Highly efficient MoS2/WS2 heterojunctions for the CO2 reduction reaction: strong electronic transmission.

Transition metal dichalcogenides (TMDs) possess several advantages, such as high conductivity, stable structure, and low cost, making them promising catalysts for carbon dioxide electroreduction. However, the high overpotential and the desorption characteristics of the reaction products during the reduction of carbon dioxide present significant challenges in the field of catalysis. In this study, we have further enhanced the catalytic activity of the original WS2 structure by constructing a heterojunction. We systematically investigate the catalytic activity of MoS2/WS2 heterojunctions supported by transition metals using density functional theory (DFT) calculations. The findings of this study are as follows: (1) the unique multiphase structure enhances the catalytic performance for CO2 reduction. (2) After constructing the MoS2/WS2 heterojunction, the electronic properties and conductivity of the heterojunction can be significantly enhanced, thereby facilitating the catalytic reduction of carbon dioxide. The Cu loading on the Cu@MoS2/WS2 heterojunction significantly reduces the overpotential, with a very low limit potential of -0.58 V. The adsorption behavior of CO on the Cu@MoS2/WS2 heterojunction was evaluated using adsorption energy, desorption energy, and density of states (DOS). The appropriate interaction between CO and Cu@ MoS2/WS2 promotes the reduction of CO2 to CO and facilitates smooth desorption of CO, demonstrating a strong catalytic effect on the CO2 reduction reaction (CO2RR). Therefore, it can be seen that Cu@MoS2/WS2 may be considered as potential single-atom catalysts (SACs) for CO2 reduction electrocatalysts. Finally, it is hoped that our results will provide theoretical support for the development of efficient CO2 reduction catalysts.

Controlling the magnetic anisotropy of RumIrn (m + n = 3) clusters using the MgO(001) substrate.

Large perpendicular magnetic anisotropy energy (MAE) and flexible regulation of the magnitude and direction of MAE have great potential for application in information storage devices. Here, utilizing first-principles calculations, we investigated the magnetic properties of free and MgO(001) supported RumIrn clusters (RumIrn@MgO(m + n = 3)). The results indicate that the MAE of mixed clusters increases with the number of Ir atoms due to Ir having a strong coupling between the non-degenerate dxy and dx2-y2 states. The MAE of free Ir3 is -8.18 meV with the easy magnetization direction parallel to the x-axis, while the MAE of supported Ir3 on the MgO substrate increases by a factor of 2.6, and the easy magnetization axis of the structure is shifted to a direction perpendicular to the substrate surface. This change in MAE is due to the significant enhancement in the coupling between the non-degenerate dyz and dx2-y2 states near the Fermi level of Ir3 atoms. Moreover, Ir3@MgO possesses high thermodynamic stability. These results give a new method for manipulating MAE and the direction of easy magnetization, which has great potential for application in magnetic nanodevices.

A molecular device providing a remarkable spin filtering effect due to the central molecular stretch caused by lateral zigzag graphene nanoribbon electrodes.

Through the density functional theory, we studied molecular devices composed of single tetrathiafulvalene (TTF) molecules connected with zigzag graphene nanoribbon electrodes by four different junctions. Interestingly, some devices have exhibited half-metallic behavior and can bring out a perfect spin filtering effect and remarkable negative differential resistance behavior. The current-voltage characteristics show that these four devices possess different spin current values. We found that all the TTF molecules were stretched due to interactions with the electrodes in the four devices. This leads to the Fermi levels of the three devices being down-shifted to the valence band; therefore, these devices exhibit half-metallic properties. The underlying mechanisms of the different spin current values are attributed to the different electron transmission pathways (via chemical bonds or through hopping between atoms). These results suggest that the device properties and conductance are controlled by different junctions. Our work predicts an effective way for designing high-performance spin-injected molecular devices.

Transition of recollision trajectories from linear to elliptical polarization.

Using a classical ensemble method, we revisit the topic of recollision and nonsequential double ionization with elliptically polarized laser fields. We focus on how the recollision mechanism transitions from short trajectories with linear polarization to long trajectories with elliptical polarization. We propose how this transition can be observed by meansuring the carrier-envelop-phase dependence of the correlated electron momentum spectra using currently available few-cycle laser pulses.

Electric field control of the magnetic anisotropy energy of double-vacancy graphene decorated by iridium atoms.

