Doping Of Transition Metal Atoms Research Articles

Single atom catalysts with anion center toward oxygen electrocatalysis based on the conductive 1T-HfTe2

Advancing efficient catalysts for oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) is imperative for commercializing emerging energy devices. Using density functional theory (DFT) calculations, we propose doping different transition metal (TM) atoms to regulate the electronic structures of the two-dimensional 1T-HfTe2 monolayer to achieve bifunctional catalysis for the ORR/OER. Due to the small electronegativity of the Hf atom, we found the doped TMs can generally form anion centers by accepting abundant charges from the Hf interlayer. At the same time, the highly conductive 1T-HfTe2 contributes to the charge transfer between the active center and the reaction intermediates, rendering the designed SACs the tunable activity for the reactions. By comparing the theoretical overpotentials of ORR and OER on 15 single-atom catalysts (SACs), Pt-doped system exhibits excellent catalytic activity for both ORR and OER, outperforming the traditional Pt(111) and RuO2(110) catalysts. Based on the charge transfer mechanism, we clarified that the doped TM atoms act as a ‘bridge’ to transfer the electrons from the substrate to the reaction intermediates, thereby effectively contributing to the improvement of catalytic activity. In summary, our study shows that, by doping appropriate TM atoms, the intrinsic inert HfTe2 can be activated toward efficient ORR/OER. This could provide some guidance for the design of new two-dimensional ORR/OER bifunctional catalyst materials.

Enhancing CO2 electroreduction performance through transition metal atom doping and strain engineering in γ-GeSe: a first-principles study.

The development of electrocatalysts that exhibit stability, high activity, and selectivity for CO2 reduction reactions (CO2RR) remains a significant challenge. Single-atom catalysts (SACs) hold promise in addressing this challenge due to their high atomic utilization efficiency. In this study, we explore the potential of monolayer γ-GeSe doped with transition metals, referred to as TM@γ-GeSe, for facilitating electrocatalytic CO2RR. Among the 26 TM@γ-GeSe SACs systematically designed, we have identified four stable transition metal catalysts (TM = Rh, Pd, Pt, and Au). Mechanistic investigations into the CO2RR pathways reveal exceptional electrocatalytic activity for Rh@γ-GeSe and Pd@γ-GeSe, with limiting potentials of -0.26 and -0.35 V, respectively. Particularly, Pd@γ-GeSe exhibits outstanding product selectivity toward formic acid. The introduction of strain engineering induces modifications in the catalytic activity and selectivity of Rh@γ-GeSe. Notably, a 1% tensile strain promotes formic acid as the preferred product, thereby improving the specific product selectivity of Rh@γ-GeSe. Conversely, compressive strain reduces CO2RR activity while enhancing the hydrogen evolution reaction, leading to a decrease in CO2RR selectivity. Furthermore, we use the work function as a descriptor to elucidate the underlying mechanism of strain tunability. We hope that our theoretical study will offer valuable insights for the design of catalysts based on γ-GeSe for electrocatalytic CO2RR.

Controllable high Curie temperature through 5d transition metal atom doping in CrI3

Two-dimensional (2D) CrI3 is a ferromagnetic semiconductor with potential for applications in spintronics. However, its low Curie temperature (T c) hinders realistic applications of CrI3. Based on first-principles calculations, 5d transition metal (TM) atom doping of CrI3 (TM@CrI3) is a universally effective way to increase T c, which stems from the increased magnetic moment induced by doping with TM atoms. T c of W@CrI3 reaches 254 K, nearly six times higher than that of the host CrI3. When the doping concentration of W atoms is increased to above 5.9%, W@CrI3 shows room-temperature ferromagnetism. Intriguingly, the large magnetic anisotropy energy of W@CrI3 can stabilize the long-range ferromagnetic order. Moreover, TM@CrI3 has a strong ferromagnetic stability. All TM@CrI3 change from a semiconductor to a half-metal, except doping with Au atom. These results provide information relevant to potential applications of CrI3 monolayers in spintronics.

