Electronic Charge Transfer Research Articles

Silver-induced γ→ε martensitic transformation in FeMn alloys: An experimental and computational study

Porous FeMn alloys with additions of 0, 1, 3 and 5 wt% of Ag were fabricated using powder metallurgy and sintering. The microstructure of the fabricated alloys was characterized using X-ray diffraction, transmission electron microscopy and selected area electron diffraction. While equiatomic FeMn and FeMn-1Ag alloys possess a fully austenitic structure, a change in the crystallographic structure is observed upon addition of 3 and 5 wt% of Ag, where a mixture of γ austenite and ε martensite phases is observed. Compression tests reveal that such structural transition causes an increase of the yield stress. The evolution of microstructure with the Ag content can be understood from theoretical calculations which show that Ag atoms prefer the intrinsic stacking fault (ISF) sites, revealing lower energy for the ε atomic plane sequence. This causes local depletion of the electronic charge, therefore weakening the interatomic bonds at the ISF plane and facilitating the phase transition. In addition, the total energy difference between the γ and ε phases decreases upon Ag addition. This enables the coexistence of both phases in the sample with 5 wt% Ag. Both experimental and theoretical data agree that the magnetization value gradually increases upon Ag addition. This is due to the local stress that is introduced by Ag atoms, which expand the Ag-Fe and Ag-Mn first neighbour interatomic bonds compared to FeMn. This stress results in electronic charge transfer that locally alters the Fe and Mn atomic magnetic moments. These results are appealing for the design of FeMn-based alloys with tuneable phase composition and physical properties for several technological applications.

Inelastic processes under gas cluster ion bombardment of metals

Total currents of positive and negative particles arising under bombardment of metal surfaces with argon gas cluster ions were measured for the energy range 2–15 keV. Supposing that the negative current was defined by secondary electrons, and the positive current is the flow of the reflected argon ions, the possible mechanisms of electron emission and charge transfer are discussed. The discussion is supported by molecular dynamics simulations of cluster-surface collisions.

Thermodynamic and electro-kinetic aspects of diffusion and migration (charge transfer) of electrons and holes across an n-p-type junction under bias and a photovoltaic cell under illumination

Thermodynamic and electro-kinetic aspects of diffusion and migration (charge transfer) of electrons and holes across an n-p-type junction under bias and a photovoltaic cell under illumination

A first principles study on the catalytic performance of methylcyclohexane dehydrogenation on a monoatomic catalyst

SummaryThis research explores how methylcyclohexane (MCH) interacts with individual metal atoms M (M= Pt, Pd, and Cu) based on density functional theory (DFT) total energy calculations. We analyzed the adsorption energies of MCH on these metal atoms to understand their stability and reactivity. The results show that MCH prefers to attach to single Pt atoms, which exhibited the strongest adsorption energy. Compared with Pt(111) surfaces, the adsorption energies on Pt atoms were slightly higher, indicating enhanced stability at the nanoscale. Adsorption on Pd and Cu atoms resulted in lower adsorption energies than on Pt. We also focused on the initial step of dehydrogenation, where we studied the removal of one hydrogen atom (H1) from MCH. The presence of a single metal atom significantly lowered the energy required for breaking the C1–H1 bond, with Pt showing the lowest energy barrier compared with Pd and Cu due to the excessive of charge transfer. We analyzed the electronic properties and charge transfer during dehydrogenation, revealing the influence of the metal atom's electronic structure on catalytic behavior. Overall, this research provides valuable insights into how MCH interacts with monoatomic metal catalysts, emphasizing the role of the metal atom's electronic configuration in determining reactivity.

