Electron Interaction Effects Research Articles

Metal-organic frameworks derived FeS2@CoS2 heterostructure for efficient and stable bifunctional electrocatalytic water splitting

The exploration of efficient metal-based bifunctional catalysts for electrochemical water splitting is a promising approach for large-scale applications. In this work, we constructed a FeS2@CoS2 heterostructure electrocatalyst by a facile solution-dipping and hydrothermal method. The optimum FeS2@CoS2 heterostructure showed notable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances, with overpotential values of 280 mV and 136 mV (10 mA cm−2 current density), respectively. Additionally, the electrocatalyst exhibited a robust stability performance of 50 h at a current density of 10 mA cm−2. The two-cell electrolyzer is assembled using FeS2@CoS2||FeS2@CoS2 and delivers a cell voltage of 1.62 V and 1.99 V at 10 and 50 mA cm−2 current densities with excellent durability. The outstanding overall water-splitting activity of the obtained heterostructure can be attributed to effective electronic interactions, synergistic effects, and exposure of more reactive active sites in the electrocatalyst. This work presents a promising strategy for developing highly active and cost-effective metal sulfide-based bifunctional electrocatalysts for energy conversion technology.

Anchoring Ru nanoparticles on Ti3C2Tx for accelerated alkaline hydrogen evolution reaction: The effect of electronic metal-support interaction

Electrocatalytic hydrogen evolution reaction (HER) in the alkaline media is a promising strategy for energy conversion. Nevertheless, the sluggish kinetics of alkaline HER hinders its commercial application. Electronic metal-support interaction (EMSI) is an efficient approach to regulate the electronic state of active sites and enhance the electrocatalytic HER performance. Hence, we demonstrate an efficient alkaline HER catalyst comprising Ruthenium nanoparticles (Ru NPs) homogeneously anchored on Ti3C2Tx (Ru-Ti3C2Tx), resulting in the formation of EMSI effect between Ru and Ti3C2Tx. Spectroscopy characterizations and theoretical calculations demonstrate that EMSI facilitated the charge transfer from Ru NPs to Ti3C2Tx. The regulation of local electron density on Ru NPs directly influenced hydrogen adsorption Gibbs free energy (ΔGH*), which optimized the adsorption of hydrogen intermediates (H*) on Ru NPs and promoted the formation of H2 molecules. Therefore, the obtained 5 % Ru-Ti3C2Tx catalyst displayed an outstanding HER performance with the overpotential of 46 mV and 60 mV at 10 and 200 mA·cm−2 in 1.0 M KOH, respectively. Furthermore, the cathode presented excellent stability during 20 h long-term measurements. This study presents some recommendations and guidance for constructing Ru-based catalysts to accelerate HER kinetics in alkaline media.

TiO2 nanotubes modified with cobalt oxyphosphide spheres for efficient electrocatalytic hydrogen evolution reaction in alkaline medium

Electronic and surface modulation through coupling between oxygen and phosphorous in cobalt oxyphosphide (CoOP) is identified as an effective approach to enhancing the electrocatalytic hydrogen evolution reaction (HER) in an alkaline medium. This work demonstrates a one-step and safe electrodeposition method to modify the surface of ordered titania nanotubes (TNTs) with CoOP spheres. The effect of electrodeposition charge density, pH of the electrodeposition bath, and presence of citric acid on the electrocatalytic HER performance of CoOP-modified TNTs was investigated. The Ti/TNTs/CoOP electrode requires only 130 mV overpotential to deliver 10 mA cm−2 in a 1.0 M KOH electrolyte. The Tafel slope is estimated to be 72.5 mV dec−1. Both the HER performance and Tafel value of Ti/TNTs/CoOP are superior to CoOP deposited on bare Ti foil (165 mV and 78.4 mV dec−1), FTO (185 mV; 88.1 mV dec−1), and glassy carbon (214 mV; 93 mV dec−1). The electrochemically active surface area (ECSA) and impedance spectroscopy findings revealed that the synergistic coupling between the CoOP and TNTs enhances the surface area and density of accessible active sites while reducing the charge transfer resistance at the electrode/electrolyte interface. Such a synergistic effect is ascribed to the effective electronic interaction between CoOP and TNTs, and the faster electron transfer kinetics because of the unidirectionality of the 1-D TNTs.

