated metal atoms greatly boosts the catalytic activity with Gly conversion of 90.7%, GlyC selectivity of 100.0%, and GlyC yield of 90.6%. Congruential results from both Density Functional Theory (DFT)and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) studies reveal that the superior catalytic performance can be attributed to the enriched Lewis acid sites that endow optimal adsorption, formation of the intermediate for coupling between urea and Gly, and desorption of GlyC. Moreover, the tiny size of ZnO QDs efficiently promotes the accessibility of these active sites to the reactants.

Atomic-Level Asymmetric Tuning of the Co1-N3P1 Catalyst for Highly Efficient N-Alkylation of Amines with Alcohols.

Despite the extensive development of non-noble metals for the N-alkylation of amines with alcohols, the exploitation of catalysts with high selectivity, activity, and stability still faces challenges. The controllable modification of single-atom sites through asymmetric coordination with a second heteroatom offers new opportunities for enhancing the intrinsic activity of transition metal single-atom catalysts. Here, we prepared the asymmetric N/P hybrid coordination of single-atom Co1-N3P1 by absorbing the Co-P complex on ZIF-8 using a concise impregnation-pyrolysis process. The catalyst exhibits ultrahigh activity and selectivity in the N-alkylation of aniline and benzyl alcohol, achieving a turnover number (TON) value of 3480 and a turnover frequency (TOF) value of 174-h. The TON value is 1 order of magnitude higher than the reported catalysts and even 37-fold higher than that of the homogeneous catalyst CoCl2(PPh3)2. Furthermore, the catalyst maintains its high activity and selectivity even after 6 cycles of usage. Controlling experiments and isotope labeling experiments confirm that in the asymmetric Co1-N3P1 system, the N-alkylation of aniline with benzyl alcohol proceeds via a transfer hydrogenation mechanism involving the monohydride route. Theoretical calculations prove that the superior activity of asymmetric Co1-N3P1 is attributed to the higher d-band energy level of Co sites, which leads to a more stable four-membered ring transition state and a lower reaction energy barrier compared to symmetrical Co1-N4.

Dual-Atom P-Co-Dy Charge-Transfer Bridge on Black Phosphorus for Enhanced Photocatalytic CO2 Reduction.

The synergistic effect of rare earth single-atoms and transition metal single-atoms may enable us to achieve some unprecedented performance and characteristics. Here, Co-Dy dual-atoms on black phosphorus with a P-Co-Dy charge-transfer bridge are designed and fabricated as the active center for the CO2 photoreduction reaction. The synergistic effect of Co-Dy on the performance of black phosphorus is studied by combining X-ray absorption spectroscopy, ultrafast spectral analysis, and in situ technology with DFT calculations. The results show that the Co and Dy bimetallic active site can promote charge transfer by the charge transfer bridge from P to Dy, and then to Co, thereby improving the photocatalytic activity of black phosphorus. The performance of catalysts excited at different wavelength light indicates that the 4G11/2/2I15/2/4F9/2→6H15/2 and 4F9/2→6H13/2 emissions of Dy can be absorbed by black phosphorus to improve the utilization of sunlight. The in situ DRIFTS and density functional theory (DFT) calculations are used to investigate the CO2 photoreduction pathway. This work provides an depth insight into the mechanism of dual-atom catalysts with enhanced photocatalytic performance, which helps to design novel atomic photocatalysts with excellent activity for CO2 reduction reactions.

Sp/sp2 carbon ratio-driven high-throughput screening of electrocatalytic nitrogen reduction performance on transition metal single-atom catalysts

Sp/sp2 carbon ratio-driven high-throughput screening of electrocatalytic nitrogen reduction performance on transition metal single-atom catalysts

Theoretical investigation on gas sensing characteristics of 3d transition metal atom doped C9N7 for toxic gases (CO, NO, NO2, and SO2)

This study investigates the sensing performance of a series of 3d transition metal doped C9N7 sensor structures for four toxic gases (CO, NO, NO2, and SO2). A series of sensor configurations with single and double 3d transition metal atoms doped with C9N7 (TM-C9N7 and TM2-C9N7) are constructed. The stability of the sensor configuration is evaluated by calculating the formation energy and dissolution potential. The stability analysis results indicate that except Sc-C9N7, Mn2-C9N7, and Cr2-C9N7, all sensor configurations have good structural stability. For screened sensor structures with good structural stability, the adsorption energy values of four toxic gases and three common gases (N2, O2, and CO2) are compared to evaluate their selectivity towards toxic gases. Moreover, the recovery times are also calculated to further evaluate the sensing performance. Through comprehensive evaluation, four sensor structures (Fe-C9N7, Cu-C9N7, Zn-C9N7, and Zn2-C9N7) with high selectivity and relatively short recovery time for toxic gases are determined. Among them, Fe-C9N7 is suitable for sensors of toxic gases NO2, and SO2, while Cu-C9N7, Zn-C9N7, and Zn2-C9N7 have good sensing performance for all four toxic gases.

