Transition Metal Atoms Research Articles

Thermodynamic Stability Prediction of Triple Transition‐Metal (Ti−Mo−V)3C2${\rm (Ti-Mo-V)}_3{\rm C}_2$ MXenes via Cluster Correlation‐Based Machine Learning

AbstractThe representation of atomic configurations through cluster correlations, along with the cluster expansion approach, has long been used to predict formation energies and determine the thermodynamic stability of alloys. In this work, a comparison is conducted between the traditional cluster expansion method based on density functional theory and other potential machine learning models, including decision tree‐based ensembles and multi‐layer perceptron regression, to explore the alloying behavior of different elements in multi‐component alloys. Specifically, these models are applied to investigate the thermodynamic stability of triple transition‐metal MXenes, a multi‐component alloy in the largest family of 2D materials that are gaining attention for several outstanding properties. The findings reveal the triple transition‐metal ground‐state configurations in this system and demonstrate how the configuration of transition metal atoms (Ti, Mo, and V atoms) influences the formation energy of this alloy. Moreover, the performance of machine learning algorithms in predicting formation energies and identifying ground‐state structures is thoroughly discussed from various aspects.

Advancing electrochemical nitrogen reduction: Efficacy of two-dimensional SiP layered structures with single-atom transition metal catalysts

Researchers are interested in single-atom catalysts with atomically scattered metals relishing the enhanced electrocatalytic activity for nitrogen reduction and 100 % metal atom utilization. In this paper, we investigated 18 transition metals (TM) spanning 3d to 5d series as efficient nitrogen reduction reaction (NRR) catalysts on defective 2D SiPV layered structures through first-principles calculation. A systematic screening identified Mo@SiPV, Nb@SiPV, Ta@SiPV and W@SiPV as superior, demonstrating enhanced ammonia synthesis with significantly lower limiting potentials (−0.25, −0.45, −0.49 and −0.15 V, respectively), compared to the benchmark −0.87 eV for the defective SiP. In addition, the descriptor ΔG*N was introduced to establish the relationship between the different NRR intermediates, and the volcano plot of the limiting potentials were determined for their potential-determining steps (PDS). Remarkably, the limiting voltage of the NRR possesses a good linear relationship with the active center TM atom Ɛd, which is a reliable descriptor for predicting the limiting voltage. Furthermore, we verified the stability (using Ab Initio Molecular Dynamics − AIMD) and high selectivity (UL(NRR)-UL(HER) > -0.5 V) of these four catalysts in vacuum and solvent environments. This study systematically demonstrates the strong catalytic potential of 2D TM@SiPV(TM = Mo, Nb, Ta, W) single-atom catalysts for nitrogen reduction electrocatalysis.

Understanding the role of transition metal implantation on 2D graphitic carbon nitride for solid-state hydrogen storage: A first principles study

Modifying 2D materials with transition metals (TMs) proves to be an effective approach for enhancing their properties in hydrogen storage. In this article, the hydrogen interaction and adsorption over transition metal (TM) atoms (V, Mn, Fe, and Cu) implanted graphitic carbon nitride (gC3N4) is investigated using density functional theory (DFT). The stability of the TM atom on the gC3N4 surface is studied using binding energy and charge density calculations. The adsorption of H2 on the gC3N4 and TM-implanted gC3N4 surfaces is studied using adsorption energy, density of states (DOS), projected density of states (PDOS), charge density difference, and Lowdin occupancy analysis. The obtained results show that the Fe-gC3N4 system exhibits the highest adsorption energy of −1.025 eV for one H2. It is found that each Fe atom implanted on gC3N4 can stably adsorb up to 8H2 molecules, and the average adsorption energy of the 8H2 molecules is −0.201 eV/H2. In the context of practical applications for these materials, desorption is investigated employing the van't Hoff equation. Our findings affirm that the Fe-gC3N4 system can serve as an efficient material for solid-state hydrogen storage.

Regulating the Electron Distribution of Metal-Oxygen for Enhanced Oxygen Stability in Li-rich Layered Cathodes.