Catalytic boosting on AuCu bimetallic nanoparticles by oxygen-induced atomic restructuring

Understanding the structure-activity relationship over silica-supported Au-based bimetallic nanocatalysts in CO oxidation is essential in elucidating active sites and catalytic mechanisms. Here, we uncover that structure-activity relationship over a silica-supported 10 nm sized AuCu bimetallic model nanocatalyst for CO oxidation. Oxygen–induced atomic restructuring of AuCu nanocrystals is comprehensively investigated using combined operando spectroscopic and microscopic techniques, including near-ambient-pressure X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier-transform spectroscopy, and environmental transmission electron microscopy. We show that the formation of CuOx/Au heterostructure gives rise to the enhancement of catalytic activity for CO oxidation. The formation of the reactive heterostructure on catalysis was rationalized by density functional theory calculation. Our results indicate that intermediate heterostructure with a metal-oxide interface leads to strong electronic coupling between catalyst and support (i.e., electronic metal-support interaction effect).

Molecule‐Electrode Interfaces Controlled by Bulky Long‐Legged Ligands in Organometallic Molecular Wires

AbstractPrecise control of molecule‐electrode interface is essential for molecular devices. Herein, new ruthenium acetylide molecular wires with long‐legged phosphine ligands to form a sterically controlled molecule‐electrode interface are designed. The sharpened Raman signals ascribed to acetylene stretching are observed for the self‐assembled monolayers (SAMs) of the molecular wires with the biphenyl‐ (2Au) and tert‐butylbiphenyl‐substituted long‐legged dppe‐type ligands (3Au), suggesting that steric hindrance causes formation of uniform SAMs. Scanning tunneling microscope break‐junction (STM‐BJ) study of 3Au reveals narrow conductance features compared with those of 1Au bearing the parent dppe ligands, indicating formation of a uniform molecular junction. Furthermore, the effective electronic interactions between the molecule and electrodes are unique to the long‐legged derivatives, as revealed by the surface‐enhanced Raman scattering study. Thus, the bulky long‐legged strategy turns out to provide a design concept for a well‐defined molecule‐electrode interface.

C≡N vacancy engineering of Prussian blue analogs for the advanced oxygen evolution reaction

Hydrogen production by electrocatalytic water splitting suffers from the sluggish kinetics of the oxygen evolution reaction (OER) and large power consumption and hence, efficient OER electrocatalysts are required to enhance the energy conversion efficiency. Vacancies can create active unsaturated coordination, regulate the electronic structure, and enhance the charge transfer efficiency to improve both the intrinsic and extrinsic catalytic activities. This work aims to construct an efficient OER electrocatalyst through precise control of the C≡N vacancies (VC≡N) in NiFe- and NiCo-Prussian blue analogs (PBAs) leading to outstanding OER characteristics and improved energy conversion efficiency. The amount of VC≡N has been regulated precisely via thermal treatment. The electronic interactions occur between Ni and Fe sites during the introduction of VC≡N. As a result, the synergistic effects of Ni-Fe electronic interactions and VC≡N lead to outstanding OER characteristics such as a small overpotential of 270 mV to achieve a high current density of 50 mA cm−2 as well as excellent stability over 80 h, which are better than those of the pristine PBAs electrocatalyst. The results demonstrate a precise strategy to produce VC≡N in PBAs-based electrocatalysts for advanced OER and efficient hydrogen production.

Modelling kilonova afterglows: Effects of the thermal electron population and interaction with GRB outflows

AbstractGiven an increasing number of gamma-ray bursts accompanied by potential kilonovae, there is a growing importance to advance modelling of kilonova afterglows. In this work, we investigate how the presence of two electron populations that follow a Maxwellian (thermal) and a power-law (non-thermal) distribution affect kilonova afterglow light curves. We employ semi-analytic afterglow model, PyBlastAfterglow. We consider kilonova ejecta profiles from ab-initio numerical relativity binary neutron star merger simulations, targeted to GW170817. We do not perform model selection. We find that the emission from thermal electrons dominates at early times. If the interstellar medium density is high (${\simeq }0.1\, \, \text{cm}^{-3}$), it adds an early time peak to the light curve. As ejecta decelerates, the spectral and temporal indexes change in a characteristic way that, if observed, can be used to reconstruct the ejecta velocity distribution. For the low interstellar medium density, inferred for GRB 170817A, the emission from the non-thermal electron population generally dominates. We also assess how kilonova afterglow light curves change if the interstellar medium has been partially removed and pre-accelerated by laterally expanding gamma-ray burst ejecta. For the latter, we consider properties informed by observations of GRB170817A. We find that the main effect is the emission suppression at early time ${\lesssim }10^{3}\,$ days, and at its maximum it reaches ${\sim }40{{\ \rm per\ cent}}$ when the fast tail of the kilonova ejecta moves subsonically through the wake of laterally spreading gamma-ray burst ejecta. The subsequent rebrightening, when these ejecta break through and shocks form, is very mild (${\lesssim }10{{\ \rm per\ cent}}$) and may not be observable.