Modulation of magnetism in transition-metal-doped monolayer MoS2 by strain engineering

It is important to induce and manipulate magnetism in two-dimensional materials for developing low-dimensional spintronic devices. Here we explored the modulation of magnetism in MoS2 monolayers doped with 3d and 4d transition-metal (TM) atoms by strain engineering using first-principles calculations. It is found that 3d TM atom doping tends to induce high spin in TM-MoS2 monolayers, while 4d TM atom doping tends to induce low spin. The magnetic states in TM-MoS2 monolayers can be further mediated by TM-S bond interaction and change of crystal structure symmetry, which is achieved by strain engineering. An increase in the ionic bonding interaction of TM-S modulated by strain leads to an increase of the unpaired electrons accumulated on the TM and S atoms, thus giving rise to the interesting variation in the magnetic moments with strain. Strain is also able to modulate the crystal structures to undergo or not Jahn-Teller (J-T) distortion effects. The structures having J-T distortion will result in low spin states. The research results offer important theoretical support for further application of strain-driven spin devices on MoS2 nanostructures.

Defect engineered Janus MoSiGeN4 as highly efficient electrocatalyst for hydrogen evolution reaction

It is well known that defect engineering is very important to the improvement of catalyst activity. In this paper, defect engineering is introduced into Janus MoSiGeN4 to regulate hydrogen evolution reaction (HER) activity. Based on density functional theory, a theoretical study is carried out to clarify the roles of vacancy and transition metal (TM) atom doping in Janus MoSiGeN4. Five different vacancies are considered, and results suggest that outmost N vacancy can effectively enhance the HER activities. For VN2@MoSiGeN4 and VN1@MoSiGeN4 structures, the hydrogen adsorption Gibbs free energy (ΔGH*) is 0.015 eV and 0.145 eV, respectively. Moreover, a systematic screening of eleven non-precious TM atoms (V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ta and W) doped MoSiGeN4 as HER catalysts reveals that Fe-, Mn-, and Nb-doped MoSiGeN4 show better HER activity than that of Pt with theΔGH* of 0.013 eV, 0.061 eV, and 0.087 eV, respectively. Electronic properties, electron charge density difference and Bader charge are employed to explore the origin of electrocatalytic activity. Our study confirms that vacancy and TM atom doping are effective means to enhance electrocatalytic performance and defect engineered Janus MoSiGeN4 can be served as highly efficient HER catalyst.

Electrocatalytic nitrogen fixation performance of two-dimensional Metal-Organic Frameworks Cu3(C6O6) and TM/Cu3(C6O6) from first-principle study

Electrochemical nitrogen reduction reaction can convert N2 into NH3 under ambient conditions, which is a friendly method of ammonia synthesis. Many studies have shown that two-dimensional Metal-Organic Framework (2D-MOF) materials have potential applications in the field of catalysis. In this paper, we systematically studied different single-atom catalysts (SACs) TM/Cu3(C6O6) by the density functional theory (DFT), and screened out two suitable candidate catalysts. Fe/Cu3(C6O6) and Co/Cu3(C6O6) catalysts have the excellent catalytic activity with the limiting potentials of −0.92 V and −0.97 V respectively. And it reveals that doping transition metal atoms can effectively improve the catalytic activity of Cu3(C6O6). Interestingly, we analyzed the electronic band structures and the density of state (DOS) of the catalysts, the results show that they have metallic properties and have good electrical conductivity. Therefore, Fe/Cu3(C6O6) and Co/Cu3(C6O6) are promising catalysts for NRR. Our study provides a new idea for the design of high-efficiency nitrogen reduction catalysts.

