Redistribution Of Charge Density Research Articles

Unveiling the Structure of Metal–Nanodiamonds Bonds: Experiment and Theory

In this study, we conducted a theoretical simulation to compare the effects of various factors on the atomic and electronic structures and the magnetic properties of copper and gadolinium ions bonded to carboxylated species of (111) diamond surfaces. It was experimentally found that in the temperature range above 120 K, the magnetic moments of chelated Gd3+ and Cu2+ equal 6.73 and 0.981 Bohr magnetons, respectively. In the temperature range from 12 to 2 K, these magnetic moments sharply decrease to 6.38 and 0.88 Bohr magnetons. Specifically, we examined the effects of the number of covalent adatom–diamond substrate bridges, coordination of water molecules, and shallow carbon-inherited spins in the substrate on the physical properties of the metal center. Our simulation predicted that increasing the number of bonds between the chelated metal ion and substrate while decreasing the number of coordinating water molecules corresponded to a decrease in the magnetic moment of metal ions in a metal–diamond system. This is due to the redistribution of the electron charge density in an asymmetric metal–diamond system. By comparing our theoretical results with experimental data, we proposed configurations involving one and, in a minor number of cases, two surface –COO− groups and maximum coordination of water molecules as the most realistic options for Cu- and Gd-complexes.

Unveiling Mechanistic Insight into Accelerating Oxygen Molecule Activation by Oxygen Defects in Co3O4-x/g-C3N4 p-n Heterojunction for Efficient Photo-Assisted Uranium Extraction from Seawater.

Photo-assisted uranium extraction from seawater (UES) is regarded as an efficient technique for uranium resource recovery, yet it currently faces many challenges, such as issues like biofouling resistance, low charge separation efficiency, slow carrier transfer, and a lack of active sites. Based on addressing the above challenges, a novel oxygen-deficient Co3O4-x/g-C3N4 p-n heterojunction is developed for efficient photo-assisted uranium extraction from seawater. Relying on the defect-coupling heterojunction synergistic effect, the redistribution of molecular charge density formed the built-in electric field as revealed by DFT calculations, significantly enhancing the separation efficiency of carriers and accelerating their migration rate. Notably, oxygen vacancies served as capture sites for oxygen, effectively promoting the generation of reactive oxygen species (ROS), thereby significantly improving the photo-assisted uranium extraction performance and antibacterial activity. Thus, under simulated sunlight irradiation with no sacrificial reagent added, Co3O4-x/g-C3N4 extracted a high uranium extraction amount of 1.08mgg-1 from 25 L of natural seawater after 7 days, which is superior to most reported carbon nitride-based photocatalysts. This study elaborates on the important role of surface defects and inerface engineering strategies in enhancing photocatalytic performance, providing a new approach to the development and design of uranium extraction material from seawater.

Unveiling Mechanistic Insight into Accelerating Oxygen Molecule Activation by Oxygen Defects in Co3O4-x/g-C3N4 p-n Heterojunction for Efficient Photo-Assisted Uranium Extraction from Seawater.

Photo-assisted uranium extraction from seawater (UES) is regarded as an efficient technique for uranium resource recovery, yet it currently faces many challenges, such as issues like biofouling resistance, low charge separation efficiency, slow carrier transfer, and a lack of active sites. Based on addressing the above challenges, a novel oxygen-deficient Co3O4-x/g-C3N4 p-n heterojunction is developed for efficient photo-assisted uranium extraction from seawater. Relying on the defect-coupling heterojunction synergistic effect, the redistribution of molecular charge density formed the built-in electric field as revealed by DFT calculations, significantly enhancing the separation efficiency of carriers and accelerating their migration rate. Notably, oxygen vacancies served as capture sites for oxygen, effectively promoting the generation of reactive oxygen species (ROS), thereby significantly improving the photo-assisted uranium extraction performance and antibacterial activity. Thus, under simulated sunlight irradiation with no sacrificial reagent added, Co3O4-x/g-C3N4 extracted a high uranium extraction amount of 1.08mgg-1 from 25 L of natural seawater after 7 days, which is superior to most reported carbon nitride-based photocatalysts. This study elaborates on the important role of surface defects and inerface engineering strategies in enhancing photocatalytic performance, providing a new approach to the development and design of uranium extraction material from seawater.

