Variation Of Electronic Structure Research Articles

BiOCl1−xBrx solid solution – Novel synthesis, highly-efficient visible-light-driven photocatalyst, and DFT study

Among various advanced oxidation processes applied in wastewater treatment, photocatalysis has attracted attention in research and industry due to its advantages, such as low cost, high efficiency, and eco-friendliness. With a unique layered structure, bismuth oxyhalides have been widely applied as high-efficiency photocatalysts for organic pollutant degradation in the aqueous environment. However, the large bandgap of BiOCl and the high recombination rate of BiOBr limit their practical application. Tuning bandgap by forming a solid solution is an efficient method to engineer bandgap and prolong the lifetime of photo-induced electron-hole pairs. In this study, a facile solid-state reaction in a vapor chamber was applied to prepared solid solutions of BiOCl1−xBrx. Their photocatalytic performance is significantly improved in comparison with the end components. The optimal composition at x = 0.5 performed degradation efficiencies of 92.3% and 82.6% for rhodamine B and tetracycline degradation, after 70 mins of reaction under light emitting diode (LED) irradiation, respectively. This improvement is attributed to the reduction in bandgap and the effective charge recombination due to the favorable electronic and crystal structure variation, demonstrated by the photoelectrochemical results and density functional theory calculation.

Giant Resistive Switching and Lattice Modulation at Full Temperature Range in a Sr‐Doped Nickelate Oxide Transistor

AbstractHow to promote the resistance switching ratio, enlarge the operating temperature range and accelerate the switching speed is at the forefront of ionic gating electronics. Usually, most attention has been paid to materials with metal‐to‐insulator transition (MIT), e.g., VO2 and SmNiO3. Here, Sr‐doped nickelate (Nd0.8Sr0.2NiO3) films which do not exhibit MIT are used for electric field control of H‐doping and to detect the variation of resistance, lattice, and electronic structures. The experimental results directly show a giant resistive switching by more than 105 at the full temperature range (2 K–300 K) and lattice modulation by 3.4%. More importantly, much faster switching speeds can be achieved in Nd0.8Sr0.2NiO3 devices than in nondoped NdNiO3 ones. Such high switching performance is demonstrated to arise from strongly suppressed Ni–O hybridization after H doping. The results of this study provide a new material paradigm for developing energy‐efficient neuromorphic computing. Further, the doping effect on device performance also suggests a novel approach to develop correlated perovskite oxide transistors in order to fulfill practical applications.

From 8- to 18-Cluster Electrons Superatoms: Evaluation via DFT Calculations of the Ligand-Protected W@Au12(dppm)6 Cluster Displaying Distinctive Electronic and Optical Properties

The iconic W@Au12 icosahedral bare cluster reaches the favorable closed-shell superatomic electron configuration 1S2 1P6 1D10, making it an 18-cluster electron (18-ce) superatom. Here, we pursue the evaluation of a ligand-protected counterpart based on the construction of a fully phosphine-protected [W@Au12(dppm)6] cluster strongly related to the characterized [Au13(dppm)6]5+ homometallic counterpart. The later cluster has the same total number of valence electrons as the former but is considered an 8-ce superatom with 1S2 1P6 configuration. The fundamental differences between 8- and 18-ce species are investigated. The character of the frontier orbitals varies from 1P/1D in the 8-ce case to a 1D/ligand for 18-ce species, enabling an efficient charge transfer toward the ligands upon irradiation, being interesting for electron injection in optoelectronic devices and black absorbers applications. Excited-state properties are also revisited, showing different geometrical and electronic structure variations between 8- and 18-ce species. Moreover, the continuum between the 8- and 18-ce limits has been explored by varying the nature of the encapsulated dopant between group 6 and group 11. The transition between the 8- and 18-ce counts can be formally situated between Pt (8-ce) and Ir (18-ce). Thus, 18-ce derivatives obtained as doped counterparts of homometallic gold clusters can introduce useful alternatives to achieve different properties in related structural motifs, which can be further explored owing to their extension of the well-established versatility of current gold nanoclusters.

Effect of doping concentration on the antiferromagnetic transition temperature of multiferroic YMnO3: A first-principles study

Hexagonal YMnO3 is an attractive multiferroic material whose polarization and magnetic orders are strongly coupled with each other. Doping different cations in hexagonal YMnO3 would influence its properties, especially the magnetic transition temperature (the Néel temperature). In this work, by using first-principles calculations, we not only studied the effects of doping Fe and Cr ions at the Mn-site on the Néel temperature, but also revealed that the variations of electronic structures and the extents of orbital coupling overlaps are both factors to determine the magnetic interaction strength and Néel temperature for YMn1-x(Fe,Cr)xO3 (0 ≤ x < 0.3). Besides the Mn-site, doping rare earth element (La) at the non-magnetic Y-site also influences the Néel temperature. These results are important to provide more understanding about the performance of multiferroic materials.