Li-rich Mn-based layered oxides (LLO) hold great promise as cathode materials for lithium-ion batteries (LIBs) due to their unique oxygen redox (OR)chemistry, which enables additional capacity. However, the LLOs face challenges related to the instability of their ORprocess due to the weak transition metal (TM)-oxygen bond, leading to oxygen loss and irreversible phase transition that results in severe capacity and voltage decay. Herein, a synergistic electronic regulation strategy of surface and interior structures to enhance oxygen stability is proposed. In the interior of the materials, the local electrons around TM and O atoms may be delocalized by surrounding Mo atoms, facilitating the formation of stronger TM─O bonds at high voltages. Besides, on the surface, the highly reactive O atoms with lone pairs of electrons are passivated by additional TM atoms, which provides a more stable TM─O framework. Hence, this strategy stabilizes the oxygen and hinders TM migration, which enhances the reversibility in structural evolution, leading to increased capacity and voltage retention. This work presents an efficient approach to enhance the performance of LLOs through surface-to-interior electronic structure modulation, while also contributing to a deeper understanding of their redox reaction.

Effect of niobium doping on excitonic dynamics in MoSe2

Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

Study of the optoelectronic properties and the doping effect on different atoms of the CsSnBr3 supercell to absorb visible light: First-principles calculations

Lead-free halide perovskites are prototype materials-based solar cells and many other devices optoelectronic, that have exhibited high power conversion efficiencies, high absorption, and the most important thing is environmentally friendly. This paper presents detailed ab initio calculations of the structural, electronic and optical properties of inorganic perovskite CsSnBr3 by using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). The main objective of this work is to investigate the effects of Mn doped on the optoelectronic properties of CsSnBr3 supercell such as we have substituted the Cs atoms (Cs1−xMnxSnBr3) and Sn atoms (CsSn1−xMnxBr3) respectively by Mn transition metal atoms. The results show that the incorporation of Mn metal in the studied compound improves significantly the optoelectronic properties such that the band gap of CsSnBr3 is 0.546 eV becomes 0.208 eV after doping. The case of the doped samples are the more suitable choice for optoelectronic devices due to the high dielectric constant and a small gap energy, which shows a low recombination rate, and consequently, improves the device performance especially in the visible energy range (1.65–3.26 eV).

First-principles study of sulfur-host materials utilizing single-atom catalysts embedded within g-C3N4

The performance of lithium-sulfur batteries (LSBs) is limited by the shuttle effect and the conversion between lithium polysulfides (LiPSs). In this study, based on first-principles calculations, we thoroughly investigated the anchoring and catalytic effects of transition metal atom-embedded g-C3N4 (TM@g-C3N4, TM = Fe, Co, Ni) as sulfur host materials for LSBs. COHP calculation results demonstrate that TM@g-C3N4 effectively anchors LiPSs by forming Li-N and TM-S bonds, suppressing the shuttle effect, and enhancing the electrochemical performance. The density of states (DOS) results indicate that the introduction of transition metal atoms improves the conductivity, rendering the entire adsorption system metallic, which helps maintain good conductivity of sulfur-loaded cathode materials during charge and discharge processes. Among them, Ni@g-C3N4 exhibits superior performance by effectively anchoring LiPSs (1.98–4.21 eV) and significantly reducing the free energy of sulfur reduction reaction (0.07 eV). This study provides new insights into the development of sulfur host materials with strong anchoring capability and excellent catalytic activity, and serves as a reference for g-C3N4 loaded with transition metal atoms as high-quality cathode materials.