To solve the fundamental dilemma in data storage applications, it is crucial to manipulate the magnetic anisotropy energy (MAE). Herein, using first-principles calculations, we predict that the system of double-vacancy graphene decorated by iridium atoms possesses high stability, giant MAE, perpendicular-anisotropy and long-range ferromagnetic coupling. More importantly, the amplitude of MAE can be manipulated by electric fields. This is due to the change in the occupation number of Ir-5d orbitals. The present hybrid system could be a high-performance nanoscale information storage device with ultralow energy consumption.

First-principles prediction of magnetic superatoms in 4d-transition-metal-doped magnesium clusters.

We theoretically predict magnetic superatoms in the 4d-transition-metal-doped Mg8 clusters using a spin-polarized density functional theory method. We demonstrate that TcMg8 is highly energetically stable in both structure and magnetic states, and identify it as a magnetic superatom with a magnetic moment as large as 5 µB. The magnetic TcMg8 with 23 valence electrons has a configuration of 1S(2)1P(6)1D(10) closed shell and 2S(1)2D(4) open shell, complying with Hund's rule similar to the single atom. We elucidate the formation mechanism of the magnetic TcMg8 superatom based on the detailed analysis of molecular orbitals, and attribute it to the large exchange interaction and moderate crystal field effect. Finally, we predict that the magnetic TcMg8 may exhibit semiconductor-like property with spin polarization characteristics.

Enhanced Power Factor and Ultralow Lattice Thermal Conductivity Induced High Thermoelectric Performance of BiCuTeO/BiCuSeO Superlattice.

Based on the first-principles calculations, the electronic structure and transport properties of BiMChO (M=Cu and Ag, Ch=S, Se, and Te) superlattices have been studied. They are all semiconductors with indirect band gaps. The increased band gap and decreased band dispersion near the valence band maximum (VBM) lead to the lowest electrical conductivity and the lowest power factor for p-type BiAgSeO/BiCuSeO. The band gap value of BiCuTeO/BiCuSeO decreases because of the up-shifted Fermi level of BiCuTeO compared with BiCuSeO, which would lead to relatively high electrical conductivity. The converged bands near VBM can produce a large effective mass of density of states (DOS) without explicitly reducing the mobility µ for p-type BiCuTeO/BiCuSeO, which means a relatively large Seebeck coefficient. Therefore, the power factor increases by 15% compared with BiCuSeO. The up-shifted Fermi level leading to the band structure near VBM is dominated by BiCuTeO for the BiCuTeO/BiCuSeO superlattice. The similar crystal structures bring out the converged bands near VBM along the high symmetry points Γ-X and Z-R. Further studies show that BiCuTeO/BiCuSeO possesses the lowest lattice thermal conductivity among all the superlattices. These result in the ZT value of p-type BiCuTeO/BiCuSeO increasing by over 2 times compared with BiCuSeO at 700 K.

Engineering Magnetic Anisotropy of Rhenium Atom in Nitrogenized Divacancy of Graphene.

The effects of charging on the magnetic anisotropy energy (MAE) of rhenium atom in nitrogenized-divacancy graphene (Re@NDV) are investigated using density functional theory (DFT) calculations. High-stability and large MAE of 71.2 meV are found in Re@NDV. The more exciting finding is that the magnitude of MAE of a system can be tuned by charge injection. Moreover, the easy magnetization direction of a system may also be controlled by charge injection. The controllable MAE of a system is attributed to the critical variation in dz2 and dyz of Re under charge injection. Our results show that Re@NDV is very promising in high-performance magnetic storage and spintronics devices.

Graphdiyne-supported single-cluster electrocatalysts for highly efficient carbon dioxide reduction reaction.

The electrochemical CO2 reduction reaction (CO2RR) has become a promising technology to resolve globally accelerating CO2 emissions and produce chemical fuels. In this work, the electrocatalytic performance of transition metal (TM = Cu, Cr, Mn, Co, Ni, Mo, Pt, Rh, Ru and V) triatomic clusters embedded in a graphdiyne (GDY) monolayer (TM3@GDY) for CO2RR is investigated by density functional theory (DFT) calculations. The results indicate that Cr3@GDY possesses the best catalytic performance with a remarkably low rate-limiting step of 0.39 eV toward the CO2 product, and it can also effectively suppress the hydrogen evolution reaction (HER) during the entire CO2RR process. Studies on the rate-limiting steps (CHO* + H+ + e- → CHOH) of Crn@GDY (n = 1-4) structures demonstrate that the high catalytic performance is attributed to the strong synergistic reaction of three Cr atoms interacting with the C atom for the Cr3@GDY structure. The strong synergistic reaction gives rise to the weakest interaction between O-Cr atoms, which leads to the strongest interaction between O-H atoms and makes the hydrogenation process easier for the Cr3@GDY structure. Furthermore, ab initio molecular dynamics simulations (AIMD) at 500 K reveal the high thermodynamic stability of the Cr3@GDY structure. These studies may provide a new approach for designing highly efficient electrocatalysts for the CO2RR under ambient conditions.