Performance of BiCu2O modified Pd/C as an anode electrocatalyst for direct ethanol fuel cell system

BiCu2O Modified Pd/C nanocatalyst was synthesised via an eco-friendly method for fuel cell application. The obtained nanomaterials' structural composition, and electrochemical properties were investigated using chemical and physical techniques such as impedance spectroscopy (EIS), X-ray diffraction (XRD), high resolution-scanning electron microscopy (HR-SEM), and cyclic voltammetry (CV). The preparation of the BiCu2O Modified Pd/C catalyst was successfully verified by microscopic techniques, as shown by the presence of mixed nanostructures, Pd and BiCu2O coexisting. EIS measurements confirmed a smaller electron charge-transfer (160 Ω) for the prepared Pd/C-BiCu2O nanocatalyst. From the Pd oxide peaks, the electrochemical active surface area (EASA) values for Pd/C-BiCu2O and Pd/C were estimated to be 432.1 cm2 mg−1 and 79.2 cm2 mg−1, respectively. The resulting BiCu2O Modified Pd/C nanocatalyst showed increased ethanol oxidation activity (If/Ib=1.1) and was more resistant to poisoning by advanced oxidation species. Under passive conditions at 1 M ethanol in 1 M KOH, improved cell performance (cell output = 120 mW) with a high density of current (105 mAcm−2) and power density (25.7 mWcm−2) relative to the commercial Pd/C were obtained. The study opens and forges novel possibilities in the search for new carbon co-catalysts for direct ethanol fuel cell (DEFC) application because of the simplified green processing and the cost of the precursor and the Pd-based catalyst produced. The work involves using difficult waste streams produced by various agro-industrial operations to create high surface material for use in producing commodities with added value. This work will also help address climate action, clean and affordable energy crisis.

Electronic and optical properties of Be2C/graphene heterojunction from first-principles calculations

We study the electrical and optical properties of the van der Waals (vdW) heterojunction Be2C/graphene by first principles. The constructed heterojunction exhibits p-type Ohmic contact. It is found that the varied interlayer distance and biaxial stress can influence the electronic structure and charge transfer of heterojunction. While the small variety of the difference of electrostatic potential of the heterojunction induces the small change of charge transfer at the contact interface, so the p-type Ohmic contact can still be formed. Meanwhile, the decreased interlayer distance and tensile strain can enhance the optical absorption of heterojunction. Then we calculate the external quantum efficiency of the optoelectronic device based on Be2C/graphene that reaches to 27.8%. This work provides a way to design electronic and optoelectronic devices based on Be2C/graphene in the future.

Conducting polymer encrusted Cu/Mn-MOF-CNDs: A facile synthesis, characterization and its hydrogen evolution activity in alkaline media and seawater

The Composites of polyaniline-bimetallic metal-organic framework with carbon nanodots (PANI/bi-MOF@CNDs) were fabricated by chemically oxidising aniline monomer for the hydrogen evolution process (HER). In this investigation, the composite structure, topography, and characteristics were analysed. The Fourier transform infrared spectroscopy analyses found evidence of electrostatic interaction between the CNDs@MOF and the backbone of the PANI matrix. Investigations using scanning electron microscopy and transmission electron microscopy showed that the CNDs@MOF exhibited uneven crystals with an additional enveloping PANI material. In an alkaline medium, the produced PANI composite (PANI/bi-MOF@CNDs) electrocatalyst showed a small overpotential and significant Tafel slope (110 mV and 180 mV/dec at 10 mA/cm2), as well as the RCT value of about 12.26 Ω, determined from Nyquist plot. PANI composite structural characteristics and electrical conductivity have also resulted in a faster rate of electron charge transfer and more accessible surface edge active sites. In addition, the catalyst is stable for 48 h at the specified operating conditions, and no further buffered electrolytes are required. As a result of the enhanced electrochemical performance, a strategic approach for the development of low-priced electrocatalysts for power conversion has been discovered.

Effects of Bi-doping on structure and properties of YBaCo2O5+δ layered perovskite cathode for intermediate-temperature solid oxide fuel cells

Layered perovskite oxides, Y1–xBixBaCo2O5+δ (YBBCx, x = 0.0–0.2) were investigated as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results indicate the YBBCx could be indexed to a tetragonal phase with trace of 3 × 3 × 1 superstructure configuration. No significant change in thermal expansion coefficients (TECs) was detected with the Bi-doping, and the TECs were 15.7–16.8 × 10−6 K−1 at 100–935 °C in air. Although the Bi-doping results in a decrease in conductivity of the YBBCx, the x = 0.2 sample still shows higher conductivity than that of a standard SOFC cathode (∼100 S cm−1). Additionally, the Bi-doping leads to an enhancement in the electrochemical performance mainly due to improved ion and electron charge transfers. Among the YBBCx compositions, the YBBC0.2 cathode shows the lowest polarization resistance (Rp) of 0.034 Ω cm2 at 700 °C. For a single cell with 300 µm thick La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM) and YBBC0.2 cathode, a peak power density (Pmax) of 537 mW cm−2 at 700 °C was achieved with no significant deterioration in performance after a 100–h testing.