Theoretical designs of ORR/OER single‐atom catalysts TM@Ti2CT2 (T = O, S, Cl)

AbstractDriven by the goal of establishing a fossil‐fuel‐free and nuclear‐power‐free economy based on renewable energy, metal‐air batteries are regarded as promising energy conversion and storage devices. Developing efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts for the air electrode of metal‐air batteries is becoming increasingly important. In this work, 36 transition metal (TM) single‐atom catalysts are designed based on MXenes Ti2CT2 with different surface terminal atoms (T = O, S, Cl), and their ORR/OER catalytic activity and stability are evaluated by the density functional theory. Ni@Ti2CO2, Pd@Ti2CS2, and Co@Ti2CCl2 are found to exhibit good catalytic activity with ORR/OER overpotentials of .54 V/.62 V, .59 V/.29 V, .44 V/.40 V. The aggregation behavior of three catalysts is estimated by comparing the average binding energy of one, two, three, and four TM atoms anchored on Ti2CT2. This work cannot only provide a theoretical guide to develop bifunctional single‐atom catalysts, but also help us understand the effect of terminal atoms on the electronic structures and catalytic activity of TM@Ti2CT2.

C(sp3)-C(sp3) Coupling of Cycloalkanes and Alkyl Halides via Dual Photocatalytic Hydrogen Atom Transfer and Nickel Catalysis.

Functionalization of C(sp3)-H bonds represents the most straightforward and atom-economical transformation in organic synthesis. An innovative approach integrating photocatalytic hydrogen atom transfer (HAT) and transition metal catalysis has made significant progress in the coupling of α-heterosubstituted C-H bonds with alkyl halides. However, unactivated alkanes were ineffective as a result of the preponderance of byproduct formation. Herein, we demonstrate direct HAT and nickel catalysis in the coupling of cycloalkanes and benzyl bromides/primary alkyl iodides. Additionally, tetrabutylammonium decatungstate (TBADT) was recovered and recycled.

Photocatalytic Efficiency for CO2 Reduction of Co and Cluster Co2O2 Supported on g-C3N4: A Density Functional Theory and Machine Learning Study.

It is well known from experimental results that a single atom of cobalt supported on g-C3N4 is an efficient photocatalyst for the reduction of CO2 to CO, with a better photocatalytic activity than g-C3N4. In this work, we investigate the performance as catalysts for the CO2 reduction of single atoms of cobalt and Co2O2 clusters supported on graphitic carbon nitride (g-C3N4). Employing density functional theory plus Hubbard (DFT + U) calculations, we investigate in detail the reduction mechanisms to CO and HCOOH for the first time. We find that deposition of cobalt on g-C3N4 decreases the work function of g-C3N4 to 6.6 eV and provides a better candidate for the reduction reaction. In addition, we find that the preferred product of CO2 reduction on Co@g-C3N4 is CO, with a rate-determining barrier of 0.97 eV, while on Co2O2@g-C3N4, CO2 reduces to formate with a rate-determining barrier of 0.44 eV. We determine the creation of CO2 from COOH to only take place on Co2O2@g-C3N4, with a (relatively high) barrier of 2.27 eV. In order to obtain more easily the transition state energies of the reactions mentioned above, we applied machine learning methods to search for high-importance descriptors for these quantities, in the case of single transition metal atoms supported on C3N4. Interestingly, our results show that our quantities of interest are closely related to the adsorption energies of products and normalized valence electrons of the products of the elementary reactions as well as those of the metal atoms. The former of these two sets of features can be straightforwardly obtained via DFT, while the latter energies are extensively tabulated. Our results offer guidance for the design of catalysts and photocatalysts for CO2 reduction on single-metal atoms supported on C3N4.

Loading of Single Atoms of Iron, Cobalt, or Nickel to Enhance the Electrocatalytic Hydrogen Evolution Reaction of Two-Dimensional Titanium Carbide.

The rational design of advanced electrocatalysts at the molecular or atomic level is important for improving the performance of hydrogen evolution reactions (HERs) and replacing precious metal catalysts. In this study, we describe the fabrication of electrocatalysts based on Fe, Co, or Ni single atoms supported on titanium carbide (TiC) using the molten salt method, i.e., TiC-FeSA, TiC-CoSA, or TiC-NiSA, to enhance HER performance. The introduction of uniformly distributed transition-metal single atoms successfully reduces the overpotential of HERs. Overpotentials of TiC-FeSA at 10 mA cm-2 are 123.4 mV with 61.1 mV dec-1 Tafel slope under acidic conditions and 184.2 mV with 85.1 mV dec-1 Tafel slope under alkaline conditions, which are superior to TiC-NiSA and TiC-CoSA. TiC samples loaded with transition-metal single atoms exhibit high catalytic activity and long stability under acidic and basic conditions. Density functional theory calculations indicate that the introduction of transition-metal single atoms effectively reduces the HER barrier of TiC-based electrocatalysts.