Monitoring Electron Flow in Nickel Single-Atom Catalysts during Nitrogen Photofixation.

An efficient catalytic system for nitrogen (N2) photofixation generally consists of light-harvesting units, active sites, and an electron-transfer bridge. In order to track photogenerated electron flow between different functional units, it is highly desired to develop in situ characterization techniques with element-specific capability, surface sensitivity, and detection of unoccupied states. In this work, we developed in situ synchrotron radiation soft X-ray absorption spectroscopy (in situ sXAS) to probe the variation of electronic structure for a reaction system during N2 photoreduction. Nickel single-atom and ceria nanoparticle comodified reduced graphene oxide (CeO2/Ni-G) was designed as a model catalyst. In situ sXAS directly reveals the dynamic interfacial charge transfer of photogenerated electrons under illumination and the consequent charge accumulation at the catalytic active sites for N2 activation. This work provides a powerful tool to monitor the electronic structure evolution of active sites under reaction conditions for photocatalysis and beyond.

Lab-Scale X-Ray Emission/Absorption Spectroscopy for Operando Measurement of Electronic Structure of Transition Metals in Battery Electrodes

Tracking the change in electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. X-ray emission spectroscopy (XES) and x-ray absorption fine structure (XAFS) perform this role well with high sensitivity and throughput, but the requisite of synchrotron facilities often limits those availability for material characterization.Using a lab-scale x-ray emission/absorption spectrometer, we investigated the changes in the local structure and chemistry around the 3d transition metal elements of LiMO2 cathodes for Li-ion batteries as a function of the battery state of charge (SoC). Ex situ measurement was prepared from the electrode samples with discrete difference in SoC. Coupled with ex situ measurement, operando measurement was performed using pouch cells with LiMO2 cathode, which enabled a real-time monitoring of chemical shift in an element-specific manner resulted from changing electrode potential.Through the XES mode of the bench-top spectrometer, fluorescence emissions from the LiMO2 cathode, or the cell containing it, was monochromatized by a spherically bent crystal analyzer (SBCA). The Kβ emissions of 3d transition metal elements such as cobalt display position/shape difference of spectrum with varying SoC. The trend of chemical shift and change in spectral features provided the information on the electronic structure variation, such as oxidation state change of 3d transition metals in LiMO2 during charge and discharge (i.e., delithiation and lithiation). Furthermore, valence-to-core (VtC) emission signals helped enable in-depth analysis such as spin structure characterization.In addition to the XES analysis, we could measure K-edge XAFS for the same 3d transition metals in LiMO2 as well. In the XAFS mode of the spectrometer, SBCA monochromatized bremsstrahlung x-ray generated from a high-power x-ray tube is used to make an incident source energy-dispersive. While Kβ XES probed occupied levels, K-edge XAFS examined unoccupied levels providing comprehensive understanding on the change in electronic structure of 3d transition metals in LiMO2. Figure 1

Effect of Disorder and Doping on Electronic Structure and Diffusion Properties of Li3V2O5

V2O5 in its ω phase (Li3V2O5) with excess lithium is a potential alternative to the graphite anode for lithium-ion batteries at low temperature and fast charging conditions owing to its safer voltage (0.6 V vs Li+/Li(s)) and high lithium transport rate. In-operando cationic disorder, as observed in most ordered materials, can produce significant changes in charge compensation mechanisms, anionic activity, lithium diffusion, and operational voltages. In this work, we report the variation in structural distortion, electronic structure, and migration barrier accompanied by disorder using first-principles calculations. Owing to the segregation of lithium atoms in the disordered state, we observe greater distortion, emergence of metallic behavior, and potential anionic activity from nonbonding oxygen states near the Fermi level. Redox capacity can be tuned by doping with 3d metals, which can adjust the participating cationic states, and by fluorine substitution, which can stabilize or suppress anionic states. Moreover, the suppression of anionic activity is found to decrease structural distortion, which is crucial for mitigating voltage fade and hysteresis. Diffusion barrier calculations in the presence of disorder indicate the activation of the remaining 3D paths for lithium hopping which are unavailable in the ordered configuration, explaining its fast-charging ability observed in experiments.