Theoretical calculation of hydrogen evolution reaction in two-dimensional As2X3(X=S, Se, Te) doped with transition metal atoms

In this paper, density functional theory (DFT) was used to investigate the hydrogen evolution reaction (HER) performance of vacant As2X3(X = S, Se, Te), which is doped with transition metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). The results show that the X-vacancy of As2X3 is stable and can tune the HER activity. According to the scaling relation of Gibbs free energy variation of H* intermediate, the volcano diagram and exchange current density diagram are established. The Co@As2S3 (ΔGH∗ = -0.09 eV), Co@As2Se3 (ΔGH∗ = -0.06 eV) and Cu@As2Te3 (ΔGH∗ = 0.04 eV) systems show good HER performance. Therefore, our research highlights an efficient electrocatalyst for HER with single transition metal atom doping based on As2X3 systems.

Computational screening toward transition metal doped vanadium carbides in different crystal planes for efficient hydrogen evolution: a first-principles study.

In the present work, we evaluated the hydrogen evolution reaction (HER) performance of transition metal (Co, Fe, Ni, Mn, and Mo) doped vanadium carbides (VC). In addition, the doping atoms were screened separately on the (100), (110) and (111) crystal planes to analyze the differences in HER activities. Among all the calculated models, Mn-VC(100) exhibited the best catalytic hydrogen evolution performance with a Gibbs free energy for hydrogen adsorption (ΔGH*) of 0.0012 eV. Doping Mn greatly improved the HER performance of VC(100) by enhancing the adsorption of hydrogen on the catalyst surface. The analysis of the electronic density of states and charge transfer confirmed that doping transition metal atoms into the surfaces of the VC model successfully optimized the electronic structure and promoted catalytic reaction kinetics. Besides, the relationship between the catalytic activity and pH value of different models was considered, and doping Co atoms on the (100) crystal plane could effectively modify the pH value range applicable for the efficient HER. Interestingly, even if the same metal atoms were doped, various active sites of VC models exhibited different catalytic performances due to disparate exposed crystal planes and pH values. This indicates that the main exposed crystal surfaces and the pH range of application need to be considered when selecting the appropriate doping element for the catalyst.

Embedding Group VIII Elements into a 2D Rigid pc-C3N2 Monolayer to Achieve Single-Atom Catalysts with Excellent OER Activity: A DFT Theoretical Study

Under DFT calculations, a systematic investigation is carried out to explore the structures and oxygen evolution reaction (OER) catalytic activities of a series of 2D single-atom catalyst (SAC) systems, which are constructed by doping the transition metal (TM) atoms in group VIII into the cavities of rigid phthalocyanine carbide (pc-C3N2). We can find that when Co, Rh, Ir and Ru atoms are doped in the small or large cavities of a pc-C3N2 monolayer, they can be used as high-activity centers of OER. All these four new TM@C3N2 nanostructures can exhibit very low overpotential values in the range of 0.33~0.48 V, even smaller than the state-of-the-art IrO2 (0.56 V), which indicates considerably high OER catalytic activity. In particular, the Rh@C3N2 system can show the best OER performance, given that doped Rh atoms can uniformly serve as high-OER-active centers, regardless of the size of cavity. In addition, a detailed mechanism analysis was carried out. It is found that in these doped pc-C3N2 systems, the number of outer electrons, the periodic number of doped TM atoms and the size of the embedded cavity can be considered the key factors affecting the OER catalytic activity, and excellent OER catalytic performance can be achieved through their effective cooperation. These fascinating findings can be advantageous for realizing low-cost and high-performance SAC catalysts for OER in the near future.

Single atom catalysts supported on metallic C5N monolayers for oxygen reduction/evolution reactions with more active sites than loaded metal atoms

Single atom catalysts (SACs) supported by carbonaceous materials present extraordinary activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which however suffer from low loadings of transition metal (TM) atom. We here proposed a strategy of designing SACs toward ORR/OER containing higher number of active sites than that of loaded TM atoms, which include not only the metal centers but also the non-metal atoms activated by the doping of TM atoms. By incorporating TM atoms of Fe, Co and Ni into our previously predicted metallic monolayers of C5N, we investigated their ORR/OER activities and found that orthorhombic-C5N supported Co atoms coordinated with three C atoms and one N atom can serve as superior bifunctional electrocatalysts for both ORR and OER with overpotentials of 0.38 and 0.3 V, respectively. Our density functional theory calculations also demonstrate that the structural configurations of the first, second and even outer coordination sphere of metal centers can simultaneously affect the catalytic performance of SACs. This study provides a novel idea to address the challenge faced by the SACs toward ORR/OER caused by the low loadings of TM atoms and obscure structure-property relationship.