Solar enhanced oxygen evolution reaction with transition metal telluride.

The photo-enhanced electrocatalytic method of oxygen evolution reaction (OER) shows promise for enhancing the effectiveness of clear energy generation through water splitting by using renewable and sustainable source of energy. However, despite benefits of photoelectrocatalytic (PEC) water splitting, its uses are constrained by its low efficiency as a result of charge carrier recombination, a large overpotential, and sluggish reaction kinetics. Here, we illustrate that Nickel telluride (NiTe) synthesized by hydrothermal methods can function as an extremely effective photo-coupled electrochemical oxygen evolution reaction (POER) catalyst. In this study, NiTe was synthesized by hydrothermal method at 145°C within just an hour of reaction time. In dark conditions, the NiTe deposited on carbon cloth substrate shows a small oxygen evolution reaction overpotential (261mV) at a current density of 10mA cm-2, a reduced Tafel slope (65.4mV dec-1), and negligible activity decay after 12h of chronoamperometry. By virtue of its enhanced photo response, excellent light harvesting ability, and increased interfacial kinetics of charge separation, the NiTe electrode under simulated solar illumination displays exceptional photoelectrochemical performance exhibiting overpotential of 165mV at current density of 10mA cm-2, which is about 96mV less than on dark conditions. In addition, Density Functional Theory investigations have been carried out on the NiTe surface, the results of which demonstrated a greater adsorption energy for intermediate -OH on the catalyst site. Since the -OH adsorption on the catalyst site correlates to catalyst activation, it indicates the facile electrocatalytic activity of NiTe owing to favorable catalyst activation. DFT calculations also revealed the facile charge density redistribution following intermediate -OH adsorption on the NiTe surface. This work demonstrates that arrays of NiTe elongated nanostructure are a promising option for both electrochemical and photoelectrocatalytic water oxidation and offers broad suggestions for developing effective PEC devices.

Adsorption of alkaline metals (Li, Na, K) on armchair silicene nanoribbons

The paper presents the results of studies of structural, electronic and magnetic properties of amrchair silicene nanoribbons (ASiNR) atomic systems adsorbing alkaline atoms (ASiNR-Li, ASiNR-Na, ASiNR-K). The results are calculated based on density function theory (DFT) and through a VASP simulation package. Some basic characteristics have been investigated such as: optimal adsorption position, electron band structures, density of states, charge density distribution, charge density difference, and spin density distribution. The results show that the hollow adsorption site is optimal. After adsorption, the system structure has changes in bond edge length and buckling. Adsorption systems do not exist band gap, exhibiting typical metallic properties. Alkaline adsorption leads to a redistribution of charge density; causes a strong charge shift compared to the pristine system, and also leads to a change in the magnetic moment of the structure.

Electric-field-driven ferromagnetic response in Janus MnReX3 (X = Se, S) monolayer via asymmetric interface orbital hybridization

Abstract Regulating spin-related electronic structures of two dimensional (2D) materials by an external electric field plays a substantial role in achieving spintronic and multistate information storage. However, electric-field-dependent ferromagnetic behavior at atomic-thick 2D materials is very difficult to be realized due to their intrinsic inversion symmetry, in which the symmetric spatial distribution of charge density makes it become insensitive to spontaneous polarization from external electric field. Herein, a new-type Janus MnReX3 (X = Se, S) monolayer with noncentrosymmetric configuration in which their orbital hybridization at internal interface can be engineered by rearranging the spatial symmetry of out-of-plane charge density. As a result, the spin exchange interaction among magnetic sites can be regulated by the electric-field-driven charge density redistribution, leading to a controllable ferromagnetic behavior at room temperature. Our results not only suggest a promising strategy to regulate the ferromagnetic response by reducing the crystal symmetry, but also provide a new insight into designing 2D magnetic materials.

