Metal Atoms Research Articles

Catalysts with Trimetallic Sites on Graphene-like C2N for Electrocatalytic Nitrogen Reduction Reaction: A Theoretical Investigation.

Electrocatalytic nitrogen reduction reaction (NRR) is a green and highly efficient way to replace the industrial Haber-Bosch process. Herein, clusters consisting of three transition metal atoms loaded on C2N as NRR electrocatalysts are investigated using density functional theory (DFT). Meanwhile, Ca was introduced as a promoter and the role of Ca in NRR was investigated. It was found that Ca anchored to the catalyst can act as an electron donor and effectively promote the activation of N2 on M3. In both M3@C2N and M3Ca@C2N (M=Fe, Co, Ni), the limiting potential (UL) is less negative than that of the Ru(0001) surface and has the ability to suppress the competitive hydrogen evolution reaction (HER). Among them, Fe3@C2N is suggested to be the most promising candidate for NRR with high thermal stability, strong N2 adsorption ability, low limiting potential, and good NRR selectivity. The concepts of trimetallic sites and alkaline earth metal promoters in this work provide theoretical guidance for the rational design of atomically active sites in electrocatalytic NRR.

Atomic-level Engineered Cobalt Catalysts for Fenton-Like Reactions: Synergy of Single Atom Metal Sites and Nonmetal-bonded Functionalities.

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of co-existing non-TM-bonded functionalities are usually overlooked in catalysis. Herein, we reported the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co-N sites and free functional N species. We first systematically study the role of metal and nonmetal bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co-N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the non-metal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10min with an ultrahigh turnover frequency of 0.38min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems. This article is protected by copyright. All rights reserved.

Potential of Molecular Catalysts with Electron-Rich Transition Metal Centers for Addressing Long-Standing Chemistry Enigmas.

Molecular complexes with electron-rich metal centers are highlighted as potential catalysts for the following five important chemical transformations: selective conversion of methane to methanol, capture and utilization of carbon dioxide, fixation of molecular nitrogen, water splitting, and recycling of perfluorochemicals. Our initial focus lies on negatively charged metal centers and ligands that can stabilize anionic metal atoms. Catalysts with electron-rich metal atoms (CERMAs) can sustain catalytic cycles with a "ping-pong" mechanism, where one or more electrons are transferred from the metal center to the substrate and back. The donated electrons can activate the chemical bonds of the substrate by populating its antibonding orbitals. At the last step of the catalytic cycle, the electrons return to the metal and the product interacts only weakly with the formed anion, which enables the solvent molecules to remove the product fast from the catalytic cycle and prevent subsequent unfavorable reactions. This process resembles electrocatalysis, but the metal serves as both an anode and a cathode (molecular electrocatalysis). We also analyze the usage of CERMAs as the base of Frustrated Lewis pairs proposing a new type of bimetallic catalysts. This Featured Article aspires to initiate systematic experimental and theoretical studies on CERMAs and their reactivity, the potential of which has probably been underestimated in the literature.

Design of Single-atom Catalysts on C5N2 forNitrogen Fixation at Ambient Conditions : A First-principles Study.

Single atom catalysts (SACs) exhibit the flexible coordinationstructure of the active site and high utilization of activeatoms, making them promising candidates for nitrogenreduction reaction (NRR) under ambient conditions. Bythe aid of first-principles calculations based on DFT, wehavesystematically explored the NRR catalytic behavior ofthirteen 4d- and 5d-transition metal atoms anchored on 2Dporous graphite carbon nitride C5N2. With high selectivityand outstanding activity, Zr, Nb, Mo, Ta, W and Re-dopedC5N2 are identified as potential nominees for NRR. Particularly,Mo@C5N2 possesses an impressive low limiting potentialof -0.39 V (corresponding to a very low temperatureand atmospheric pressure), featuring the potential determiningstep involving *N-N transitions to *N-NH via thedistal path. The catalytic performance of TM@C5N2 canbe well characterized by the adsorption strength of intermediate*N2H. Moreover, there exists a volcanic relationshipbetween the catalytic property UL and the structure descriptorΨ, which validates the robustness and universalityof Ψ, combined with our previous study. This work sheds light on the design of SACs with eminent NRR performance.