Termination effects of single-atom decorated v-Mo2CTx MXene for the electrochemical nitrogen reduction reaction.

The lack of the green, economical and high-efficient catalysts restrict the development of electrochemical nitrogen reduction reaction (NRR). By means of density functional theory (DFT) calculations, we have systematically investigated the NRR catalytic performance of single atoms decorated v-Mo2CT2 (T = O, F, OH, Cl, and Li) MXene (TM@v-Mo2CT2). Our calculation results reveal the introduction of single atom can significantly improve the NRR activity and selectivity on v-Mo2CO2, and Ir@v-Mo2CO2 system possesses the lowest limiting potential of only -0.33 V among all studied systems. The termination effects of TM@v-Mo2CT2 are further discussed and a descriptor of the adsorption energy of *NNH species (ΔE(*NNH)) is proposed to establish the relationship with NRR limiting potential (UL(NRR)), in which a moderate (ΔE(*NNH)) is required for high NRR activity. Moreover, a good linear relationship between the ΔE(*NNH) and the excess electrons on Ir atom shows that different ΔE(*NNH) originates from the difference of valence state of Ir atom, which is due to the change of coordination environment. Importantly, the synergistic effects of Ir atom and the surface O-terminations during the first hydrogenation step lead to a promoted NRR performance. Our study might provide new possibilities for rational design of cost-effective MXene-based NRR electrocatalysts.

Giant magnetic moment of the core-shell Co13@Mn20 clusters: first-principles calculations.

The core-shell clusters Co(13)@TM(20) with TM = Mn, Fe, Co, and Ni are investigated within first-principles simulations in the framework of density-functional theory. Huge magnetic moments have been found in the Co(13)@TM(20) clusters especially for the Co(13)@Mn(20) cluster with a giant magnetic moment of 113 µ(B). The large magnetic moments are mainly due to the special core-shell structure and the weak interaction between the TM and other atoms.

A DFT screening of single transition atoms supported on MoS2 as highly efficient electrocatalysts for the nitrogen reduction reaction.

The development of low-cost and highly efficient materials for the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is an attractive and challenging topic in chemistry. In this study, the electrocatalytic performance of a series of transition metal (TM) atoms supported on MoS2 nanosheets (TM@MoS2) was systematically investigated using density functional theory (DFT) calculations. It was found that Re supported on MoS2 (Re@MoS2) has the best NRR catalytic activity with a limiting potential of -0.43 V, along with high selectivity over the competing hydrogen evolution reaction (HER). Moreover, the ab initio molecular dynamics (AIMD) simulations at 500 K and density of states (DOS) calculations indicated the high thermodynamic stability and excellent electrical conductivity of Re@MoS2. A linear trend between several parameters of single atom catalysts (SACs) and the adsorption Gibbs free energy change of the NH species (ΔG*NH) was observed, indicating the later as a simple descriptor for the facilitated screening of novel SACs. These results pave the way for exploring novel, highly efficient electrocatalysts for the electrochemical NRR under ambient conditions.

DBD Plasma Combined with Different Foam Metal Electrodes for CO2 Decomposition: Experimental Results and DFT Validations.

In the last few years, due to the large amount of greenhouse gas emissions causing environmental issue like global warming, methods for the full consumption and utilization of greenhouse gases such as carbon dioxide (CO2) have attracted great attention. In this study, a packed-bed dielectric barrier discharge (DBD) coaxial reactor has been developed and applied to split CO2 into industrial fuel carbon monoxide (CO). Different packing materials (foam Fe, Al, and Ti) were placed into the discharge gap of the DBD reactor, and then CO2 conversion was investigated. The effects of power, flow velocity, and other discharge characteristics of CO2 conversion were studied to understand the influence of the filling catalysts on CO2 splitting. Experimental results showed that the filling of foam metals in the reactor caused changes in discharge characteristics and discharge patterns, from the original filamentary discharge to the current filamentary discharge as well as surface discharge. Compared with the maximum CO2 conversion of 21.15% and energy efficiency of 3.92% in the reaction tube without the foam metal materials, a maximum CO2 decomposition rate of 44.84%, 44.02%, and 46.61% and energy efficiency of 6.86%, 6.19%, and 8.85% were obtained in the reaction tubes packed with foam Fe, Al, and Ti, respectively. The CO2 conversion rate for reaction tubes filled with the foam metal materials was clearly enhanced compared to the non-packed tubes. It could be seen that the foam Ti had the best CO2 decomposition rate among the three foam metals. Furthermore, we used density functional theory to further verify the experimental results. The results indicated that CO2 adsorption had a lower activation energy barrier on the foam Ti surface. The theoretical calculation was consistent with the experimental results, which better explain the mechanism of CO2 decomposition.