Transition metal single-atom supported on W2N3 as efficient electrocatalysts for the nitrogen reduction reaction: A DFT study

The problems of poor Faraday efficiency and high overpotential usually limit electrochemical nitrogen reduction (NRR) catalysts. In this paper, 28 different transition metal single-atoms (TM-SAs) supported on W2N3 (TM@W2N3) were designed by density functional theory (DFT) for catalytic N2 reduction. The stability, N2 activation capacity, selectivity and NRR mechanism of TM@W2N3 were analyzed. Following the screening process, only 9 TM@W2N3 (TM=Sc, Ti, V, Co, Cu, Y, Mo, Ag, W) structures were identified as exhibiting high stability, strong activation capacity and high NRR selectivity. And then N2 activation mechanism of V@W2N3, Mo@W2N3 and W@W2N3, as well as the Gibbs free energies of its four NRR reaction pathways were further discussed. The overpotentials (η) of Mo@W2N3 and V@W2N3 to NRR are 0.129 V and 0.470 V, respectively. The overpotential (η) of W@W2N3 is the lowest at 0.059 V, while its catalytic activity is the highest. V@W2N3 and W@W2N3 are more likely to follow the distal pathway for NRR, while Mo@W2N3 is more likely to follow the enzymatic pathway. This study offers some theoretical foundation and reference for the design of new and efficient electrocatalytic NRR catalysts.

Single‐Atom Catalysts Based on the Mo2CO2 MXene for CO Oxidation

AbstractThrough density functional theory calculations, the mechanism of CO oxidation to CO2 on single‐atom catalysts consisting of an atom of Ti, Fe, or Zn deposited on the surface of the Mo2CO2 MXene is investigated. In the case of Fe@Mo2CO2, a mechanism resembling that of Termolecular Langmuir–Hinshelwood (TLH) is thermodynamically and kinetically favored, displaying very exothermic CO2 formation, low activation energies, and easy CO2 desorption. On Ti@Mo2CO2, the dissociation of CO2 is almost barrierless and much more likely to occur than CO2 desorption, barring the usage of this surface as a catalyst for CO oxidation. Finally, on Zn@Mo2CO2, a hybrid Langmuir–Hinshelwood/Eley–Rideal (LH/ER) mechanism is thermodynamically and kinetically feasible. Here, after the first CO2 forms, with an energy barrier of only 0.62 eV, the second CO2 is formed spontaneously, and the Zn–CO2 interactions are weak enough to allow desorption. The calculated thermodynamic quantities and reaction rates at T = 300 K indicate that Fe@Mo2CO2 should be quite active toward CO oxidation, followed by Zn@Mo2CO2, while the Ti‐based model is inactive. The results add to the evidence that establishes single transition metal atoms adsorbed on MXene surfaces as cheap and easily obtainable catalysts that offer the best of both bare and functionalized MXenes.

Polyoxometalate Supported Single Transition Metal Atom as a Redox Mediator for Li-O2 Batteries.

Keggin-type polyoxometalate (POM) supported single transition metal (TM) atom (TM1/POM) as an efficient soluble redox mediator for Li-O2 batteries is comprehensively investigated by first-principles calculations. Among the pristine POM and four kinds of TM1/POM (TM = Fe, Co, Ni, and Pt), Co1/POM not only maintains good structural and thermodynamic stability in oxidized and reduced states but also exhibits promising electro(chemical) catalytic performance for both oxygen reduction reaction and oxygen evolution reaction (OER) in Li-O2 batteries with the lowest Gibbs free energy barriers. Further investigations demonstrate that the moderate binding strength of Li2-xO2 (x = 0, 1, and 2) intermediates on Co1/POM guarantees favorable Li2O2 formation and decomposition. Electronic structure analyses indicate that the introduced Co single atom as an electron transfer bridge can not only efficiently improve the electronic conductivity of POM but also regulate the bonding/antibonding states around the Fermi level of [Co1/POM-Li2O2]ox. The solvent effect on the OER catalytic performance and the electronic properties of [Co1/POM-Li2O2]ox with and without dimethyl sulfoxide solvent are also investigated.

