Costate Research Articles

New heteroligand complex of cobalt with phthalocyanine, oxo and fluoro ligands: DFT consideration

Based on the results of a quantum chemical calculation using the DFT method in the OPBE/TZVP and B3PW91/TZVP levels, the possibility of the existence of a cobalt heteroligand complex containing in the inner coordination sphere tetra[benzo]derivative of porphyrazine (phthalocyanine), oxide (O[Formula: see text] and fluoride (F[Formula: see text] ions, with possible oxidation state of Co(V) that is non-characteristic for the given 3[Formula: see text]-element, has been shown. The data on the structural parameters, multiplicity of the ground state, NBO analysis data and standard thermodynamic parameters of formation (standard enthalpy [Formula: see text], entropy [Formula: see text] and Gibbs’s energy [Formula: see text] for the indicated complex have been presented. At the same time, it has been noted that the porphyrazine itself as well as di[benzo]porphyrazine, do not form such metalcomplexes.

Structural Changes in Monolayer Cobalt Oxides under Ambient Pressure CO and O2 Studied by In Situ Grazing-Incidence X-ray Absorption Fine Structure Spectroscopy.

We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.

Microwave-Assisted Coprecipitation Synthesis and Local Structural Investigation on NiO, β-Ni(OH)2/Co3O4 Nanosheets, and Co3O4 Nanorods Using X-ray Absorption Spectroscopy at Co-Ni K-edge and Synchrotron X-ray Diffraction.

Developing the most straightforward, cheapest, and eco-friendly approaches for synthesizing nanostructures with well-defined morphology having the highest possible surface area to volume ratio is challenging for design and process. In the present work, nanosheets of NiO and β-Ni(OH)2/Co3O4, and nanorods of Co3O4 have been synthesized at a large scale via the microwave-assisted chemical coprecipitation method under low temperature and atmospheric pressure. X-ray absorption spectroscopy (XAS) measurements, which comprises both X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques, have been carried out at Co and Ni K-edges to probe the electronic structure of the samples. Also, the local atomic structural, chemical bonding, morphological, and optical properties of the sample were systematically investigated using XAS, synchrotron X-ray diffraction (SXRD), Raman spectroscopy, FTIR, transmission electron microscopy (TEM), and UV–visible spectroscopy. The normalized XANES spectra of the β-Ni(OH)2/Co3O4 nanosheets show the presence of Ni2+ and a mixed oxidation state of Co. The disorder factor decreases from β-Ni(OH)2/Co3O4 to Co3O4 with increasing Co–O bond length. The SXRD pattern analyzed using Rietveld refinement reveals that NiO has a face-centered cubic phase, Co3O4 has the standard spinal structure, and β-Ni(OH)2/Co3O4 has a mixed phase of hexagonal and cubic structures. TEM images revealed the formation of nanosheets for NiO and β-Ni(OH)2/Co3O4 samples and nanorods for Co3O4 samples. FTIR and Raman spectra show the formation of β-Ni(OH)2/Co3O4, which reveals the fingerprints of Ni–O and Co–O.

First-principles investigation of (Co and N)-doped [formula omitted] for potential use in spintronic applications

The impact of cobalt and nitrogen on the structural, magnetic, and electronic properties of beryllium sulfur (BeS) is investigated in this work using the Korringa Kohn Rostoker (KKR) approach in conjunction with the coherent potential approximation (CPA) and the generalized gradient approximation (GGA). The density of states for Co and N doping indicates a half metallic (HM) behavior with a spin polarization reaching up to 100% at Fermi level. In addition, when increasing the concentration of dopants, the Curie temperature of BeS rises to maximum values of 494.66K and 691.80K for Co and N doped BeS respectively. The stability of the ferromagnetic order (FM) in these compounds is attributed to double-exchange interaction processes. According to our results, these new diluted materials show great potential for spintronic devices.