Enhancing oxygen reduction reaction performance in acidic media via bimetal Fe and Cr synergistic effects

Currently, it is a great challenge to improve the stability of Fe-based oxygen reduction reaction (ORR) catalysts in acidic medium, because the Fenton reaction between Fe-based catalyst and H2O2 will reduce the stability of the catalyst. In this study, Fe, Cr and nitrogen-doped carbon (FeCr-N-C) was synthesized via co-impregnation of biomass walnut shells with metal precursor solutions. The FeCr-N-C catalyst has an onset potential of 0.88 V vs. RHE and outperforms the Fe-N-C catalyst in acidic media. Moreover, FeCr-N-C shows negligible activity decay (ΔE1/2 = 14 mV) in 0.1 M HClO4 after 20 000 cycles. The experimental results proved that the bimetal synergism can produce low yield of H2O2 (<2%), which might attribute to variations of local electronic structure. The reactive oxygen species of the catalyst were analyzed by Ultraviolet-visible (UV-Vis) absorption spectra. It was proved that the presence of bimetal inhibited the Fenton reaction between Fe2+/Fe3+ and H2O2, and further improved the stability of the catalysts. Hence, this study proposes an efficient strategy to facilitate the practical application of Fe-based catalysts in acidic media.

First‐principles calculation of mechanical properties and electronic structures of W 4 Co 4− n X n B 4 (X = V, Mn, Fe, Ni; n = 0,1)

The first-principles calculation is performed to explore the mechanical properties and electronic structures of transition elements X (X = V, Mn, Fe, Ni) doped WCoB (tungsten cobalt boron), which has shown high oxidation resistance and melting point under high pressure. The energy analysis indicates that the high pressure leads to the lower lattice constants and less stable structures. The deviation of cohesive energy and formation enthalpy between doped and undoped structures indicates that W4Co3FeB4 and W4Co3NiB4 have similar stability. The high pressure contributes to the increasing of elastic, shear, and bulk moduli, which indicates the increase of covalence. The increase of Poisson's ratio, B/G ratio, and anisotropy index AU indicates the higher ductility and higher anisotropy under high pressure. Based on bulk modulus and shear modulus, the hardness of W4Co4B4, W4Co3FeB4, and W4Co3NiB4 increases under high pressure, which consists of the variation of electronic structures. The density of states (DOS) and partial DOS analysis indicate that the high pressure leads to lower density around Fermi level and higher hybridization. W4Co4B4, W4Co3FeB4, and W4Co3NiB4 show similar variation of mechanical properties, which is determined by the similar atom properties of Co, Fe, and Ni. Similarly, W4Co3VB4 and W4Co3MnB4 also imply similar variation of mechanical properties and electronic structures.

Dual-metal-organic frameworks as ultrahigh-performance bifunctional electrocatalysts for oxygen reduction and oxygen evolution

At present, it is significant to research bifunctional catalysts for metal-air batteries with bargain price, excellent stability, and satisfactory activity. Herein, by density functional theory, the performance of dual-metal-organic frameworks M2-BTC (M2 = Ni2, Fe2, Co2, FeNi, CoNi, FeCo) as bifunctional electrocatalysts to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is investigated. All M2-BTC are proved to possess satisfactory thermodynamical stability. For ORR, FeNi-Ni, Ni2-BTC, Co2-BTC, and CoNi-Ni are confirmed to have high activity with corresponding overpotential of 0.40, 0.25, 0.31, and 0.28 V, respectively, which are both better than Pt(111) (ηORR = 0.45 V). For OER, Fe2-BTC, Ni2-BTC, Co2-BTC, and CoNi-Ni show excellent catalytic activity, with the overpotential of 0.42, 0.38, 0.22, and 0.31 V, respectively, which can be compared to RuO2(110) (ηOER = 0.37 V) or even better than it. According to the ORR/OER potential gap, Ni2-BTC, Co2-BTC, and CoNi-Ni are screened out to be ultrahigh-performance bifunctional electrocatalysts. The results of the highest occupied molecular orbital and the lowest unoccupied molecular orbital confirm that the metal atom is the main active site, and the O atoms attached to the active metal also participate in the reaction. Density of states analysis indicates that the different catalytic performance of M2-BTC is caused by the variety of electronic structures.