Rare-metal-free hydrogen evolution reaction electrocatalysts based on metal azaphthalocyanine molecular layer for anion exchange membrane water electrolysis

In this report, we elucidated the hydrogen evolution reaction (HER) catalytic activity of different metal-azaphthalocyanine unimolecular layer (AZUL) catalysts and compared the overpotentials in alkaline electrolyte membrane water electrolysis (AEMWE). While the overpotentials are bit higher compared to Pt/C, the system utilizing the FeAzPc-4N with Sustainion® showed a low overpotential of 2.02 V at 1.0 A/cm2 and faraday efficiency of 96.3% even among the previous alternative catalysts. It is noteworthy that the AZUL catalysts are not using precious metals and even comparing with other transition metal electrocatalysts, metal atom usage is much lower because only the single transition metal atom in the azapthalocyanine macrocycle works as a catalytic site.

Two-dimensional MXene supported single transition metal atom for HCHO catalytic oxidation: A first-principles study combined with Microkinetics

Catalytic oxidation is an efficient and environmentally friendly strategy for the removal of pollutant HCHO. Recent proof-of-concepts experiments indicate that single-atom catalysts (SACs) exhibit good activity for HCHO catalytic degradation, but a major obstacle is to look for an effective SAC. Herein, ten 3d transition metal SACs decorated on Mo2CS2 substrate were designed and constructed to catalyze HCHO using periodic density functional theory calculations. The results showed that the single atoms are inclined to locate at the Mo top site on the surface and most SACs can stay stable. Among these SCAs, Ti, V, Cr, and Mn SACs have shallow energy barriers of O2 activation and can facilitate O2 dissociation at room temperature. Therefore, two typical HCHO oxidation pathways on TM@Mo2CS2 (TM = Ti, V, Cr, and Mn) catalyst were investigated in detail. The V@Mo2CS2 has the lowest energy barrier of 1.72 eV for the rate-limiting step during HCHO oxidation via path-Ⅰ (O2 adsorption and activation, HCHO* → CHO* → CO* → CO2*). Correlation analysis verifies that the Bader charge and O2 adsorption are the appropriate descriptions for HCHO catalytic oxidation activity. Microkinetic simulations are further performed to reveal the relationship between HCHO oxidation rate and temperature.

Enhanced photocatalytic hydrogen generation efficiency through molybdenum-sulfur dual sites synergistic catalysis

Photocatalysis has gained significant attention in recent years for water splitting, with graphitic carbon nitride (g-C3N4) emerging as a promising candidate. However, the low carrier mobility and the lack of active sites for hydrogen evolution limit photocatalytic hydrogen evolution performance. Herein, this work presents a facile approach to achieve single Mo sites with a unique local coordination structure featuring one Mo atom coordinated with two nitrogen atoms and one sulfur atom. Among the prepared photocatalysts, 6 wt% Mo/SCN exhibits the highest photocatalytic hydrogen evolution activity with a yield rate of 4.05 mmol g-1 h-1, which is 13 times higher than that of pure g-C3N4 and superior to most of the g-C3N4 series photocatalysts. Experimental results and density functional theory calculations confirm that the Mo single-atom and S atom have synergistic catalysis under the co-modification, and the formed Mo-S bonds will enhance the ability of the substrate to anchor the Mo single-atom to enhance the stability of the photocatalyst. This work offers insights into transition metal single-atom and synergistic catalysis design for photocatalytic hydrogen evolution.

Mechanistic Diversity in the Hydrolysis of Sarin by Single Transition-Metal Atoms on MOF-808

Mechanistic Diversity in the Hydrolysis of Sarin by Single Transition-Metal Atoms on MOF-808

Single Transition Metal Atom Catalyst for a High-Performance Li–S Battery with a Graphdiyne–Graphene Heterostructure Host: A DFT Investigation + ML Predictions

Single Transition Metal Atom Catalyst for a High-Performance Li–S Battery with a Graphdiyne–Graphene Heterostructure Host: A DFT Investigation + ML Predictions

Main Group SnN4O Single Sites with Optimized Charge Distribution for Boosting the Oxygen Reduction Reaction.

Transition metal single-atom catalysts (SACs) have been regarded as possible alternatives to platinum-based materials due to their satisfactory performance of the oxygen reduction reaction (ORR). By contrast, main-group metal elements are rarely studied due to their unfavorable surface and electronic states. Herein, a main-group Sn-based SAC with penta-coordinated and asymmetric first-shell ligands is reported as an efficient and robust ORR catalyst. The introduction of the vertical oxygen atom breaks the symmetric charge balance, modulating the binding strength to oxygen intermediates and decreasing the energy barrier for the ORR process. As expected, the prepared Sn SAC exhibits outstanding ORR activity with a high half-wave potential of 0.912 V (vs RHE) and an excellent mass activity of 13.1 A mgSn-1 at 0.850 V (vs RHE), which surpasses that of commercial Pt/C and most reported transition-metal-based SACs. Additionally, the reported Sn SAC shows excellent ORR stability due to the strong interaction between Sn sites and the carbon support with oxygen atom as the bridge. The excellent ORR performance of Sn SAC was also proven by both liquid- and solid-state zinc-air battery (ZAB) measurements, indicating its great potential in practical applications.