In the quest for an optimal parametric regime of nonadiabatic switching ensuring low heat release in conjunction with high polarizability of mixed-valence molecular dimers.

The effects of electronic and vibronic interactions on the specific heat release occurring in the course of nonadiabatic switching of the electric field polarizing a one-electron mixed-valence dimer is analyzed within the framework of the Piepho-Krausz-Schatz vibronic model. The search for an optimal parametric regime from the point of view of minimizing heat release is carried out taking into account the requirement to maintain a strong nonlinear response of the dimer to the applied electric field. Calculations of the specific heat release and the response performed in the framework of the quantum mechanical vibronic approach show that although the heat release is minimal under a weak electric field acting on the dimer in combination with weak vibronic coupling and/or strong electron transfer, such a combination of the parameters is incompatible with the requirement of a strong nonlinear response. Unlike this, for molecules exhibiting strong vibronic interactions and/or weak transfer, a rather strong nonlinear response can be obtained even with a very weak electric field, which, in turn, ensures low heat release. Thus, we can conclude that an efficient strategy to improve characteristics of molecular quantum cellular automata devices or other molecular switchable devices based on mixed-valence dimers consists in usage of molecules subjected to the action of a weak polarizing field, which are characterized by strong vibronic coupling and/or weak transfer.

Spectroscopic and Electrochemical Investigation of Peripherally Diruthenated Complexes of octakis(benzylthio) and (methylthio)tetraazaporphyrinmagnesium(II)

Four new trinuclear complexes were successfully synthesized through the dative binding of one unit of (bpy)2RuII and one unit of (phen)2RuII to the periphery of octakis(benzylthio)tetraazaporphyrinmagnesium(II) [Mg(OBTTAP)] and octakis(methylthio)tetraazaporphyrin- magnesium(II) ([Mg(OMTTAP)]). Spectroscopic techniques were used to perform an extensive characterization of the complexes, including an analysis of their fluorescence excitation/emission spectra and redox behaviours. Effective electronic interaction between the peripheral (bpy)2RuII/(phen)2RuII and [Mg(OBTTAP)] units is evidenced by the presence of these complexes. In cyclic voltammetry, the oxidation waves were slightly altered to a higher positive potential upon attaching a second Ru(II) unit in complexes 6, 7, 8 and 9.

Effective Low-Energy Hamiltonians and Unconventional Landau-Level Spectrum of Monolayer C3N.

We derive low-energy effective k·p Hamiltonians for monolayer C3N at the Γ and M points of the Brillouin zone, where the band edge in the conduction and valence band can be found. Our analysis of the electronic band symmetries helps to better understand several results of recent ab initio calculations for the optical properties of this material. We also calculate the Landau-level spectrum. We find that the Landau-level spectrum in the degenerate conduction bands at the Γ point acquires properties that are reminiscent of the corresponding results in bilayer graphene, but there are important differences as well. Moreover, because of the heavy effective mass, n-doped samples may host interesting electron-electron interaction effects.

Breakdown of topological protection due to nonmagnetic edge disorder in two-dimensional materials in the quantum spin Hall phase

We study the suppression of the conductance quantization in quantum spin Hall systems by a combined effect of electronic interactions and edge disorder, that is ubiquitous in exfoliated and chemical vapor deposition grown two-dimensional (2D) materials. We show that the interplay between the electronic localized states due to edge defects and electron-electron interactions gives rise to local magnetic moments, that break time-reversal symmetry and the topological protection of the edge states in 2D topological systems. Our results suggest that edge disorder leads to small deviations of a perfect quantized conductance in short samples and to a strong conductance suppression in long ones. Our analysis is based on the Kane-Mele model, an unrestricted Hubbard mean-field Hamiltonian, and on a self-consistent recursive Green's function technique to calculate the transport quantities.

Enhanced removal of tetracycline over CeMO-7 % nanorods via electronic interaction effect: Degradation, kinetics and mechanism

Although multifarious strategies, including oxygen vacancies or surface defects improvement, morphology modification, crystal phase transition and ion doping, have been developed for improving the catalytic performance of MnO2 in the removal of pollutant substances. As far as we know, there is the first report providing enhanced performance of MnO2 in the removal of pollutant substances by its electronic interaction effect. Herein, this study proposes a facile and high-efficiency method to achieve Ce-doping manganese oxide (CeMO) nanorods for the enhanced tetracycline removal via electronic interaction effect at 30 °C for the first time. The detailed characterizations and anions effect experiment have confirmed that CeMO-7 % nanorods possessed abundant surface reactive oxygen species, which is in favor of PMS activation. Compared to manganese oxide (MO), CeMO-5 % and CeMO-9 %, an obvious left shift has been observed in the Mn 2p of CeMO-7 %, suggesting that some electrons are transferred from Mn atoms to Ce atoms in CeMO-7 %, and implying that the highest degradation efficiency of CeMO-7 % in TC degradation may be due to the strong electronic interaction between Ce and Mn in CeMO-7 %. This study not only offers a facile and high-efficiency methodology for the synthesis of two-dimensional nanomaterial, but also proposes a new idea for enhancing the removal of TC.