Effect of vacancy defect and dopants on the sensitivity of germanene to H2CO

The geometric and electronic structures, magnetism, and recovery time of vacancy-defected and doped germanene, which is used as a sensor for the detection of H 2 CO molecule, are examined using first-principles calculation methods. The results reveal that the introduction of vacancy and transition metal dopants (V, Cr, Mn, Fe) increases the adsorption stability of H 2 CO on germanene. In addition, V-doped vacancy-defected germanene (V-VGe) is converted from semiconductor to conductor by absorbing H 2 CO molecules, which can be used as an obvious signal to detect H 2 CO gas. Furthermore, the strong interaction with H 2 CO and the short recovery time indicates that V-VGe is most sensitive to the H 2 CO molecules. Overall, the findings of this study provide theoretical reference for the design of a new H 2 CO gas sensor. First-principles calculation method based on density functional theory is used to study the effect of vacancy and transition metal dopants (V, Cr, Mn, Fe) on the adsorption of H 2 CO on germanene.The results show that doping effectively improves the sensitivity of the vacancy-defected germanene to H 2 CO molecule. • The appearance of vacancy defects enhances the sensitivity of the germanene substrate. • Doped transition metal atoms (V, Cr, Mn, Fe) can improve the adsorption capacity of vacancy-defective germanene to H 2 CO molecules. • Vacancy-defective germanene doped with V atoms can be used to detect H 2 CO molecules.

Theoretical study on the mechanism of CO2 adsorption and reduction by single-atom M (M = Cu, Co, Ni) doping C2N

The capture and further conversion of carbon dioxide into useful fuels and value-added chemicals is critical to addressing the growing problem of global warming and promoting sustainable human development. In this work, the adsorption and activation of CO2 on the surface of single-atom-doped C2N monolayers and the first-step reaction mechanism of CO2RR were investigated by density functional theory (DFT). The catalyst structure, CO2 adsorption configuration and electronic properties of CO2 activation on C2N surfaces decorated with transition metal single atoms of Cu, Co, and Ni were discussed. Cu/C2N, Co/C2N and Ni/C2N all have good CO2 adsorption performance by calculations. The calculation results of the first hydrogenation reaction of CO2RR show that the three materials of Cu/C2N, Co/C2N and Ni/C2N have lower energy barriers than the pristine C2N, which suggests that they are more favorable for the CO2RR reaction to proceed. The Cu/C2N surface is more inclined to adsorb CO2 and then combine with H atoms to form OCHO, but the Co/C2N and Ni/C2N surfaces are more inclined to hydrogenate CO2 to COOH in one step. The difference in the mechanism of the three material systems may be due to the difference of electrons and density of states on the 4s orbital of the outermost electron number of the doped transition metal atoms Cu, Co, Ni.

Enhancing hydrogen evolution reaction performance of transition metal doped two-dimensional electride Ca2N

Two-dimensional electride Ca2N has strong electron transfer ability and low work function, which is a potential candidate for hydrogen evolution reaction (HER) catalyst. In this work, based on density functional theory calculations, we adopt two strategies to improve the HER catalytic activity of Ca2N monolayer: introducing Ca or N vacancy and doping transition metal atoms (TM, refers to Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ru, Hf, Ta and W). Interestingly, the Gibbs free energy ΔGH∗ of Ca2N monolayer after introducing N vacancy is reduced to -0.146 eV, showing good HER catalytic activity. It is highlighted that, the HER catalytic activity of Ca2N monolayer can be further enhanced with TM doping, the Gibbs free energy ΔGH∗ of single Mo and double Mn doped Ca2N are predicted to be 0.119 and 0.139 eV, respectively. The present results will provide good theoretical guidance for the HER catalysis applications of two-dimensional electride Ca2N monolayer.