Robustness of frictional anisotropy under high load due to self-folding

Friction anisotropy is not only related to macroscopic natural phenomena, but also closely involves the emerging field of nanotechnology. The previous strategies to achieve friction anisotropy requires delicate adjustment, which is difficult to achieve in method, or easy to disappear under large loads. Here, we report the outstanding robustness of frictional anisotropy caused by its own fold structure under high load. The frictional anisotropy is always larger than 200% between the armchair and zigzag direction of Se/Se interface under load up to 5.5 GPa and its maximum value reaches 325%. The frictional anisotropy between these two directions origins from the tremendous difference in charge density redistribution reflected only in direction perpendicular to interface, which is a novel method to quantitatively characterize friction from the perspective of electronic interaction. The load-induced weakening of friction anisotropy derives from the sudden change in chemical interactions between atoms around interface. The exploring of extreme frictional anisotropy caused by its own structure is not only helpful for a comprehensive understanding of frictional anisotropy behavior, but also contributes to the construction of nanodevices required the friction anisotropy to achieve, such as mechanical logic gates.

Experimental Decoding and Tuning Electronic Friction of Si Nanotip Sliding on Graphene.

Due to the coupled contributions of adhesion and carrier to friction typically found in previous research, decoupling the electron-based dissipation is a long-standing challenge in tribology. In this study, by designing and integrating a graphene/h-BN/graphene/h-BN stacking device into an atomic force microscopy, the carrier density dependent frictional behavior of a single-asperity sliding on graphene is unambiguously revealed by applying an external back-gate voltage, while maintaining the adhesion unaffected. Our experiments reveal that friction on the graphene increases monotonically with the increase of carrier density. By adjusting the back-gate voltage, the carrier density of the top graphene layer can be tuned from -3.9 × 1012 to 3.5 × 1012 cm-2, resulting in a ∼28% increase in friction. The mechanism is uncovered from the consistent dependence of the charge density redistribution and sliding barrier on the carrier density. These findings offer new perspectives on the fundamental understanding and regulation of friction at van der Waals interfaces.

Constructing Asymmetrical Coordination Microenvironment with Phosphorus‐Incorporated Nitrogen‐Doped Carbon to Boost Bifunctional Oxygen Electrocatalytic Activity

AbstractCarbon‐based metal‐free electrocatalysts have been recognized as inexpensive alternatives to afford excellent activity in oxygen reduction/evolution reactions (ORR/OER). Nevertheless, precisely identifying the local active sites and tailoring the corresponding electronic properties to enhance the reaction kinetics remain challenging. Herein, a facile strategy to create a metal‐free electrocatalyst comprised of a mesoporous nitrogen‐doped carbon matrix with phosphorus incorporation (NPC) is described. The as‐prepared NPC‐950 electrocatalyst demonstrates superior ORR activity under alkaline and acidic conditions with half‐wave potentials of 0.88 and 0.72 V, respectively, comparable to commercial Pt/C (0.85 and 0.76 V) and overwhelmingly superior to other N‐doped carbon catalyst materials. In addition, a remarkable promotion of OER activity under alkaline conditions is observed. Notably, a zinc–air battery equipped with this NCP‐950 electrocatalyst exhibits exceptional performance in peak power density, specific capacity, and long‐term operation durability. Theoretical calculations uncover that the incorporation of phosphorus in NC material results in effective charge density redistribution, thus modulating the electronic properties of active sites to achieve optimum adsorption and desorption of ORR intermediates. The work provides a deep understanding of active sites in heteroatom‐doped carbon materials and highlights the importance of the electronic properties modulation in oxygen bifunctional electrocatalytic activity.

Exploring the Relationship between the Structural Characteristics and Mechanical Behavior of Multicomponent Fe-Containing Phases: Experimental Studies and First-Principles Calculations.

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies and first-principles calculations. The results indicate that it is easier for Fe and Cr to substitute the Mn-12j site in α-AlMnSi in thermodynamics; Cr is preferred to Fe for substituting Mn-12j/k sites due to its lower formation enthalpy after single substitutions at Mn atom sites. The α-AlFeMnCrSi phase shows higher thermal stability, modulus and intrinsic hardness and a lower volumetric thermal expansion coefficient at different temperatures due to the strong chemical bonding of Si-Fe and Si-Cr. Moreover, the α-AlFeMnCrSi phase has a higher ideal strength (10.65 GPa) and lower stacking fault energy (1.10 × 103 mJ/m2). The stacking fault energy evolution of the different Fe-containing phases is mainly attributed to the differential charge-density redistribution. The strong chemical bonds of Si-Fe, Si-Mn and Si-Cr are important factors affecting the thermophysical and mechanical behaviors of the α-AlFeMnCrSi phase.