Reversible Electrochemical Anionic Redox in Rechargeable Multivalent-Ion Batteries.

Rechargeable multivalent-ion batteries are of significant interest due to the high specific capacities and earth abundance of their metal anodes, though few cathode materials permit multivalent ions to electrochemically intercalate within them. The crystalline chevrel phases are among the few cathode materials known to reversibly intercalate multivalent cations. However, to date, no multivalent-ion intercalation electrodes can match their reversibility and stability, in part due to the lack of design rules that guide how ion intercalation and electron charge transfer are coupled up from the atomic scale. Here, we elucidate the electronic charge storage mechanism that occurs in chevrel phase (Mo6Se8, Mo6S8) electrodes upon the electrochemical intercalation of multivalent cations (Al3+, Zn2+), using solid-state nuclear magnetic resonance spectroscopy, synchrotron X-ray absorption near edge structure measurements, operando synchrotron diffraction, and density functional theory calculations. Upon cation intercalation, electrons are transferred selectively to the anionic chalcogen framework, while the transition metal octahedra are redox inactive. This reversible electrochemical anionic redox, which occurs without breaking or forming chemical bonds, is a fundamentally different charge storage mechanism than that occurring in most transition metal-containing intercalation electrodes using anionic redox to enhance energy density. The results suggest material design principles aimed at realizing new intercalation electrodes that enable the facile electrochemical intercalation of multivalent cations.

Hexagonal Boron Nitride/Reduced Graphene Oxide Heterostructures as Promising Metal‐Free Electrocatalysts for Oxygen Evolution Reaction Driven by Boron Radicals

Developing highly efficient earth‐abundant alternatives to traditional noble metal catalysts is essential for clean and sustainable energy‐conversion and energy‐storage technologies, yet still challenging in limited active sites and weak resistance to electrochemical corrosion. Herein, density‐functional theory calculations demonstrate that hexagonal boron nitride (h‐BN), albeit often being considered inert, can generate boron‐active radicals at defective sites by forming heterogeneous structures with graphene‐containing point vacancies, leading to a substantial electron delocalization and charge transfer, indicating a superior catalytic activity. Experimentally, the van der Waals heterostructure is rationally designed with h‐BN nanosheets (BNNs) anchored on reduced graphene oxide (rGO) as strongly coupled composite catalysts. Despite the poor conductivity in BN and lower catalytic activity in rGO, the created heterostructures demonstrate unexpected, improved oxygen evolution reaction (OER) activity with excellent stability in alkaline electrolyte. Qualitative analysis of the valence band offset and theoretical calculation reveal that the formation of heterostructures can significantly drive the electron transfer between C and B atoms near the vacancies across the interface and cause a half‐metallic property of BN, decreasing the free energy barrier of four‐electron OER kinetics. Herein, the synthetic schemes of h‐BNNs are guided as highly active metal‐free OER electrocatalysts.

2D stacking of graphene and boron nitride for efficient metal free overall water splitting

Constructing bifunctional electrocatalysts is essential for efficient water splitting. Rational interface engineering is an effective method for modifying active sites and promoting electronic charge transfer, resulting in improved water splitting efficiency. In this study, we designed a metal-free, 2D structure of graphene and boron nitride (h-BN). 2D stacking of two different layers generated abundant interfaces as well as huge electrochemical active sites. As a result, the graphene/h-BN stacked structure has a very low overpotential of 28 mV (for 10 mA/cm2 current density) for hydrogen evolution. At the same time, a significantly low overpotential of 360 mV (for 50 mA/cm2 current density) was achieved for oxygen evolution. The stacked structure of graphene/h-BN has been effectively utilized as a promising cathode and anode in a two-electrode system for accomplishing overall water splitting. Thus, our investigation suggests that rational construction of heterogeneous interfaces by stacking different 2D nanostructures can accelerate the overall water splitting by maximizing the electrochemical performance.