Modulating of electronic states and magnetic polarization in monolayered 1T-HfSe2 under non-metal atom and transition metal atom doping

Doping is very effective in regulating the properties of two-dimensional materials. Based on the first principles of density functional theory, the effects of the electronic and magnetic properties on the 1T-HfSe2 monolayer with single doping of non-metallic atoms (NM) and transition metal atoms (TM) and co-doping of metal and non-metallic atoms are systematically studied. We find that N, P and As exhibit non-magnetic metal properties. In contrast, F, Br and I exhibit magnetic semiconductor properties. The F-doped system retains the magnetic semiconductor properties under (−6%–10%) strain, and the band gap varies from 0.131 eV to 1.122 eV. Magnetic moments are generated outside the Ni atom doping system for metal atom doping. For metal and non-metal atoms doping, due to the interaction between TM and NM, found that not only can it produce massive magnetic moment and stimulate the initially did not produce a magnetic moment of non-metal atoms magnetic moment. The influence of increasing doping concentration on performance was further considered. It was found that the nearest neighbor position of the metal atom and non-metal atom was the most structurally stable, and the magnetic moment also changed when the distance between the metal atom and non-metal atom changed. These results have a specific significance for developing spintronic devices based on HfSe2.

Transition metal anchored on C9N4 as a single-atom catalyst for CO2 hydrogenation: A first-principles study

To alleviate the greenhouse effect and maintain the sustainable development, it is of great significance to find an efficient and low-cost catalyst to reduce carbon dioxide (CO2) and generate formic acid (FA). In this work, based on the first-principles calculation, the catalytic performance of a single transition metal (TM) (TM = Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, Au, or Hg) atom anchored on C9N4 monolayer (TM@C9N4) for the hydrogenation of CO2 to FA is calculated. The results show that single TM atom doping in C9N4 can form a stable TM@C9N4 structure, and Cu@C9N4 and Co@C9N4 show better catalytic performance in the process of CO2 hydrogenation to FA (the corresponding maximum energy barriers are 0.41 eV and 0.43 eV, respectively). The partial density of states (PDOS), projected crystal orbital Hamilton population (pCOHP), difference charge density analysis and Bader charge analysis demonstrate that the TM atom plays an important role in the reaction. The strong interaction between the 3d orbitals of the TM atom and the non-bonding orbitals (1π g) of CO2 allows the reaction to proceed under mild conditions. In general, our results show that Cu@C9N4 and Co@C9N4 are a promising single-atom catalyst and can be used as the non-precious metals electrocatalyst for CO2 hydrogenation to formic acid.

Ferromagnetism in V and Cr doped ScN diluted magnetic semiconductor in B3 phase: A DFT study

As researchers at present are showing a great interest in nitrides as materials for spintronics applications, we have analyzed the effects of doping with magnetic transition-metal elements (TM = V, Cr) on the electronic and magnetic properties of semiconducting scandium nitride. We have determined the structural, electronic and magnetic properties of pure ScN and transition metal doped Sc1-xZxN (Z = V, Cr) in zinc blende (ZB) phase at x = 0.25 in this paper. The Siesta Initiative electronic properties of thousand atoms (SIESTA) code within the density functional theory (DFT) and generalized gradient approximation (GGA)+U, due to Perdew-Burke-Ernzerhof (PBE) has been used to estimate the exchange-correlation functional. Our band structure results for ScN shows the semiconductor nature with indirect band gap whereas Sc1-xVxN and Sc1-xCrxN show the half metallic behavior. The lattice parameters and volume are modified by doping of transition metal atoms. The obtained results are in excellent agreement with earlier reported data.

Doping-driven electronic structure and conductivity modification of nickel sulfide.