Improving Low-temperature Performance and Stability of Na2 Ti6 O13 Anodes by the Ti-O Spring Effect through Nb-doping.

Na2 Ti6 O13 (NTO) with high safety has been regarded as a promising anode candidate for sodium-ion batteries. In the present study, integrated modification of migration channels broadening, charge density re-distribution, and oxygen vacancies regulation are realized in case of Nb-doping and have obtained significantly enhanced cycling performance with 92 % reversible capacity retained after 3000 cycles at 3000 mA g-1 . Moreover, unexpected low-temperature performance with a high discharge capacity of 143 mAh g-1 at 100 mA g-1 under -15 °C is also achieved in the full cell. Theoretical investigation suggests that Nb preferentially replaces Ti3 sites, which effectively improves structural stability and lowers the diffusion energy barrier. What's more important, both the in situ X-ray diffraction (XRD) and in situ Raman furtherly confirm the robust spring effect of the Ti-O bond, making special charge compensation mechanism and respective regulation strategy to conquer the sluggish transport kinetics and low conductivity, which plays a key role in promoting electrochemical performance.

Mott Schottky heterojunction Co/CoSe2 electrocatalyst: Achieved rapid conversion of polysulfides and Li2S deposition dissolution via built-in electric field interface effect

Rechargeable lithium-sulfur (Li-S) batteries are considered ideal candidates for the next generation of energy storage devices. However, the insulation properties of S and Li2S, as well as the notorious “shuttle effect” of lithium polysulfide, result in severe loss of active sulfur, poor redox kinetics, and rapid capacity decline. To overcome these limitations, this paper designs a self-supporting electrocatalytic electrode based on Co/CoSe2 Mott Schottky heterojunction coated carbon nanofibers (Co/CoSe2@NCNFs), and engineers it for capturing and converting polysulfides. Density functional theory calculations show that the introduction of Co/CoSe2 heterojunction effectively reduces the redox barrier of Li2S. The electron current and electron interaction at the Co/CoSe2 interface induce the redistribution of charge density in the depletion region, thus increasing the chemical reactivity of the metal semiconductor heterojunction interface, which is conducive to the ion/electron transport, polysulfide conversion and Li2S oxidation process. Therefore, the Li-S battery assembled by Co/CoSe2@NCNFs/S electrode exhibited a high initial specific capacity of 1043.3 mAh/g at 1C, and maintained a capacity of 709.9 mAh/g after 1000 cycles, with a capacity decay rate of only 0.032% per cycle. The proposed Mott Schottky heterojunction as an electrocatalyst deepens the promotion of polysulfides and Li2S in long-life Li-S batteries.

Comparative Density Functional Theory Study of Magnetic Exchange Couplings in Dinuclear Transition-Metal Complexes.

Multicenter transition-metal complexes (MCTMs) with magnetically interacting ions have been proposed as components for information-processing devices and storage units. For any practical application of MCTMs as magnetic units, it is crucial to characterize their magnetic behavior, and in particular, the isotropic magnetic exchange coupling, J, between its magnetic centers. Due to the large size of typical MCTMs, density functional theory is the only practical electronic structure method for evaluating the J coupling. Here, we assess the accuracy of different density functional approximations for predicting the magnetic couplings of eight dinuclear transition-metal complexes, including five dimanganese, two dicopper, and one divanadium with known reliable experimental J couplings spanning from ferromagnetic to strong antiferromagnetic. The density functionals considered include global hybrid functionals which mix semilocal density functional approximations and exact exchange with a fixed admixing parameter, six local hybrid functionals where the admixing parameters are extended to be spatially dependent, the SCAN and r2SCAN meta-generalized gradient approximations (GGAs), and two widely used GGAs. We found that global hybrids tested in this work have a tendency to over-correct the error in magnetic coupling parameters from the Perdew-Burke-Ernzerhof (PBE) GGA as seen for manganese complexes. The performance of local hybrid density functionals shows no improvement in terms of bias and is scattered without a clear trend, suggesting that more efforts are needed for the extension from global to local hybrid density functionals for this particular property. The SCAN and r2SCAN meta-GGAs are found to perform as well as benchmark global hybrids on most tested complexes. We further analyze the charge density redistribution of meta-GGAs as well as global and local hybrid density functionals with respect to that of PBE, in connection to the self-interaction error or delocalization error.