Pseudotetrahedral C2-symmetrical Co/Zn(II)-achiral Schiff base complexes with Δ/Λ-chirality induction at-metal as a racemic mixture

Reaction of achiral Schiff base ligands 1-((X-phenylimino)methyl)naphthalen-2-ol {X = 2-ethyl (HL1) or 4-methyl (HL2)} with cobalt(II) or zinc(II) acetate provided the corresponding bis[1-((X-phenylimino)methyl)naphthalen-2-olato-k2N,O]cobalt(II) or zinc(II) {X = 2-ethyl: M = Co (1) and Zn (2) or X = 4-methyl: M = Co (3) and Zn (4)} complexes. The molecules crystallize in the centrosymmetric space groups R–3 (1) and P–1 (3 or 4). Molecular structures determinations showed coordination of two molecules of the N,O-chelate ligands to the metal ion and formation of pseudotetrahedral complexes with C2-symmetry. Furthermore, coordination of two unsymmetrical achiral N,O-chelates induces Λ/Δ-chirality at the metal atom as a racemic mixture in the centrosymmetric space groups. Structural analyses further reveal that incorporation of 2-ethyl (1) or 4-methyl (3 or 4) group on the N-bound phenyl ring leads to an increase of both the O1-M-O2 and N1-M-N2 bond angles on going from 1 to 3 or 4, with the N1-M-N2 angle increasing to a much greater extent. The fair matching of the experimental and simulated powder X-ray diffraction patterns confirms the phase purity of bulk microcrystalline sample. Differential scanning calorimetry (DSC) results suggest an irreversible phase transformation from solid crystals to isotropic-liquids and subsequent thermal stability of the complexes. Cyclic voltammograms indicate a quasi-reversible two one electron charge transfer processes for 1 or 3 in N,N-dimethylformamide (DMF). Optimized geometry and excited state properties by density functional theory (DFT) and time dependent-density functional theory (TD-DFT) calculations correspond well to the experimental results.

A Comparative Study on Gemological Characteristics and Color Formation Mechanism of Moqi Agate, Inner Mongolia Province, China

Agate attracts the attention of gem mineralogists because of its variable colors. The color of agate is closely related to its naming and classification, so it is necessary to study the color and mineral origin of agate. In this paper, the mineralogical characteristics and color origin of red, yellow and green Moqi agates from Inner Mongolia were systematically studied by means of Fourier transform infrared spectrometer, Raman spectrometer, X-ray powder diffractometer, electron probe microanalyzer and ultraviolet–visible spectrophotometer. It is found that the color of Moqi agate is related to the minerals and trace elements contained in it, and is associated with the electron transition or charge transfer of Fe ions in the contained minerals. Green agate has the highest Fe content, and its color is caused by celadonite inclusions. The red and yellow color in Moqi agate is mainly caused by hematite and goethite, while red agate contains more Fe than yellow agate. Raman spectroscopy and X-ray diffraction analysis show that the content of moganite in Moqi agate is 0–30%. It is calculated that the crystallinity of Moqi agate is 1.5–3.5. This work provides a theoretical basis for future research on the identification of Moqi agate.

A computational approach for screening carbazole based organic dyes as potential photosensitizers for DSSCs application

The scientific community has shown significant interest in organic materials due to their potential applications in optoelectronics. In this study, we present the design and theoretical investigation of a new class of carbazole-based organic chromogens (R1-6). These chromogens consist of a heteroaromatic carbazole unit as an electron-rich donor, connected to a substituted phenyl ring carrying various electron acceptor groups. Specifically, we analyse the structural impact of electron withdrawing moieties such as carboxylic acid (–COOH), cyano (–CN), and nitro (–NO2) on the photophysical properties of these chromogens. To gain insights into the electron density localization and charge transfer characteristics, we perform DFT, TD-DFT, and MESP calculations. The computational studies indicate that these materials exhibit promising potential as sensitizers for applications in dye-sensitized solar cells (DSSCs).