Local a posteriori error estimates for boundary control problems governed by nonlinear parabolic equations

We derive local a posteriori error estimates of finite element approximation to nonlinear parabolic boundary control problems in a bounded convex domain with Lipschitz boundary. We apply piecewise linear and continuous finite elements to approximate the state and co-state variables, and the control variable is approximated by using the piecewise constant functions. The discrete-in-time scheme is based on the backward Euler method. We derive a reliable type local a posteriori error estimates for Neumann boundary control problems in the L2([0,T];L2(∂Ω))-norm. The main feature of our estimators is that they are of local character in the sense that the leading terms of the estimators depend on the small neighbourhood of the boundary. These new local a posteriori error bounds can be used to study the behaviour of the state and co-state variables near the boundary. The derived error indicators will provide the necessary feedback for the adaptive mesh refinements in the finite element method. We report numerical tests to illustrate the effectiveness of our error indicators.

Systematic study of the effect of the co-solvent on the performance of amine-based solvents for CO2 capture

• Polar soft-SAFT predictive model are presented for CO 2 solubility in water-lean solvents. • Model parameters for absorption process accurately correlate with co-solvent dielectric constant. • Assessment of co-solvent effects on the CO 2 absorption process. • CO 2 solubility, degree of speciation, and enthalpy of absorption are obtained for all solvents. • Compared to aqueous amine, ethylene glycol is a promising co-solvent with acceptable trade-offs. Absorption and separation by aqueous amines is seen today as a mature technology for CO 2 capture at large scale. However, it still suffers from some drawbacks, especially the high energy required for the regeneration of the solvent. In this sense, water-free and water-lean solvents are attractive alternatives to replace them due to their potential in reducing this regeneration energy; however, systematic studies on the effect of the co-solvent on the required thermodynamic properties to optimize the separation process are still missing. In this work, we use the polar soft-SAFT equation of state for modeling CO 2 chemisorption in a range of aqueous, water-free, and water-lean solvents, formulated using glycol co-solvents. In addition to accurately capturing the CO 2 solubility in these solvents, the model allows to isolate the effect of a given organic diluent, and its ratio with water, on CO 2 solubility, degree of speciation, and enthalpy of absorption. We find that ethylene glycol is a promising co-solvent, as the reduction in CO 2 solubility is minimized, while exhibiting the largest decrease in enthalpy of absorption than other water-lean and water-free solvents, irrespective of the employed amine. This is the first study in which the effect of the co-solvent has been systematically evaluated at post-combustion capture conditions, helping in the rational design of novel solvents for CO 2 capture.

Elucidating Cathode Degradation Mechanisms in LiNi0.8Mn0.1Co0.1O2 (NMC811)/Graphite Cells Under Fast Charge Rates Using Operando Synchrotron Characterization

Li-ion batteries capable of extreme fast charging (XFC) are in demand to facilitate widespread electric vehicle (EV) adoption. While the impact of fast charge on the negative electrode has been studied, degradation of state-of-the-art NMC811 under XFC conditions has not been studied in detail. Herein, cathode degradation is probed in NMC811/graphite batteries by analysis of structural and chemical changes for recovered samples previously cycled under XFC conditions and during typical cycling. NMC surface reconstruction, as determined by soft X-ray absorption, was not detected for recovered electrodes. However, bulk redox activity from X-ray absorption near edge structure measurements showed more change in the oxidation state of Ni and Co under the 1C charge rate compared to the 4C rate consistent with the electrochemistry. Increased unit cell volume contraction under the 1C rate as determined by operando X-ray diffraction suggests that higher charge rates may provide a protective effect on the cathode by reducing structural distortion due to less delithiation.

Regulating electron transfer over asymmetric low-spin Co(II) for highly selective electrocatalysis