Hierarchical NiCo2S4@NiMoO4 nanotube arrays on nickel foam as an advanced bifunctional electrocatalyst for efficient overall water splitting

The development of efficient and robust electrocatalysts for overall water splitting (OWS) has a crucial effect on alleviating energy and environmental issues. Herein, an integrated electrode of hierarchical NiCo2S4 nanotube@NiMoO4 nanosheet arrays on nickel foam (NiCo2S4@NiMoO4/NF) is constructed via hydrothermal reaction. And the heterostructure can form the strong electron interaction and synergistic effect between NiCo2S4 and NiMoO4. Therefore, the NiCo2S4@NiMoO4/NF electrode exhibits prominent electrocatalytic performances with low overpotentials for oxygen and hydrogen evolution reaction (OER: 285 mV; HER: 197 mV) at the current density of 100 mA cm−2. Moreover, low potentials of 1.46, 1.63, and 1.75 V are needed to reach 10, 50, and 100 mA cm−2 and outstanding stability of 100 h is exhibited using NiCo2S4@NiMoO4/NF as a bifunctional electrocatalyst for OWS, which is superior over most of previously reported cobalt- and nickel-based electrocatalysts. These outstanding performances benefit from the unique hierarchical structure that combines the advantages of the nanosheet/nanotube and binder-free electrode, the specialty of NiCo2S4 and NiMoO4 in HER and OER, and the protective effect of the NiMoO4, which synergistically enhance the catalytic activity and stability of OWS.

Ferrocene Formic Acid Surface Modified Ni(OH)2 for Highly Efficient Alkaline Oxygen Evolution

FeNi-based hybrid materials are among the most representative catalysts for alkaline oxygen evolution reaction (OER), but the modulation of their surface atoms to achieve the optimal catalytic properties is still a big challenge. Here, we report the surface modification of Ni(OH)2/nickel foam (NF)-based electrocatalyst with a trace amount of ferrocene formic acid (FFA) (FFA-Ni(OH)2/NF) for highly efficient OER. Owing to the strong electron interaction and synergistic effects of Fe-Ni heteroatoms, FFA-Ni(OH)2/NF exhibits an overpotential of 311 mV at a current density of 100 mA cm−2. Impressively, the overpotential of FFA-Ni(OH)2/NF at 100 mA cm−2 is 108 mV less than that of bulk phase doped Ni/FFA(OH)2/NF, demonstrating the surprising effect of heteroatomic surface modification. In addition, by introducing a small amount of surface modifier into the electrolyte, the weak surface reconstruction process in the electrochemical process can be fully utilized to achieve obvious modification effects. Therefore, this work fully proves the feasibility of improving catalytic activities of FeNi-based catalysts by modifying surface heterogeneous atom pairs.

Dehydrogenation of hydrous hydrazine over carbon nanosphere- supported PtNi nanoparticles for on-demand H2 release

In despite of significant progresses have been accomplished in the programming and development of updated and efficient nana-catalysts for H2 production from a wide variety of chemical hydrogen storage materials. However, it is a practical matter of the utmost importance to develop the “on-off” control for on demand H2 release in the cause of effectively and safely producing, carrying and depositing H2 gas. Herein, we have first designed and synthesized a sequence of carbon nanosphere (CNS)-stabilized bimetallic PtNi nanoparticles (PtNi/CNS), by stabilization of nearly monodispersed PtNi bimetallic nanoparticles onto the surface of carbon nanosphere, for the highly selective and efficient on-demand H2 release upon the dehydrogenation of hydrous hydrazine. Then, the optional nanocatalyst Pt1Ni1/CNS exhibits the highest catalytic performance in hydrogen production from dehydrogenation of hydrous hydrazine, with 100 % H2 selectivity and the turnover frequency (TOF) of 3928 mol (H2)·molcat−1·h−1 at 50 °C. The detailed physical characterizations have confirmed that the superior catalytic performance of Pt1Ni1/CNS in the H2 release upon hydrous hydrazine dehydrogenation is attributed to the electronic interaction and synergistic effect between Ni and Pt. More importantly, the highly selective “on-off” control for demand-based H2 release upon the dehydrogenation of hydrous hydrazine is successfully realized by pH regulation.