Precision engineering of nano-assemblies in superfluid helium by the use of van der Waals forces

The ability to precisely engineer nanostructures underpins a wide range of applications in areas such as electronics, optics, and biomedical sciences. Here we present a novel approach for the growth of nanoparticle assemblies that leverages the unique properties of superfluid helium. Unlike viscous solvents at or near room temperature, superfluid helium provides an unperturbed and cold environment in which weak van der Waals interactions between molecular templates and metal atoms become significant and can define the spatial arrangement of nanoparticles. To demonstrate this concept, diol and porphyrin-based molecules are employed as templates to grow gold nanoparticle assemblies in superfluid helium droplets. After soft-landing on a solid surface to remove the helium, transmission electron microscopy (TEM) imaging shows the growth of gold nanoparticles at specific binding sites within the molecular templates where the interaction between gold atoms and the molecular template is at its strongest.

Single atoms and metal nanoclusters anchored to graphene vacancies

Fabricating dispersed single atoms and size-controlled metal nanoclusters remains a difficult challenge due to sintering. Here, we demonstrate that atoms and clusters can be immobilized using atomically clean defect-engineered graphene as the matrix. The graphene is first cleaned of surface contamination with laser heating, after which low-energy Ar irradiation is used to create spatially well-separated vacancies into it. Metal atoms are then evaporated either via thermal or ebeam evaporation onto graphene, where they diffuse until being trapped into a vacancy. The density of embedded structures can be controlled through irradiation dose, and the size of the structures through evaporation time. The resulting structures are confirmed through atomic-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. We demonstrate here incorporation of Al, Ti, Fe, Ag and Au single atoms or nanoclusters, but the method should work equally well for other elements.

Unveiling Highly Sensitive Active Site in Atomically Dispersed Gold Catalysts for Enhanced Ethanol Dehydrogenation

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the “complex active site” consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The “complex active site” Au‐Vo‐Zr3+ on Au1/ZrO2 exhibits the highest H2 production rate, with above 37,964 mol H2 per mol Au per hour (385 g H2 g‐1 Au h‐1) at 350 oC, which is 3.32, 2.94 and 15 times higher than Au1/CeO2, Au1/TiO2, and Au1/Al2O3, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost‐effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic‐level catalyst design by colocalizing catalytically active metal atoms forming a structure‐sensitive “complex site”, is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Interaction of C, N and O interstitial solute atoms with screw dislocations in HfNbTaTiZr high entropy alloy

Using density functional theory (DFT), we characterize the interaction of screw dislocations with interstitial impurities, in particular oxygen, nitrogen and carbon, in the HfNbTaTiZr alloy of body-centered cubic (BCC) structure. Considering different configurations representative of the disordered solid solution alloy, we evidence a noticeable core spreading of the screw dislocation whether with or without solute, associated with a wide range in dislocation-solute interaction energy, which is found to be mainly attractive for the three investigated impurities. This interaction energy is shown to be highly influenced by the type of the metal atoms in the neighbourhood of the solute. Notably the more BCC elements are present around the solute (either Nb or Ta), the more repulsive this interaction is.

Unveiling Highly Sensitive Active Site in Atomically Dispersed Gold Catalysts for Enhanced Ethanol Dehydrogenation.

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the "complex active site" consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The "complex active site" Au-Vo-Zr3+ on Au1/ZrO2 exhibits the highest H2 production rate, with above 37,964 mol H2 per mol Au per hour (385 g H2 g-1 Au h-1) at 350 oC, which is 3.32, 2.94 and 15 times higher than Au1/CeO2, Au1/TiO2, and Au1/Al2O3, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost-effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic-level catalyst design by colocalizing catalytically active metal atoms forming a structure-sensitive "complex site", is a crucial way to advance from heterogeneous catalysis to molecular catalysis.Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

Dual surface defects induced efficient interfacial electron transfer in S-scheme hollow ZnO@ZnS heterojunction for uranium (VI) removal

Photocatalytic reduction is a promising way to remove radioactive uranium U(VI) in wastewater. Herein, an S-scheme ZnO@ZnS heterojunction with hollow structure and dual-vacancies of Zn and S (ZnV, SV) is developed. The hollow confined space enhances light trapping ability through multiple light scattering and reflection, while the existence of vacancies extends light absorption, further enhancing the utilization of solar spectrum. Furthermore, the density function theory (DFT) calculations demonstrate that co-sharing of metal atoms at the interface and the ZnV and SV dual-vacancies induce enhanced internal electric field (IEF), leading to facilitated S-scheme charge transfer, thereby resulting in improved retention of redox potential and suppressed carrier recombination dynamics. ZnO@ZnS shows a highest U(VI) removal rate of 96.48% along with a highest U enrichment of 514.33 mg/g, which is 3.6 and 2.7-folds enhanced compared to pristine ZnO and ZnS, respectively. Through various quenching experiments, a potential new mechanism for the catalytic reduction of U(VI) is proposed. Our findings reveal the involvement of h+ in the reaction, highlighting its significant catalytic role in the reduction process. Moreover, ZnO@ZnS performs excellent U(VI) extraction ability in open-air conditions without any sacrificial agents, revealing the great significance for practical applications.