Modulating the steric-electronic configuration of metal-organic centers is key for tuning the activity and selectivity of heterogeneous reactions, especially multi-electron transfer reactions. Here, three different asymmetric metal-organic complexes with unique steric-electronic structures are immobilized on nanocarbon for an electron-transfer-controlled oxygen reduction reaction. The strong-field ligand-induced low-spin ( LS ) Co II creates a necessary steric configuration for regulating reaction selectivity through ligand's proton transfer ability, for which acidic diamine ligands facilitate a four-electron transfer (94%), whereas basic ligands drive a highly selective two-electron route (97%). The steric-electronic regulation of the reaction selectivity at catalytic sites is characterized using X-ray absorption spectroscopy, reaction kinetic path analysis, and density functional theory calculation. Our results indicate that an LS state of Co II with asymmetric coordination is necessary to form a unique “flytrap” structure to promote O 2 capture for the subsequent proton-coupled electron transfer, which is regulated by the Brønsted acidity of coordinating ligands. • A series of asymmetric metal-organic complexes are immobilized on nanocarbons • Advanced characterizations are used to explore their structures at the atomic level • Selectivity of ORR is regulated by changing the ligand field strength of the active site • Operando X-ray spectroscopy and computational analysis confirm the reaction mechanism The majority of energy conversion processes such as hydrogen peroxide production, nitrogen fixation, and CO 2 reduction generally involve multi-electron transfer, resulting in multiple by-products and requiring tedious purification process. The development of highly selective electrocatalysts can not only reduce the energy consumption in the production process but also benefit to promote their large-scale application. Here, we report an asymmetric ligand design of molecular “Venus flytrap” at atomic Co II catalysts on a heterogeneous carbon surface for oxygen electrocatalysis with controlled selectivity. Our XAFS and DFT calculations show that the strong-field ligand-induced LS Co II centers offer inimitable steric-electronic advantages in capturing O 2 and the capability to regulate reaction pathways through an H-bonding interaction between the ligands and peroxo intermediate. The proposed concept completes the picture of designer single-atom catalyst by covering the often overlooked exterior coordination sites, and is expected to be generally applicable to other heterogeneous catalyst systems. Steric-electronic configuration regulation plays a key role in achieving highly selective electrocatalysis. As a proof of concept, a series of asymmetric metal-organic complexes were immobilized on a conductive substrate for oxygen reduction reaction (ORR). The strong-field ligand-induced low-spin cobalt sites exhibit an excellent selectivity for four-electron ORR, whereas the medium-field ligand linked Co sites display high efficiency for the two-electron reduction of oxygen into hydrogen peroxide.

Low energy inelastic electron scattering from carbon monoxide: II. Excitation of the b3Σ+, j3Σ+, B1Σ+, C1Σ+ and E1Π Rydberg electronic states

In this second part of a two part paper (first part: Zawadzki et al (2020 J. Phys. B: At. Mol. Opt. Phys. 53 165201)) we present differential scattering cross sections for excitation of several Rydberg electronic states of carbon monoxide by electron impact. The first part concerned the low-lying valence states of CO. In the present study cross sections are obtained experimentally using low-energy electron energy-loss spectroscopy and theoretically using the R-matrix method. Incident electron energies range from near-threshold of 12.5 eV to 20 eV while the scattering angles range from 20° to 120°. The R-matrix calculations use three distinct close-coupling models and their results are compared to available experimental and theoretical cross sections. The overall comparison leads to significantly improved description of the excitation cross sections for this target.

Generation of hyperentangled states and two-dimensional quantum walks using J or q plates and polarization beam splitters

A single photon can be made to entangle simultaneously in its different internal degrees of freedom (DoF)---polarization, orbital angular momentum (OAM), and frequency---as well as in its external DoF---path. Such entanglement in multiple DoF is known as hyperentanglement and provides additional advantage for quantum information processing. We propose a passive optical setup using $q$ plates and polarization beam splitters to hyperentangle an incoming single photon in polarization, OAM, and path DoF. By mapping polarization DoF to a two-dimensional coin state, and path and OAM DoF to two spatial dimensions, $x$ and $y$, we present a scheme for realization of a two-dimensional discrete-time quantum walk using only polarization beam splitters and $q$ plates ensuing the generation of hyperentangled states. The amount of hyperentanglement generated is quantified by measuring the entanglement negativity between any two DoF. We further show that hyperentanglement generation can be controlled by using an additional coin operation or by replacing the $q$ plate with a $J$ plate.