Exploration of Highly Efficient Blue-Violet Light Conversion Agents for an Agricultural Film Based on Structure Optimization of Triphenylacrylonitrile.

To obtain highly efficient blue-violet light conversion agents used for an agricultural film, six triarylacrylonitrile derivatives and their doping films were prepared. Further, the luminogens have the ability to convert ultraviolet light into blue-violet light and exhibit aggregation-dependent fluorescence emission and high-contrast fluorescence quantum yields from 0.004 to 0.833. On the basis of X-ray single-crystal diffraction analysis and aggregation-induced emission activity tests, the variant fluorescence quantum yields are attributed to intermolecular π-π stacking and phase transition between the crystalline state and amorphous state. In a simulated greenhouse environment, the luminogens exhibit excellent photostability. However, their fluorescence intensity drops to 17-40% of the prime intensity after outdoor radiation for 1 month as a result of the ring-closing oxidation reaction (in the summer). By comprehensively considering the above photophysical properties and mechanical properties of the doping film, 2-([1,1'-biphenyl]-4-yl)-3,3-diphenylacrylonitrile is a potential light conversion agent for an agricultural film in the winter. More importantly, the results indicate that the properties of the light conversion films are expected to be further improved by molecular design, inhibiting the ring-closing oxidation reaction and dispersion of crystalline nanoparticles in the doping film.

Structure and magnetic properties of icosahedral PdxAg13-x (x = 0-13) clusters.

In this article, we present a modified Velocity-Verlet algorithm that makes cluster system converge rapidly and accurately. By combining it with molecular dynamics simulations, we develop an effective global sampling method for extracting isomers of bimetallic clusters. Using this method, we obtain the isomers of icosahedral PdxAg13-x (x = 0-13). Additionally, using the first-principle spin-polarized density functional theory approach, we find that each isomer still retains its icosahedral structure because of strong s-d orbital hybridization, and the cluster is more stable when a Pd atom is at the center of the cluster. With increasing x value, the magnetic moment decreases linearly from 5.0 µB at x = 0, until reaching zero at x = 5, and then increases linearly up to 8.0 µB at x = 13. By calculating the atom-projected density of states (PDOS), we reveal that the magnetic moment of PdxAg13-x mainly originates from s electrons of Ag when 0 ≤ x < 5, and d electrons of Pd when 5 < x ≤ 13. The PDOS results also show that the PdxAg13-x tends to transform from a semiconductor state to semi-metallic state when x gradually increases from 0 to 13.

High-temperature quantum anomalous Hall effect in honeycomb bilayer consisting of Au atoms and single-vacancy graphene.

The quantum anomalous Hall effect (QAHE) is predicted to be realized at high temperature in a honeycomb bilayer consisting of Au atoms and single-vacancy graphene (Au2-SVG) based on the first-principles calculations. We demonstrate that the ferromagnetic state in the Au2-SVG can be maintained up to 380 K. The combination of spatial inversion symmetry and the strong SOC introduced by the Au atoms causes a topologically nontrivial band gap as large as 36 meV and a QAHE state with Chern number C = -2. The analysis of the binding energy proved that the honeycomb bilayer is stable and feasible to be fabricated in experiment. The QAHEs in Ta2-SVG and other TM2-SVGs are also discussed.

Reversible switching of magnetic states by electric fields in nitrogenized-divacancies graphene decorated by tungsten atoms.

Magnetic graphene-based materials have shown great potential for developing high-performance electronic devices at sub-nanometer such as spintronic data storage units. However, a significant reduction of power consumption and great improvement of structural stability are needed before they can be used for actual applications. Based on the first-principles calculations, here we demonstrate that the interaction between tungsten atoms and nitrogenized-divacancies (NDVs) in the hybrid W@NDV-graphene can lead to high stability and large magnetic anisotropy energy (MAE). More importantly, reversible switching between different magnetic states can be implemented by tuning the MAE under different electric fields, and very low energy is consumed during the switching. Such controllable switching of magnetic states is ascribed to the competition between the tensile stain and orbital magnetic anisotropy, which originates from the change in the occupation number of W-5d orbitals under the electric fields. Our results provide a promising avenue for developing high-density magnetic storage units or multi-state logical switching devices with ultralow power at sub-nanometer.