In situ optical spectroscopic understanding of electrochemical passivation mechanism on sol–gel processed WO3 photoanodes

A prevailing understanding on electrochemical activation of photoelectrodes is that electrochemical treatment leads to increased charge carrier densities thereby improved photoelectrode performances. Contrary to this understanding, in this study enhanced photoactivity of WO3 photoanode upon electrochemical treatment is ascribed to an extraordinary mechanism of surface trap passivation. The associated mechanism is analyzed by in situ optical spectroscopy, using which the optical property changes of WO3 electrode during electrochemical treatment are monitored. The results suggest surface W5+ species, the origin of surface traps on WO3 photoanodes, are converted to W6+ ions by electrochemical treatment. This study demonstrates the particular ability of the electrochemical strategy to passivate surface traps of photoanodes, and also shows the advantages of in situ optical spectroscopy to investigate the real-time electronic structure variations of electrodes during electrochemical treatment.

Pressure-induced structural transition, metallization, and topological superconductivity in PdSSe

Pressure not only provides a powerful way to tune the crystal structure of transition metal dichalcogenides (TMDCs) but also promotes the discovery of exotic electronic states and intriguing phenomena. Structural transitions from the quasi-two-dimensional layered orthorhombic phase to three-dimensional cubic pyrite phase, metallization, and superconductivity under high pressure have been observed experimentally in TMDCs materials PdS2 and PdSe2. Here, we report a theoretical prediction of the pressure-induced evolutions of crystal structure and electronic structure of PdSSe, an isomorphous intermediate material of the orthorhombic PdS2 and PdSe2. A series of pressure-induced structural phase transitions from the layered orthorhombic structure into an intermediate phase, then to a cubic phase are revealed. The intermediate phase features the same structure symmetry as the ambient orthorhombic phase, except for drastic collapsed interlayer distances and striking changes of the coordination polyhedron. Furthermore, the structural phase transitions are accompanied by electronic structure variations from semiconductor to semimetal, which are attributed to bandwidth broaden and orbital-selective mechanisms. Especially, the cubic phase PdSSe is distinct from the cubic PdS2 and PdSe2 materials by breaking inversion and mirror-plane symmetries, but showing similar superconductivity under high pressure, which is originated from strong electron-phonon coupling interactions concomitant with topologically nontrivial Weyl and high-fold Fermions. The intricate interplay between lattice, charge, and orbital degrees of freedom as well as the topologically nontrivial states in these compounds will further stimulate wide interest to explore the exotic physics of the TMDCs materials.

Tuning Mixed Electronic/Ionic Conductivity of 2D CdPS3 Nanosheets as an Anode Material by Synergistic Intercalation and Vacancy Engineering

AbstractMetal phosphorus trichalcogenides (MPTCs) are structurally adjustable 2D layered materials with unique electronic structures and high chemical diversity, implying the huge potential for energy storage application. In the typical electrochemical reaction process, rapid electron/ion conduction and abundant ion transport channels are the key parameters that influence the overall electrochemical performance of the electrode materials. Herein, 2D Cd1−xPS3Li2x nanosheets with enhanced mixed electronic/ionic conductivity are synthesized by the intercalation and vacancy strategy. The as‐prepared thin‐layered Cd1−xPS3Li2x electrode delivers high capacities of 1056 mAh g−1 at 0.2 A g−1 and 678 mAh g−1 at 8 A g−1, when used as anode in lithium‐ion batteries. The variation of electronic structure and spatial layered structure in Cd1−xPS3Li2x induced by the synergistic effect of lithium‐ion intercalation and Cd vacancies promote the dynamics of mixed electron/ion transport and offer more ion diffusion pathways, resulting in its excellent electrochemical performance. The strategy of mixed electron/ion conduction tuning for Cd1−xPS3Li2x can be extended to other MPTCs compounds to further develop their potential in the field of energy storage.

The interplay between acid-base properties and Fermi level pinning of a nano dispersed tungsten oxide - titania catalytic system

A series of WO3/TiO2 catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH3. Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO3 and TiO2 and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO3/TiO2 interface were quantified using variations in the system's electronic structure. Altering the dispersion and size of the WO3 nanostructures results to drastic changes in titania's surface electron distribution, which are reflected in the pinning of Fermi level through an electron transfer process between WO3 and TiO2. The variations in the Fermi level were further related to changes in the point of zero charge (PZC) values and the activity towards NO SCR with NH3, which was used as a test reaction. Temperature Programmed Surface Reaction (TPSR) was employed to study the catalytic activity at temperatures ranging from 30 °C to 500 °C and was quantitatively correlated to changes in coverage and interfacial charge transfer. We demonstrate that higher WO3 loading on TiO2 results in a stronger electronic interaction and a higher catalytic activity. This is because electron transfer increases the surface electron density, which enhances the surface basicity of TiO2. The concomitant decrease in the adsorption energy of NH3 results in a decrease in the activation energy, which is reflected in the SCR temperature onset.