Oxidation and corrosion investigation on Ti2AlV (110) surface using first principle approach

Ti-Al-V alloys are frequently used as structural materials in metallurgy, electronics, and other industrial sectors due to their exceptional qualities. However, the inherent limitations of the material include porosity, surface roughness, and a strong affinity for oxygen. The adsorption of oxygen and chlorine on metal surfaces is crucial, especially for catalysis and corrosion applications. In this study, the adsorption mechanism of oxygen and chlorine on the surface of Ti2AlV (110) is investigated using density functional theory. Surface oxidation and corrosion were compared using adsorption strength, work function, density of states, and charge density redistribution. The findings revealed that the adsorption behaviour of oxygen and chlorine is an exothermic and spontaneous reaction. Furthermore, the adsorption of oxygen has a negative adsorption energy higher than that of chlorine. Subsequently, various adsorption sites were examined on the surface, with the bridge sites being identified as the most stable adsorption configuration. In addition, a linear relationship was discovered between the adsorption energy strength and charge density redistribution. Electron depletion was observed on surface atoms, as well as charge accumulation on adsorbates. Moreover, adsorption was also discovered to alter the surface work function.

Macromolecules Promoting Robust Zinc Anode by Synergistic Coordination Effect and Charge Redistribution.

Zn dendrite formation is the main obstacle to commercializing aqueous zinc-ion batteries (ZIBs). α-cyclodextrin (α-CD) is proposed as an environmentally friendly macromolecule additive in the ZnSO4 -based electrolyte to obtain stable and reversible Zn anodes. The results show that α-CD molecules' unique 3D structure can effectively regulate the mass transfer of the electrolyte components and isolate the Zn anode from H2 O molecules. The α-CD provides abundant electrons to the Zn (002) crystallographic plane, which induces charge density redistribution. Such an effect relieves the reduction and aggregation of Zn2+ cations while protecting the Zn metal anode from water molecules. Finally, a small amount of α-CD additive (0.01 M) can enhance the performance of Zn significantly in Zn||Cu cells (1980 cycles with 99.45% average CE) and Zn||Zn cells (8000h ultra-long cycle life). The excellent practical applicability was further verified in Zn||MnO2 cells.

Modulating Water Splitting Kinetics via Charge Transfer and Interfacial Hydrogen Spillover Effect for Robust Hydrogen Evolution Catalysis in Alkaline Media.

Designing and synthesizing advanced electrocatalysts with superior intrinsic activity toward hydrogen evolution reaction (HER) in alkaline media is critical for the hydrogen economy. Herein, a novel Ir@Rhene heterojunction electrocatalyst is synthesized via epitaxially confining ultrasmall and low-coordinate Ir nanoclusters on the ultrathin Rh metallene accompanying the formation of Ir/IrO2 Janus nanoparticles. The as-prepared heterojunctions display outstanding alkaline HER activity, with an overpotential of only 17mV at 10mA cm-2 and an ultralow Tafel slope of 14.7mV dec-1 . Both structural characterizations and theoretical calculations demonstrate that the Ir@Rhene heterointerfaces induce charge density redistribution, resulting in the increment of the electron density around the O atoms in the IrO2 site and thus delivering much lower water dissociation energy. In addition, the dual-site synergetic effects between IrO2 and Ir/Rh interface trigger and improve the interfacial hydrogen spillover, thereby subtly avoiding the steric blocking of the active site and eventually accelerating the alkaline HER kinetics.