Unlocking Ultrafast Spin Transfer in Single-Magnetic-Center-Decorated Triangulene Systems.

Triangulene, as a typical open-shell graphene fragment, has attracted widespread attention for nanospintronics, promising to serve as building blocks in spin-logic units. Here, using ab initio calculations, we systematically study the laser-induced ultrafast spin-dynamic processes on triangulene nanoflakes, decorated with a transition-metal atom. The results reveal a competition between the induced magnetic center and the carbon edge of the triangulene, resulting in the coexistence of dual spin-density-distribution patterns on such single-magnetic-center systems, thus opening up possibilities of complex spin-dynamic scenarios beyond the spin flip. Interestingly, no matter what direction the spin points to, it is possible to achieve reversible spin-transfer processes using the same laser pulse. Increasing the pool of elementary processes to contain not only spin-direction-dependent but also spin-direction-independent scenarios allows for more versatile spin-logic operations, including classical handling of information and quantum computing. In the present work, we suggest downscaling nanospintronic devices by integrating triangulene-based nanostructures.

Heterokaryotic transition-metal dimers embedded monolayer g-C3N3 as promising anchoring and electrocatalytic materials for lithium-sulfur battery: First-principles calculations

g-C3N3 not only has high content of pyridine nitrogen, but also has a special two-dimensional porous structure, which is an ideal diatomic catalytic host materials. In this work, homonuclear and heteronuclear dual-atom catalysts (DACs, TM-TM@g-C3N3, TM = Mn, Fe, Co, Ni) were constructed using single-layer g-C3N3 as the carrier material of DACs, and their potential as sulfur-hosting materials and electrocatalytic materials for lithium-sulfur batteries was explored through first principles comprehensively. The results show that the coupling between the two metal atoms in heteronuclear DACs can regulate the spin state of each other's d-electrons, so that the anchoring and catalytic effects of heteronuclear DACs on polysulfide are more excellent than that of homonuclear DACs. Co-Mn@g-C3N3, when utilized as the cathode material in lithium-sulfur batteries, offers exceptional properties due to the hybridization between Mn2+ high-spin state d electron and Co2+ half-filled dz2 orbital. This unique interaction not only enables the polysulfide to exhibit the lowest Gibbs free energy during conversion, but also results in the lowest reaction energy barrier of 0.26 eV for the conversion of Li2S2 to Li2S. Furthermore, it is found that when 3d transition metal atoms act as heteronuclear DACs, the coupling between metal ions with high-spin states at the active site and metal ions with empty orbitals or half-full d-electrons has the most significant catalytic effect on polysulfides.

Understanding the effect of foreign atoms occupation on the metamagnetic behaviors in MnCoSi-based alloys: taking Pt-doping as an example

Present research on TiNiSi-type MnCoSi-based alloys focuses on finding a suitable doping element to effectively reduce the critical magnetic field (μ 0 H cri) required to induce a metamagnetic transition. This paper provides a guide to achieve this goal through an experimental investigation of Mn1−x Pt x CoSi and MnCo1−x Pt x Si alloys. In Mn1−x Pt x CoSi, as x increases, μ 0 H cri at room temperature decreases, while in MnCo1−x Pt x Si, it increases. This phenomenon can be attributed to the fact that larger Pt atoms prefer Co sites over Mn sites, as predicted by our density-functional theory. Consequently, in Mn1−x Pt x CoSi, larger Co atoms are extruded into the Mn atoms chain, increasing the nearest Mn–Mn distance and resulting in a reduced μ 0 H cri. This finding suggests that transition-metal atoms with more valence electrons preferably occupy the Co site, while those with fewer valence electrons preferably occupy the Mn site. Adhering to this rule, one can easily obtain a low μ 0 H cri and large magnetostrain under a low magnetic field by selecting a suitable foreign element and chemical formula, as demonstrated by the Mn1−x Pt x CoSi alloy.