On working gas rarefaction in high power impulse magnetron sputtering

The ionization region model (IRM) is applied to explore working gas rarefaction in high power impulse magnetron sputtering discharges operated with graphite, aluminum, copper, titanium, zirconium, and tungsten targets. For all cases the working gas rarefaction is found to be significant, the degree of working gas rarefaction reaches values of up to 83%. The various contributions to working gas rarefaction, including electron impact ionization, kick-out by the sputtered species or hot argon atoms, and diffusion, are evaluated and compared for the different target materials, and over a range of discharge current densities. The relative importance of the various processes varies between different target materials. In the case of a graphite target with argon as the working gas at 1 Pa, electron impact ionization (by both primary and secondary electrons) is the dominating contributor to working gas rarefaction, with over 90% contribution, while the contribution of sputter wind kick-out is small <10 %. In the case of copper and tungsten targets, the kick-out dominates, with up to ∼60% contribution at 1 Pa. For metallic targets the kick-out is mainly due to metal atoms sputtered from the target, while for the graphite target the small kick-out contribution is mainly due to kick-out by hot argon atoms and to a smaller extent by carbon atoms. The main factors determining the relative contribution of the kick-out by the sputtered species to working gas rarefaction appear to be the sputter yield and the working gas pressure.

Mechanistic study of moisture corrosion of FeCr alloys in molten salts by ab-initio molecular dynamics simulations

Molten salts are promising for various energy applications including fuel and solar cells and nuclear energy. These applications face a common challenge: corrosion of structural materials by impurities such as H2O. This work employs ab-initio molecular dynamics simulations to study H2O induced corrosion of FeCr alloys in molten NaF and NaCl salts. H2O is found highly stable in both salts, with infrequent, reversible dissociation into OH− and H+ along with HF or HCl formation. The dissociation tendency correlates positively with the electronegativity and negatively with the size of halogen atoms. Accordingly, H2O reaches the salt/metal interface as a molecule before reacting with metal. Reduction of H+ is found to occur without simultaneous oxidation of specific metal atoms such as Cr, suggesting sequential instead of the commonly proposed concurrent reduction and oxidation. The reduced H atoms prefer to stay at the interface and may re-enter NaF but not NaCl, highlighting the influence of salt chemistry.

Transition metal ions doped into Haeckelite-MoS2 as highly efficient and selective electrocatalyst for nitrogen reduction reaction

Due to the high-cost energy and environmental damage of industrial ammonia production, utilizing the catalyst to improve the reaction efficiencies has been regarded as a potential way. In this work, the electrocatalytic nitrogen reduction reaction (NRR) of a series of transition metal atoms (TMs: 3d, 4d and 5d atoms) doped Haeckelite-MoS2 nanosheet (TM@HL-MoS2) is systematically investigated by using density function theory (DFT) calculations. Comparing with the HL-MoS2, the role of TM doping is highlighted by the partial density of status (PDOS) and the charge variations, which can provide an active site for NRR and serve as an intermediate for electron transfer from HL-MoS2 to adsorbed molecule. After evaluating the activation of N2 and the Gibbs free energy, the best catalyst can be found in the three possible NRR paths. Meanwhile, the further application of TM@HL-MoS2 is tested by the thermodynamic stability and the competitiveness with hydrogen evolution reactions.

Regulated reaction pathway of CO2 photoreduction into CH4 by metal atom pair sites

Regulated reaction pathway of CO2 photoreduction into CH4 by metal atom pair sites

Synthesis, characterization, crystal structures and biological activity of novel NiII2ZnII2 complexes derived from 2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol

Molecular nanoclusters comprising heterometallic Ni-Zn cores are an interesting class of compounds. In this paper, five novel NiII-ZnII complexes [Ni2Zn2ClL3(HL)3]·0·.25H2O (1), [Ni2Zn2BrL3(HL)3]·0·.25H2O (2), [Ni2Zn2Br2L2(N3)2(MeOH)2]·2MeOH (3), [Ni2Zn2I2L2(N3)2(MeOH)2]·2MeOH (4), and [Ni2Zn2I2L2(N3)2(DMF)2] (5), were prepared from the Schiff base 2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol (H2L). The complexes have been characterized by elemental analysis, IR, UV–Vis spectra. Molecular structures of the complexes have been determined by single crystal X-ray determination. In complexes 1 and 2, three of the Schiff bases coordinate to the metal atoms via ether oxygen, imino nitrogen and two phenolate oxygen atoms, while the fourth one coordinates through ether oxygen, imino nitrogen and one phenolate oxygen atoms. In complexes 3, 4 and 5, all the donor atoms in the Schiff base ligands participate in coordination. The Ni and Zn atoms in the complexes are in octahedral and trigonal bipyramidal coordination, respectively. The anions of the metal salts and the azide anion, as well as methanol and DMF molecules furnish the coordination sphere. The compounds were evaluated for their antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens, and antifungal activities on Candida albicans and Aspergillus niger. Interestingly, the complexes have effective activities against Bacillus subtilis and Staphylococcus aureus.

Theoretical study of the CO2 activation on modified MoS2/CsPbBr3 photocatalysts

Photocatalytic CO2 reduction emerges as a promising strategy to mitigate global warming and energy crises. The MoS2/CsPbBr3 complexes, recognized as the groundbreaking and efficient photocatalysts, have drawn considerable attention for their CO2 reduction capabilities. In this work, we conducted an extensive analysis of the CO2 activation on the various MoS2/CsPbBr3 surfaces, including perfect MoS2/CsPbBr3, M@MoS2/CsPbBr3 (single metal atom loading), defect-MoS2/CsPbBr3 (including VS, VMo, V2S, MoS, SMo and VMoS3), and VS−M@MoS2/CsPbBr3 (single metal atom doping VS site). Our investigation encompassed the geometric and electronic structures of these systems and their interactions with CO2 molecules, particularly the role of surface termination in above processes. The findings indicate that MoS2/CsPbBr3 systems, whether loading with single metal atoms or containing defects, show a significantly enhanced ability to activate CO2. Conversely, perfect MoS2/CsPbBr3 and VS−M@MoS2/CsPbBr3 demonstrate only a moderate capacity for CO2 activation. It is crucial that the activation of CO2 depends on whether the above modification methods introduce gap states between the VBM and CBM. Meanwhile, we find that the adsorption of CO2 on the surfaces of MoS2/CsPbBr3 loaded with single metal atoms and doped with them is significantly influenced by the terminals. While the terminals do not significantly affect the CO2 adsorption on MoS2/CsPbBr3 with defects. Furthermore, based on the CO2 activation models, we further investigate the Gibbs free energy change of the reaction pathway for CO2 photocatalytic reduction to CO. Through our research, we aim to provide useful theoretical insights for the design and preparation of novel CO2 reduction photocatalysts.

High-Entropy Alloy Electrocatalysts Bidirectionally Promote Lithium Polysulfide Conversions for Long-Cycle-Life Lithium-Sulfur Batteries.

High-entropy alloys (HEAs) have attracted considerable attention, owing to their exceptional characteristics and high configurational entropy. Recent findings demonstrated that incorporating HEAs into sulfur cathodes can alleviate the shuttling effect of lithium polysulfides (LiPSs) and accelerate their redox reactions. Herein, we synthesized nano Pt0.25Cu0.25Fe0.15Co0.15Ni0.2 HEAs on hollow carbons (HCs; denoted as HEA/HC) by a facile pyrolysis strategy. The HEA/HC nanostructures were further integrated into hypha carbon nanobelts (HCNBs). The solid-solution phase formed by the uniform mixture of the five metal elements, i.e., Pt0.25Cu0.25Fe0.15Co0.15Ni0.2 HEAs, gave rise to a strong interaction between neighboring atoms in different metals, resulting in their adsorption energy transformation across a wide, multipeak, and nearly continuous spectrum. Meanwhile, the HEAs exhibited numerous active sites on their surface, which is beneficial to catalyzing the cascade conversion of LiPSs. Combining density functional theory (DFT) calculations with detailed experimental investigations, the prepared HEAs bidirectionally catalyze the cascade reactions of LiPSs and boost their conversion reaction rates. S/HEA@HC/HCNB cathodes achieved a low 0.034% decay rate for 2000 cycles at 1.0 C. Notably, the S/HEA@HC/HCNB cathode delivered a high initial areal capacity of 10.2 mAh cm-2 with a sulfur loading of 9 mg cm-2 at 0.1 C. The assembled pouch cell exhibited a capacity of 1077.9 mAh g-1 at the first discharge at 0.1 C. The capacity declined to 71.3% after 43 cycles at 0.1 C. In this work, we propose to utilize HEAs as catalysts not only to improve the cycling stability of lithium-sulfur batteries, but also to promote HEAs in energy storage applications.