Insight of hydrogen evolution reaction in slab SnO2 loaded with transition metal atoms

The utilization of hydrogen energy has emerged as a promising solution for clean and sustainable energy sources. The development of cost-effective catalysts with high activity and stability is crucial for efficient hydrogen production. In this work, we investigated the hydrogen evolution reaction (HER) catalytic activity of single transition metal atom (TM = V, Cr, Mn, Fe, Co, Ni) on slab SnO2 by using density functional theory. Our results revealed that the catalytic activity of the slab SnO2 can be significantly enhanced by loading the transition atom. By calculating the Gibbs free energies and exchange current densities in different adsorption configurations of TM-SnO2, single-atom catalyst (SAC) of Mn-loaded SAC exhibits excellent catalytic performance, characterized by a low Gibbs free energy barrier (−0.05 eV). Introducing a TM on the SnO2 surface breaks its local symmetry, while the strong coupling between the metal and H atoms enhances catalytic performance. The synergetic effect of symmetry breaking and metal-H interaction boosts overall catalytic activity. This work not only proposes a novel non-platinum HER catalyst based on SnO2 but also lays a solid foundation for future applications of SnO2-based catalysts.

Fully exposed copper single-atom sites on mesoporous N/S-codoped graphene for efficient zinc-air battery

Transition metal single-atom catalysts are recently emerging as the most potential candidates for the oxygen reduction reaction due to their remarkable activity and durability, yet subjected to limited availability proportion of active sites to reactant in practice due to the lack of favorable morphology. Herein, the ultrathin mesoporous N/S-codoped graphene is fabricated by a potassium thiocyanate (KSCN) assisted pyrolysis of metal-organic framework (ZIF-8) as the robust substrate for anchoring copper single-atom sites. The KSCN-assisted pyrolysis can not only create N and S coordination atoms but also regulate the fully exposed morphology. The graphene-supported copper single-atom catalysts (g-Cu-SACs) show typical mesoporous structure with larger surface area of 1612 m2 g–1. Spectral and microscopy results reveal highly isolated Cu single-atom sites on mesoporous graphene with unsymmetrical Cu-S1N3 structure. Theoretical analysis demonstrated that the asymmetric coordination environment effectively enhanced O2 adsorption and facilitated the ORR performance. The g-Cu-SACs show excellent catalytic activity in alkaline oxygen reduction reaction with a half-wave potential of 0.920 VRHE and good cycling stability, which are superior to that of three-dimensional copper single-atom catalysts (Cu-SACs, supported by N/S-codoped carbon framework directly derived from ZIF-8). Furthermore, the zinc-air battery assembled with g-Cu-SACs also exhibits high specific capacity and remarkable cycling lifetime. This work provides a novel strategy to construct highly exposed single-atom catalysts for energy-related applications.

Constructing Single-Atom Active Sites Embedded in Hexagonal Boron Nitride for Adsorption and Sensing of Lithium Battery Thermal Runaway Gases.

The utilization and selectivity of single atoms have garnered significant attention among researchers. However, they are easy to agglomerate because of their high surface energy. To overcome this challenge, it is crucial to seek suitable carriers to anchor single metal atoms to achieve optimal performance. In this work, the structures of transition metal single atoms embedded in hexagonal boron nitride (MB2N2, M = Fe, Co, Ni, Cu, Zn) are constructed and used for the adsorption and sensing of lithium battery thermal runaway gases (H2, CO, CO2, CH4) through the DFT method. The adsorption behavior of MB2N2 was evaluated through the adsorption energy, sensitivity, and recovery time. The calculation results indicate that CoB2N2 exhibits strong adsorption capacity for both H2 and CO. The sensitivity of FeB2N2 toward CO is as high as 3.232 × 1016. Subsequently, the adsorption mechanism was studied through TDOS and PDOS, and the results showed that hybridization between orbitals enhanced the gas adsorption performance. This study presents novel approaches for designing single-atom carriers and developing MB2N2 sensors for detecting lithium battery thermal runaway gases.

Single transition-metal atoms anchored on a novel Dirac-dispersive π-π conjugated holey graphitic carbon nitride substrate: computational screening toward efficient bifunctional OER/ORR electrocatalysts

Single transition-metal atoms anchored on a novel Dirac-dispersive π-π conjugated holey graphitic carbon nitride substrate: computational screening toward efficient bifunctional OER/ORR electrocatalysts