Sensing behavior of modified two-dimensional GeTe monolayer to detect air discharge components: A first-principles study

It is crucial to determine the operating condition of air-insulated equipment by monitoring air discharge components (O3, NO2, CO) to detect any occurrence of partial discharges (PD). Although GeTe is widely applied in gas sensing technology, its performance in selective detection is relatively subpar. This study investigatesthe modification of structures of GeTe monolayers by doping single transition-metal (TM) atom (Fe, Co, Ir, Pt, Pd, and Rh) to enhance its gas adsorption capability and selectivity of different doped GeTe monolayers to gases according to competitive adsorption. Multiple properties such as adsorption energy, charge transfer, charge difference density (CDD), density of states (DOS), occupation function, desorption time, and work function were discussed, indicating that doped GeTe exhibits greater adsorption capabilities. Specifically, Ir-GeTe demonstrates the highest absolute value of adsorption energy for O3 at 2.75 eV, while Co-GeTe exhibits the highest absolute value of adsorption energy for NO2 at 2.13 eV. Furthermore, the analysis of atomic orbital overlap reveals stronger chemical interactions between Ir-GeTe and O3, as well as Co-GeTe and NO2. Considering selectivity and working function, Fe-GeTe emerges as a potential sensing material for detecting NO2. This research offers promising and practical applications for single TM atom-doped GeTe as gas-sensitive materials.

Engineering Spin Polarization of the Surface-Adsorbed Fe Atom by Intercalating a Transition Metal Atom into the MoS2 Bilayer for Enhanced Nitrogen Reduction.

The precise control of spin states in transition metal (TM)-based single-atom catalysts (SACs) is crucial for advancing the functionality of electrocatalysts, yet it presents significant scientific challenges. Using density functional theory (DFT) calculations, we propose a novel mechanism to precisely modulate the spin state of the surface-adsorbed Fe atom on the MoS2 bilayer. This is achieved by strategically intercalating a TM atom into the interlayer space of the MoS2 bilayer. Our results show that these strategically intercalated TM atoms can induce a substantial interfacial charge polarization, thereby effectively controlling the charge transfer and spin polarization on the surface Fe site. In particular, by varying the identity of the intercalated TM atoms and their vacancy filling site, a continuous modulation of the spin states of the surface Fe site from low to medium to high can be achieved, which can be accurately described using descriptors composed of readily accessible intrinsic properties of materials. Using the electrochemical dinitrogen reduction reaction (eNRR) as a prototypical reaction, we discovered a universal volcano-like relation between the tuned spin and the catalytic activity of Fe-based SACs. This finding contrasts with the linear scaling relationships commonly seen in traditional studies and offers a robust new approach to modulating the activity of SACs through interfacial engineering.

First principles study of hydrogen storage on B-doped SiC monolayers through light transition metal atoms

In this first-principles study, based on Density Functional Theory, we assess the capacity of metal-decorated, boron-doped, graphene-like monolayers of silicon carbide (SiC) to adsorb hydrogen molecules. To enhance the binding of metal adatoms on SiC monolayers, these were substitutionally doped with boron atoms. Alkaline, alkaline-earth, and transition metal adatoms were considered and their hydrogen storage capabilities were compared. The results show that alkaline-earth metal adatoms are not suitable for hydrogen storage. On the other hand, sodium- and potassium-decorated B-doped SiC monolayers adsorb the largest number of H2 molecules per adatom, but their adsorption energies are insufficient for an adequate hydrogen storage. Titanium and scandium adatoms are the most suitable for hydrogen storage since they exhibit good adsorption energies and up to four and five H2 molecules per adatom, respectively. Moreover, the estimated potential barriers for diffusion of these two adatoms on the B-doped SiC monolayers indicate that the probability of clustering is very low. Moreover, within the ideal-gas approximation, it is estimated that hydrogen can be stored in the Ti- and Sc-decorated monolayers at room temperature and atmospheric pressure. Furthermore, if SiC monolayers were doped with boron atoms in concentrations similar to those reported for graphene, it is estimated that the gravimetric capacities could reach 5.1 wt% and 6.3 wt% for Ti-decorated and Sc-decorated monolayers, respectively, which are close to the target hydrogen-storage capacities envisioned for the near future.