Metal-support interaction promoted multifunctional electrocatalysis on PtCo/NC with ultralow Pt loading for oxygen reduction reaction and zinc-air battery

Tri-functional PtCo/NC nanocatalysts were assembled via in-situ integration with ultralow Pt loading supported on ZIF-67 derived porous carbon material, and used as electrocatalysts for oxygen reduction reaction (ORR), ethanol oxidation reaction (EOR), hydrogen evolution reaction (HER). Detailedly, PtCo-3/NC with ultralow Pt loading (1 wt%) exhibits the halfwave potential of 0.877 V for ORR in acidic media and considerable current density for both ORR and EOR at 0.85 V, and low overpotential (η10 =10 mV) for HER. The as-assembled zinc-air batteries (ZABs) based on PtCo/NC have higher power density than Pt/C based ZABs. DFT calculation reveals the strong metal-support interactions (MSI) in PtCo/NC, which leads to the change of electronic state, redistribution of charge density and optimization of free energy, allowing it to present greater performances than Pt/C. This work highlights the possibility of using it as highly effective electrode catalysts with ultralow Pt loading in fuel cells and metal-air battery.

The Electric Field Evaluation for Vibrating Rain Droplets on the Overhead Line Conductors

The water droplets on the surface of the overhead line (OHL) conductors are subject to an intensive electric field, which induces electric force on the charged liquid surface. Under the combined action of the surface tension as well as the electric force, movement and deformation can be observed on those water droplets. These result in a re-distribution of charge density on the liquid surface and therefore a re-distribution of electric force. In this paper, in order to strengthen the understanding of this complex multi-physics problem of interaction and mutual coupling, the vibration characteristics of water droplets under alternating electric fields is studied using the finite element method (FEM). Parameters such as the volume size of the water droplet, static/dynamic contact angle between the water droplet and conductor surface and voltage level are studied in relation to the vibration characteristics. The reproducible correlation between the phase and amplitude of the water droplet vibration on the surface of the conductor and the applied voltage is established. According to the calculated instantaneous electric field strength, it is explained that protrusions such as water droplets are the starting point of corona discharge.

In-Plane Hydrogen Bonds and Out-of-Plane Dipolar Interactions in Self-Assembled Melem Networks

Melem (2,6,10-triamino-s-heptazine) is the building block of melon, a carbon nitride (CN) polymer that is proven to produce H2 from water under visible illumination. With the aim of bringing additional insight into the electronic structure of CN materials, we performed a spectroscopic characterization of gas-phase melem and of a melem-based self-assembled 2D H-bonded layer on Au(111) by means of ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In parallel, we performed density functional theory (DFT) simulations of the same systems to unravel the molecular charge density redistribution caused by the in-plane H-bonds. Comparing the experimental results with the spectroscopic DFT simulations, we can correlate the induced charge accumulation on the Namino atoms to the red-shift of the corresponding N 1s binding energy (BE) and of the Namino 1s → LUMO+n transitions. Moreover, when introducing a supporting Au(111) surface in the computational simulations, we observe a molecule–substrate interaction that almost exclusively involves the out-of-plane molecular orbitals, leaving those engaged in the in-plane H-bonded network rather unperturbed.

Insight into the effect of alloying on the adsorption of benzene on Ag(100) surface: DFT calculations

Heterogeneous catalysis, molecular sensors, and photovoltaics all rely on the interfaces between organic molecules and metal surfaces. Here, we study the adsorption of benzene on Ag(100) surface doped by Aun, Pdn, Ptn(n= 1–4), Au2Pd2, Au2Pt2 and Pd2Pt2 using density-functional theory (DFT), with the inclusion of van der Waals interactions, and compare with available computational and experimental result. The calculated quantities reveal that the interaction strength of Benzene with the surface gradually increases when it is doped by Pd or Pt atoms, showing a change in the nature of the interaction, from physisorption to chemisorption. We found that with surface allowing, one can tune the interaction strength. The charge transfer was found to occur from the molecule to the clean and doped surfaces with Au atoms and from the doped surface with Pd to the molecule. The redistribution of charge density indicates modifications in the features of the interface between the doped Ag(100) surfaces and benzene. In addition, alloying the Ag(100) surface with reactive TM changes substantially its electronic properties, which impacts its interactions with benzene. Finally, mixing two dopants or more can tune the electronic structure in designing more effective interfaces for various applications.