Organic single crystals of charge-transfer complexes: model systems for the study of donor/acceptor interactions.

The charge-transfer (CT) state arising as a hybrid electronic state at the interface between charge donor and charge acceptor molecular units is important to a wide variety of physical processes in organic semiconductor devices. The exact nature of this state depends heavily on the nature and co-facial overlap between the donor and acceptor; however, altering this overlap is usually accompanied by extensive confounding variations in properties due to extrinsic factors, such as microstructure. As a consequence, establishing reliable relationships between donor/acceptor molecular structures, their molecular overlap, degree of charge transfer and physical properties, is challenging. Herein, we examine the electronic structure of a polymorphic system based on the donor dibenzotetrathiafulvalene (DBTTF) and the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in the form of high-quality single crystals varying in the donor-acceptor overlap. Using angle-resolved photoemission spectroscopy, we resolve the highest occupied molecular orbital states of the CT crystals. Analysis based on field-effect transistors allows us to probe the sub-gap states impacting hole and electron transport. Our results expand the understanding on the impact of donor and acceptor interactions on electronic structure and charge transport.

Morphology, thermal stability, electronic structure and mechanical properties of α-AlFeMnSi phases with varying Mn/Fe atomic ratios: Experimental studies and DFT calculations

Separation of Fe-containing intermetallics is an effective method to decrease Fe content in Al-Si alloys. The three-dimensional (3D) morphology and stability of Fe-containing intermetallics are important parameters affecting their separation efficiency. Combined with experiments and first-principles calculations, the variation of 3D morphology, stability, electronic structure and mechanical properties of α-AlFeMnSi are studied with the evolution of Fe/Mn atomic ratio. The experimental results show that the 3D morphology of α-AlFeMnSi transforms from Chinese character to regular polyhedron with the increment of Mn/Fe atomic ratio and all α-AlFeMnSi phases have cubic crystal structure. The calculated mixing enthalpies indicate that all α-AlFeMnSi phases are stable in thermodynamics due to the negative values. The electronic structure and Mulliken population calculations show that the variation of Mn/Fe ratio results in the overall change of chemical bondings of Si-Mn, Si-Fe, Al-Mn and Al-Fe, which leading to the evolution of stability and mechanical properties of α-AlFeMnSi phases. The calculated results of mechanical properties demonstrate that the Young’s modulus and hardness of α-AlFeMnSi phases are improved with the increment of Mn/Fe atomic ratio, which is also validated by nano-indentation measurements. These results provide the componential guidance about designing easy-separable Fe-containing intermetallics and try to explain physical mechanism of property evolution of α-AlFeMnSi phase.

CHARMM‐GUI Drude prepper for molecular dynamics simulation using the classical Drude polarizable force field

Explicit treatment of electronic polarizability in empirical force fields (FFs) represents an extension over a traditional additive or pairwise FF and provides a more realistic model of the variations in electronic structure in condensed phase, macromolecular simulations. To facilitate utilization of the polarizable FF based on the classical Drude oscillator model, Drude Prepper has been developed in CHARMM-GUI. Drude Prepper ingests additive CHARMM protein structures file (PSF) and pre-equilibrated coordinates in CHARMM, PDB, or NAMD format, from which the molecular components of the system are identified. These include all residues and patches connecting those residues along with water, ions, and other solute molecules. This information is then used to construct the Drude FF-based PSF using molecular generation capabilities in CHARMM, followed by minimization and equilibration. In addition, inputs are generated for molecular dynamics (MD) simulations using CHARMM, GROMACS, NAMD, and OpenMM. Validation of the Drude Prepper protocol and inputs is performed through conversion and MD simulations of various heterogeneous systems that include proteins, nucleic acids, lipids, polysaccharides, and atomic ions using the aforementioned simulation packages. Stable simulations are obtained in all studied systems, including 5 μs simulation of ubiquitin, verifying the integrity of the generated Drude PSFs. In addition, the ability of the Drude FF to model variations in electronic structure is shown through dipole moment analysis in selected systems. The capabilities and availability of Drude Prepper in CHARMM-GUI is anticipated to greatly facilitate the application of the Drude FF to a range of condensed phase, macromolecular systems.