Unveiling diverse coordination-defined electronic structures of reconstructed anatase TiO2(001)-(1 × 4) surface

Transition metal oxides (TMOs) exhibit fascinating physicochemical properties, which originate from the diverse coordination structures between the transition metal and oxygen atoms. Accurate determination of such structure-property relationships of TMOs requires to correlate structural and electronic properties by capturing the global parameters with high resolution in energy, real, and momentum spaces, but it is still challenging. Herein, we report the determination of characteristic electronic structures from diverse coordination environments on the prototypical anatase-TiO2(001) with (1 × 4) reconstruction, using high-resolution angle-resolved photoemission spectroscopy and scanning tunneling microscopy/atomic force microscopy, in combination with density functional theory calculation. We unveil that the shifted positions of O 2s and 2p levels and the gap-state Ti 3p levels can sensitively characterize the O and Ti coordination environments in the (1 × 4) reconstructed surface, which show distinguishable features from those in bulk. Our findings provide a paradigm to interrogate the intricate reconstruction-relevant properties in many other TMO surfaces.

Computational screening of transition metal anchored C9N10 as the highly active and selective electrocatalysts for NH3 synthesis

Electrochemical nitrogen reduction reaction (NRR) is a very prospective approach for generating green and sustainable NH3 under mild conditions. However, the development of NRR electrocatalysts with high performance remains a huge hurdle in the field of energy conversion today. Herein, by means of first-principles calculations, we employed a hierarchical screening strategy of structural stability, catalytic activity, and selectivity to systematically investigate the potentials of a series of transition metal atoms anchored on g-C9N10 (TM@C9N10) as the electrocatalysts for NRR. Particularly, we proposed the multiple-level descriptors (φ and ICOHP), realizing the preliminary prescreening of numerous candidates. The results reveal that V@C9N10 and W@C9N10 stand out from all candidates with the significantly low limiting potentials of −0.17 V and −0.26 V, respectively. Meanwhile, they can efficiently suppress the competing hydrogen evolution reaction. Such the outstanding activity can be attributed to the donation-feedback process between the d-electrons of V and W atoms and the anti-orbitals of *N2, as well as the efficient charge transfer in hydrogenation steps. Our work not only broadens the theoretical foundation for the rational design of highly efficient SACs, but also provides an attempt to develop the NRR electrocatalysts with high activity and selectivity.

First-principles study on rare earth-based equiatomic quaternary Heusler alloys YbCoCrSb and YbCoTiSn: New candidates for spintronics

We have investigated the structural, mechanical, thermal, electronic, magnetic, and half-metallic properties of new Yb-based EQHAs such as YbCoCrSb and YbCoTiSn using first-principles calculations. We computed the ground state properties of different possible crystal structures and magnetic states. We also calculated their elastic constants and derived mechanical parameters, including bulk, shear, and Young's moduli, as well as Poisson's and Pugh ratios. The electronic structure of both EQHAs shows half-metallic behavior with a spin down band gap of 0.39 eV for YbCoCrSb and 0.30 eV for YbCoTiSn in the GGA-PBE scheme. The estimated total spin magnetic moment has a positive integer value, which is well in accordance with the Slater-Pauling rule of 18. Because of the nearly closed f orbital shell of the Yb atom, the total spin magnetic moment is mainly dependent on 3d transition metal atoms. These alloys exhibit TC > 300 K using the mean field approximation.