Construction of a single-atom palladium catalyst by electronic metal-support interaction and interface confinement effect with remarkable performance in Suzuki coupling reaction

Atomically distributed metal catalysts with maximal atom utilization and distinctive catalytic properties have drawn attention in a variety of reactions. However, accessing excellent catalytic efficiency while preserving high stability is critical but challenging. Here we report a straightforward strategy by synergizing electronic metal-support interaction and interface confinement effect, which enables the precise construction of atomic palladium atoms supported over UiO-66-NH2. For the Suzuki coupling of bromobenzene with phenylboronic acid, this palladium catalyst demonstrates extraordinary catalytic performance in terms of activity (turnover frequency of 13043 h−1), selectivity (>99 %), and yield (>99 %). Additionally, it shows excellent recyclability, storage stability, and wide substrate scope. The experimental characterizations and DFT calculations demonstrate the high catalytic activity is attributed to the optimized electronic metal-support interactions and positive valence state of palladium atoms over the support. This study provides fundamental insights into the precise synthesis of single atom catalysts and their application in organic transformations.

Benchmarking collective effects of electron interactions in a wiggler with OPAL-FEL

OPAL-FEL is a recently developed tool for the modeling of particle accelerators containing wigglers or undulators. It extends the well established 3D electrostatic particle-tracking code OPAL, by merging it with the finite-difference time-domain electromagnetic solver MITHRA. We present results of two benchmark cases where OPAL-FEL simulations are compared to experimental results. Both experiments concern electron beamlines where the longitudinal phase space is modulated with a short magnetic wiggler. Good agreement was found in both the space charge and radiation dominated regimes.

Charge and energy transfer in ac-driven Coulomb-coupled double quantum dots

We study the dynamics of charge and energy currents in a Coulomb-coupled double quantum dot system, when only one of the two dots is adiabatically driven by a time-periodic gate that modulates its energy level. Although the Coulomb coupling does not allow for electron transfer between the dots, it enables an exchange of energy between them which induces a time variation of charge in the undriven dot. We describe the effect of electron interactions at low temperature using a time-dependent slave-spin 1 formulation within mean field that efficiently captures the main effects of the strong correlations as well as the dynamical nature of the driving. We find that the currents induced in the undriven dot due to the mutual friction between inter-dot electrons are of the same order as those generated in the adiabatically driven dot. Interestingly, up to 43% of the energy injected by the ac sources can be transferred from the driven dot to the undriven one. We complete our analysis by studying the impact of the Coulomb interaction on the resistance of the quantum dot that is driven by the gate.Graphic abstract

Exploiting the Synergistic Electronic Interaction between Pt-Skin Wrapped Intermetallic PtCo Nanoparticles and Co-N-C Support for Efficient ORR/EOR Electrocatalysis in a Direct Ethanol Fuel Cell.

The development of low-Pt catalysts with high activity and durability is critical for fuel cells. Here, Pt-skin wrapped sub-5nm PtCo intermetallic nanoparticles are successfully mounted on single atom Co-N-C support by exploiting the barrier effect of Co-anchor. According to a collaborative experimental and computational investigation, the increased oxygen reduction reaction activity of PtCo/Co-N-C arises from the direct electron transfer from PtCo to Co-N-C, and the resulting optimal d-band center of Pt. Owing to such unique electronic structure interaction and synergistic effect, the specific and mass activities of PtCo/Co-N-C are up to 4.20mA cm-2 and 2.71 A mgPt-1 , respectively, with barely degraded stability after 40 000 CV cycles. The PtCo/Co-N-C also exhibits outstanding activity as an ethanol electrocatalyst. This work shows a new and effective route to boost the overall efficiency of direct ethanol fuel cells in acidic media by integrating intermetallic low-Pt alloys and single atom carbon support.

Laser Control of Electronic Exchange Interaction within a Molecule.

Electronic interactions play a fundamental role in atoms, molecular structure and reactivity. We introduce a general concept to control the effective electronic exchange interaction with intense laser fields via coupling to excited states. As an experimental proof of principle, we study the SF_{6} molecule using a combination of soft x-ray and infrared (IR) laser pulses. Increasing the IR intensity increases the effective exchange energy of the core hole with the excited electron by 50%, as observed by a characteristic spin-orbit branching ratio change. This work demonstrates altering electronic interactions by targeting many-particle quantum properties.