The influence of LiH and TiH2 on hydrogen storage in MgB2 I: Promotion of bulk hydrogenation at reduced temperature

Mg(BH4)2 is an attractive hydrogen storage material, owing to its high gravimetric capacity of 14.9 wt %. However, the dehydrogenated material MgB2 is very difficult to rehydrogenate, requiring excessive pressures and temperatures. Here we report the influence of LiH and TiH2 on hydrogen storage reactions involving Bulk MgB2 using XRD, XAS, FTIR and NMR. In ball-milled mixtures of LiH/MgB2, the LiH loses crystallinity but remains undissociated, forming a weakly bound complex with MgB2. The weak interactions produce minor variations in the local electronic structure at B and Mg, but do not markedly affect the underlying MgB2 hexagonal crystal structure. No evidence is found for a mixed-metal boride Mg1-xLixB2 in the as-prepared LiH/MgB2 materials. The presence of LiH dramatically improves the hydrogenation of MgB2 at 700 bar, forming borohydride 100 °C below the minimum hydrogenation temperature of pure MgB2 and without the formation of undesirable intermediates such as [B3H8]-, [B10H10]2- or [B12H12]2-. Evidence is reported for a mixed-metal borohydride of the type Mg(3-x)/2Lix(BH4)3 produced by the hydrogenation. Subsequent desorption is also improved compared to pure Mg(BH4)2 and LiBH4, showing single-step hydrogen release up to ∼8 wt% by 380 °C, whereas Mg(BH4)2 and LiBH4 still retain significant amounts of hydrogen at this temperature. The material produced by desorption contains both MgB2 and Mg metal, revealing the original LiH/MgB2 system is not fully reversible. In contrast to LiH, TiH2 is essentially inert when ball-milled with MgB2, and high-pressure hydrogenation leaves only unreacted TiH2 and MgB2. Thus, added TiH2 provides no benefit to MgB2 hydrogenation.

Electronic Structure and Stacking Arrangement of Tungsten Disulfide at the Gold Contact.

There is an intensive effort to control the nature of attractive interactions between ultrathin semiconductors and metals and to understand its impact on the electronic properties at the junction. Here, we present a photoelectron spectroscopy study on the interface between WS2 films and gold, with a focus on the occupied electronic states near the Brillouin zone center (i.e., the Γ point). To delineate the spectra of WS2 supported on crystalline Au from the suspended WS2, we employ a microscopy approach and a tailored sample structure, in which the WS2/Au junction forms a semi-epitaxial relationship and is adjacent to suspended WS2 regions. The photoelectron spectra, as a function of WS2 thickness, display the expected splitting of the highest occupied states at the Γ point. In multilayer WS2, we discovered variations in the electronic states that spatially align with the crystalline grains of underlying Au. Corroborated by density functional theory calculations, we attribute the electronic structure variations to stacking variations within the WS2 films. We propose that strong interactions exerted by Au grains cause slippage of the interfacing WS2 layer with respect to the rest of the WS2 film. Our findings illustrate that the electronic properties of transition metal dichalcogenides, and more generally 2D layered materials, are physically altered by the interactions with the interfacing materials, in addition to the electron screening and defects that have been widely considered.

Insight into the Improvement Effect of Nitrogen Dopant in Ag/Co3O4 Nanocubes for Soot Oxidation: Experimental and Theoretical Studies

Different doping amounts of N-doped Ag/Co3O4 nanocubes were synthesized for the first time for catalytic soot oxidation. The N-doped sample exhibited remarkably improved catalytic activity, of which the maximum decrease in temperature for 90% soot conversion was almost 40 ℃. Characterization results analyzed by TEM, XPS, EPR, H2-TPR, O2-TPD, etc. revealed that the incorporation of N atoms can alter the electronic structure, leading to the generation of more oxygen vacancies and enhancement of lattice oxygen mobility. Meanwhile, larger surface area, rugged morphology and promoted reducibility also contribute to the performance improvement. DFT calculations on the differential charge density, Gibbs free energy, etc. were performed to investigate the intrinsic reasons on an atomic level. Due to the relatively higher electronegativity, N dopant could be an electron-appealing center to promote efficient electron transfer, resulting in the redistribution of charge density and formation of conductive Co–N bonds. This variation in electronic structure favors lowering the formation energy of oxygen vacancies and facilitating the activation of the lattice oxygen originated from the highly hybridized Co–O bonds, which ultimately reduces the activation barriers for reactants/intermediates and accelerates the reaction kinetics. This study evidenced that N doping could be an effective strategy to promote catalytic soot oxidation.