The lack of electrical conductivity limits the electrochemical kinetic rate of the electrode material, resulting in the inability to reach its theoretical capacity. A facile method is adopted to improve the intrinsic conductivity of binary NiS2/Ni3S4 hybrid nickel sulfide, with the doping of transition metal atoms Co, Mn and Ag. Through the introduction of heteroatoms, the electronic structure of the electrode material is modified and the electrical conductivity is significantly improved, thus enhancing its electrochemical performance. The improvement of conductivity is attributed to the formation of intermediate bands of transition metals and the redistribution of electrons, and the result is demonstrated by experimental and density functional theory (DFT) calculations. As a result, the NiS2/Ni3S4hybrid nickel sulfide after 0.5% amount of Co-doping reaches the highest specific capacitance of 2874 F g-1 at 1 A g-1, increasing specific capacitance of 653 F g-1 as 29.4% of the specific capacitance of non-doped nickel sulfide. The Co doped nickel sulfide also exhibits remarkable cycling stability compared with non-doped nickel sulfide. The assembled 2% Co-doped nickel sulfide//rGO, 0.5% Mn-doped nickel sulfide//rGO and 0.5% Ag-doped nickel sulfide//rGO asymmetric supercapacitors show a specific energy density of 36.6, 36.1 and 36.0 W h kg-1 at a power density of 800 W kg-1. This study provides a useful insight into the fabrication of high performance pseudocapacitive materials.

Computational screening of transition-metal doped boron nanotubes as efficient electrocatalysts for water splitting.

The search for efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of utmost importance for the production of hydrogen and oxygen via water splitting. In this work, the catalytic performance of the OER and HER on transition metal doped boron nanotubes (BNTs) was investigated using density functional theory. It was found that the doped transition metal atoms determine the catalytic activity of the BNTs. Rhodium-doped BNTs exhibited excellent OER activity, while cobalt-doped BNTs displayed great catalytic activity toward the HER. Volcano relationships were found between the catalytic activity and the adsorption strength of reaction intermediates. Rhodium- and cobalt-doped BNTs exhibited great OER and HER catalytic activity due to the favorable adsorption strength of reaction intermediates. This work sheds light on the design of novel electrocatalysts for water splitting and provides helpful guidelines for the future development of advanced electrocatalysts.

Half-metallicity in smallest cage-like cluster of CdTe with doping of transition metal atoms

We report first principles theory based electronic structure studies of a semiconducting stoichiometric cage-like Cd9Te9 cluster. Substantial changes are observed in the electronic structure of the cluster on passivation with fictitious hydrogen atoms, in particular, widening of the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital and enhancement in stability of cluster is seen. The cluster, when substitutionally mono-doped for a Cd by a set of 3d and 4d transition metal atoms (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh and Pd), is found to acquire polarization as seen from spin resolved density of states near Fermi level. Further, such mono-doping in passivated cluster shows half-metallic behavior. Mapping of partial density of states of each system on that of undoped cluster reveals additional levels caused by doping each TM atom separately. In the 3d elemental doping, Ti and Mn doping result into electron type doping whereas all other cases result into hole doped systems. For all the 4d elements studied, it is akin to the doping with holes for Cd substitution in the outer ring, whereas for Ru and Rh, there is electron type doping in case of substitution for Cd in central ring upon passivation. A comparison of partial density of states plots for bare and passivated clusters, on doping with transition metal atoms, suggests suitability of the cage-like cluster for spintronics applications.

Spin Polarization Properties of Two Dimensional GaP3 Induced by 3d Transition-Metal Doping.

The electronic structure and spin polarization properties of monolayer GaP3 induced by transition metal (TM) doping were investigated through a first-principles calculation based on density functional theory. The calculation results show that all the doped systems perform spin polarization properties, and the Fe–doped system shows the greatest spin polarization property with the biggest magnetic moment. Based on the analysis from the projected density of states, it was found that the new spin electronic states originated from the p–d orbital couplings between TM atoms and GaP3 lead to spin polarization. The spin polarization results were verified by calculating the spin density distributions and the charge transfer. It is effective to introduce the spin polarization in monolayer GaP3 by doping TM atoms, and our work provides theoretical calculation supports for the applications of triphosphide in spintronics.