Preparation of dual-use GPTES@ZnO photocatalyst from waste warm filter cake and evaluation of its synergic photocatalytic degradation for air-water purification

Organic pollutants are the most critical threats to the health of air and water resources. On this basis, fabricating a photocatalytic acrylic film with dual-use (i.e. removing benzene from air and MB/MO dyes from water) was aimed in this research. For this purpose, waste warm filter cake (WWFC) was used to extract zinc from it. Zinc element was separated from WWFC by a basic leaching method and acidified to prepare zinc oxide nanoparticles. In the following, a simple hydrothermal method was used to increase the surface functionality of the extracted ZnO nanoparticles in order to establish active reaction sites for reaction to silane coupling agent and increase in the holes that were prepared during photo-excitation. Thereafter, the nanoparticles were modified with 3-glycidoxypropyltriethoxysilane (GPTES) at different concentrations. The band gap of the modified nanoparticles decreased from 3.25 to 3.1 eV by surface modification. The photocatalytic performance of ZnO nanoparticles was assessed by degradation of MB and MO aqueous solution (50 ppm) under simulated UV/Visible irradiations. MB and MO were degraded 91 and 60% under UV light and 65 and 50% under visible light after 150 min of irradiation. The photo degradation rate increased after adding carboxy methyl cellulose (CMC) surfactant to methylene blue and adding cocamide-dea (CDE-G) surfactant to methyl orange. The results confirmed that the green surfactants improve the dispersion and surface interaction of the modified nanoparticles in the dyes solution and cause more electron charge transfer which creates effective photocatalytic sites. The prepared nanocomposite films were placed in a photo-reactor to remove gaseous benzene from air under UV/visible irradiation. Gas chromatography (GC) results showed that the modified nanoparticles removed up to 35.25 and 20.34% of benzene from air. Colorimetric analysis (ΔE*) showed that the acrylic film contained modified nanoparticles degraded 91 and 82% of MB, and 85 and 76% of MO under UV/visible lights, respectively. In the end, it can be said that these photocatalytic films are able to remove environmental pollution in air and water.

The effect of biaxial strain on the electronic structures and optical properties of GaS/SSnSe heterojunction: A first-principles calculations

Due to their tunable electronic structures and superior optical properties, vertically stacked heterojunctions have received considerable attention. In this paper, the electronic structure, charge transfer, and optical properties of the GaS/SSnSe heterojunction are investigated by first-principles calculations. According to our findings, the GaS/SSnSe heterojunction is a semiconductor with an indirect band gap and a Type-I band alignment. The band alignment of the heterojunction can be linearly tuned by the biaxial strain, which induces a semiconductor-to-metal transition. Moreover, the absorption coefficient of the heterojunction becomes higher and the absorption spectrum appears blue-shifted compared to each monolayer material. The above findings provide a theoretical support for the application of the heterojunction in ultraviolet light detection and tunable devices fields.

Single-electron charge transfer into putative Majorana and trivial modes in individual vortices

Majorana bound states are putative collective excitations in solids that exhibit the self-conjugate property of Majorana fermions—they are their own antiparticles. In iron-based superconductors, zero-energy states in vortices have been reported as potential Majorana bound states, but the evidence remains controversial. Here, we use scanning tunneling noise spectroscopy to study the tunneling process into vortex bound states in the conventional superconductor NbSe2, and in the putative Majorana platform FeTe0.55Se0.45. We find that tunneling into vortex bound states in both cases exhibits charge transfer of a single electron charge. Our data for the zero-energy bound states in FeTe0.55Se0.45 exclude the possibility of Yu–Shiba–Rusinov states and are consistent with both Majorana bound states and trivial vortex bound states. Our results open an avenue for investigating the exotic states in vortex cores and for future Majorana devices, although further theoretical investigations involving charge dynamics and superconducting tips are necessary.