Inhibiting Demetalation of Fe-N-C via Mn Sites for Efficient Oxygen Reduction Reaction in Zinc-Air Batteries.

Demetalation caused by the electrochemical dissolution of metallic Fe atoms is a major challenge for the practical application of Fe-N-C catalysts. Herein, we construct an efficient single metallic Mn active site to improve the strength of the Fe-N bond, inhibiting the demetalation effect of Fe-N-C. Mn acts as an electron donor inducing more delocalized electrons to reduce the oxidation state of Fe by increasing the electron density, thereby enhancing the Fe-N bond and inhibiting the electrochemical dissolution of Fe. The ORR pathway for the dissociation of Fe-Mn dual sites can overcome the high energy barriers to direct O-O bond dissociation and modulate the electronic states of Fe-N4 sites. The resulting FeMn-N-C exhibits excellent ORR activity with a high half-wave potential (E1/2) of 0.92V in alkaline electrolytes. FeMn-N-C as a cathode catalyst for Zn-air batteries (ZABs) has a cycle stability of 700h at 25°C and a long cycle stability of more than 210h under extremely cold conditions at -40°C. These findings contribute to the development of efficient and stable metal-nitrogen-carbon catalysts for various energy devices. This article is protected by copyright. All rights reserved.

Orbital Hybridization Induced Dipole Polarization and Room Temperature Magnetism of Atomic Co‐N4‐C toward Electromagnetic Energy Attenuation

AbstractManipulating the electronic structure and geometric coordination environment of single metal atoms has been considered as promising approach for enhancing dipole polarization and enriching electromagnetic attenuation mechanisms. However, achieving precise control of the dielectric polarization response at atomic scale remains a huge challenge. Herein, a metal‐acetate coordination complexes‐assisted strategy is proposed to prepare spatially isolated cobalt (Co) atoms embedded in accordion‐like nitrogen‐doped carbon (NC) matrix. The interactions between metal atoms and NC matrix are carefully tailored through the successive evolution of dispersion states of Co species, ranging from individual atoms to atomic clusters to nanoparticles. Density functional theory reveals that the orbital hybridization between the d electrons of embedded Co atoms and p electrons of coordinated N atoms induces the electron redistribution at N sites, enabling enhanced electric dipole polarization and robust room temperature magnetism (a saturation magnetization of 0.108 emu g−1 at 300 K). Consequently, Co‐SAs@NC exhibits optimal electromagnetic wave absorption properties with a minimum reflection loss of ‐54.4 dB and an effective absorption bandwidth of 8.4 GHz. This work demonstrates an efficient strategy for modulating electromagnetic response at atomic level and provides a novel insight into the d/p electrons orbital hybridization between single metal atoms and NC species.

Effect of biaxial tensile-compressive deformation on the optoelectronic properties of monolayers of MoTe2 with adsorbed alkali metals X (X = Li, Na, K, Rb, Cs): a first principles

Based on a first-principles approach, the effects of tensile-compression deformation on the structural stability, electronic structure, and optical properties of monolayers of MoTe2 adsorbed with alkali metal atoms X (X = Li, Na, K, Rb or Cs) were calculated. It was found that the structural stability of the MoTe2 monolayer after adsorption of Li atoms was the most stable, with the smallest adsorption and formation energies and the smallest adsorption height. The movement of the Fermi energy toward the conduction band makes the system an n-type semiconductor. Subsequently, the adsorbed Li-MoTe2 monolayers were selected for tensile-compressive deformation, and with the increase of tensile deformation, the band gap decreased to zero at 10% deformation and exhibited metallic properties. As compressive deformation grows, the band gap shifts from direct to indirect, and metallic characteristics emerge when deformation approaches −10%. The Te-s and Te-p orbital electrons near the Fermi energy level and Mo-d orbitals make the main contribution to the adsorbed alkali metal molybdenum ditelluride system. In terms of optical characteristics, the MoTe2 system after alkali metal adsorption deformation is blue-shifted/ red-shifted at the absorption/reflection peak. These discoveries may help to broaden the possible applications of MoTe2 in low-dimensional electron-emitting devices.