Basicity and Nucleophilicity Effect in Charge Transfer of AlH3-Base Adducts: Theoretical Approach

This study permits to explore the interactions involved in Lewis acid (AlH3) and Lewis bases: CO; H2O; NH3; PH3; PC13; H2S; CN–; OH–; O2–2; F–; N(CH3)3; N2; N2H4; N2H2; C5H5N; C6H5-NH2. By means of DFT theory calculations with B3LYP functional using 6-31G(d,p) basis set and in order to check the effects of both the donor and the acceptor in the establishment of the different adducts we focused mainly on the calculation of the energetic gap ∆EHOMO-LUMO, Gibbs energies ∆G, the angle (θ) in AlH3-base and the interaction energy values Einter. The several parameters of the reactivity (electrophilicity index (ω), nucleophilicity (N), chemical potential (μ), hardness (η), and polarizability (α)) are also calculated to define the weak interaction as well as to distinguish between the nucleophilicity and basicity of different Lewis bases. The results showed that the electronic charge transfer is estimated to be important in the systems where the interaction is established between Al and anionic bases, and the electron donor power is predictable for O–2, F–, OH–, and CN–. The pseudo-tetrahedral adduct arrangements depend on the parameter geometries (bond length interaction and θ angle) and Gibbs energies ∆G characterizing the main stability.

Carcinogenic dioxane detection using pristine and metal-doped 2D VSe2: Insights from density functional theory simulations

Dioxane (diethylene oxide) is a synthetic organic compound classified as heterocyclic ether, a potentially carcinogenic water toxicant. Prolonged exposure can cause eye irritation, carcinogenic liver reactions, and other severe issues. Therefore, efficient dioxane detectors are needed to be designed and developed. Inspired by the recent developments of 2D materials in biosensing, in this work, the dioxane detection potentiality of pristine and metal-doped (Al, Au, and Ag) 2D VSe2 have been systematically examined using Density Functional Theory (DFT) based simulations. Among all the metallic dopants considered, Al binds energetically on the VSe2 surface with an energy of −2.158 eV. The adsorption of dioxane was studied by considering the electronic properties, adsorption energy, orbital interactions, and charge transfer. Our DFT calculation suggests that dioxane adsorption in Al-doped VSe2 is more promising than the pristine and other metal-doped VSe2 systems, due to the reasonable adsorption energy of −0.80 eV, charge transfer of −0.567e, and strong orbital interaction between Al 3p and O 2p orbitals. Additionally, the room temperature structural solidity of the sensor has also been verified using the ab initio molecular dynamics simulations. The reported theoretical results inspire the fabrication and engineering of efficient dioxane sensors using Al-doped VSe2.

Electrochemical performance of gold-decorated graphene electrodes integrated with SiC

Here we investigate the interface properties of gold (Au) decorated graphenized surfaces of 4H-SiC intended for electrochemical electrodes. These are fabricated using a two-step process: discontinuous Au layers with a nominal thickness of 2 nm are sputter-deposited onto 4H-SiC substrates with different graphenization extent—zero-layer graphene (ZLG) and monolayer epitaxial graphene) —followed by thermal annealing. By performing combined morphometric analysis, Raman mapping analysis, conductive atomic force microscopy, and electrochemical impedance spectroscopy measurements, we shed light on the relationship between physical processes (Au intercalation, particle re-shaping, and de-wetting) caused by thermal annealing and the intrinsic properties of graphenized SiC (vertical electron transport, charge-transfer properties, vibrational properties, and catalytic activity). We find that the impedance spectra of all considered structures exhibit two semicircles in the high and low frequency regions, which may be attributed to the graphene/ZLG/SiC (or Au/graphene/ZLG/SiC) and SiC/ZLG/graphene/electrolyte (or SiC/ZLG//Au/electrolyte) interfaces, respectively. An equivalent circuit model is proposed to estimate the interface carrier transfer parameters. This work provides an in-depth comprehension of the way by which the Au/2D carbon/SiC interaction strength influences the interface properties of heterostructures, which can be helpful for developing high performance catalytic and sensing devices.