Electronic Structure of Excited States in Co

Electronic Structure of Excited States in Co

NEXAFS and FTIR Spectroscopy of Co-doped SrBi2Nb2O9

The solid-phase ceramic method was used to synthesize cobalt-containing solid solutions based on SrBi2Nb2O9. NEXAFS (Near Edge X-ray Absorption Fine Structure) and IR spectroscopy were used to study the electronic state of cobalt atoms in solid cross-links with a layered perovskite-like structure. It was found that cobalt atoms are in high-spin states of Co(III) and, mainly, Co(II) in an octahedral oxygen environment

Identification the Effect of Coordination States of Co on Co-Nx Co-Doped Graphene for Selective Oxidation of H2s: A Dft Study

Identification the Effect of Coordination States of Co on Co-Nx Co-Doped Graphene for Selective Oxidation of H2s: A Dft Study

Multipoint flux mixed finite element method for parabolic optimal control problems

<abstract><p>In this paper, we research semi-discrete multipoint flux mixed finite element (MFMFE) method for parabolic optimal control problem (OCP). The state and co-state variables are approximated by the lowest order Brezzi-Douglas-Marini (BDM) mixed finite element (MFE) spaces and the control is approximated by piecewise constant. The advantage of this type of mixed element method is that it can decouple the state and adjoint state variables as cell-centered difference schemes rather than to solve saddle point algebraic equations. Error estimates and convergence orders are derived rigorously for state and control variables. Finally, a numerical example is given to confirm our theoretical analysis.</p></abstract>

Reconfiguration Optimization of Relative Motion Between Elliptical Orbits Using Lyapunov-Floquet Transformation

This paper investigates the reconfiguration optimization of the formation flying in elliptical orbits. Based on the Tschauner-Hempel equations, the time-varying system has been reduced to a time-independent one by Lyapunov-Floquet transformation without losing its relative motion characteristics. A geometric configuration invariant of the formation is introduced and general relative configurations are considered as linear combinations of essential components in proportion to this invariant. Benefitting from the evolution of the configuration invariant, the reconfiguration optimization is converted into an optimal parameter selection problem and the transfer trajectory is parameterized by a functional integral. In particular, the indirect method of optimal control based on the reduced dynamics avoids the time-varying derivative of costate variables, which simplifies the optimization problem. The numerical results of both low-thrust and impulsive reconfigurations verify the effectiveness of the reconfiguration optimization based on the reduced relative dynamics.

Near-optimal control of a stochastic SICA model with imprecise parameters

An adequate near-optimal control problem for a stochastic SICA (Susceptible-Infected-Chronic-AIDS) compartmental epidemic model for HIV transmission with imprecise parameters is formulated and investigated. We prove some estimates for the state and co-state variables of the stochastic system. The established inequalities are then used to prove a necessary and a sufficient condition for near-optimal control with imprecise parameters. The proofs involve several mathematical and stochastic tools, including the Burkholder-Davis-Gundy inequality.

The Regulation of O2 Spin State and Direct Oxidation of CO at Room Temperature Using Triboelectric Plasma by Harvesting Mechanical Energy.

Oxidation reactions play a critical role in processes involving energy utilization, chemical conversion, and pollutant elimination. However, due to its spin-forbidden nature, the reaction of molecular dioxygen (O2) with a substrate is difficult under mild conditions. Herein, we describe a system that activates O2 via the direct modulation of its spin state by mechanical energy-induced triboelectric corona plasma, enabling the CO oxidation reaction under normal temperature and pressure. Under optimized reaction conditions, the activity was 7.2 μmol h−1, and the energy consumption per mole CO was 4.2 MJ. The results of kinetic isotope effect, colorimetry, and density functional theory calculation studies demonstrated that electrons generated in the triboelectric plasma were directly injected into the antibonding orbital of O2 to form highly reactive negative ions O2−, which effectively promoted the rate-limiting step of O2 dissociation. The barrier of the reaction of O2− ions and CO molecular was 3.4 eV lower than that of O2 and CO molecular. This work provides an effective strategy for using renewable and green mechanical energy to realize spin-forbidden reactions of small molecules.

Tunable Single-Atomic Charges on a Cleaved Intercalated Transition Metal Dichalcogenide.

Control of a single ionic charge state by altering the number of bound electrons has been considered as an ultimate testbed for atomic charge-induced interactions and manipulations, and such subject has been studied in artificially deposited objects on thin insulating layers. We demonstrate that an entire layer of controllable atomic charges on a periodic lattice can be obtained by cleaving metallic Co1/3NbS2, an intercalated transition metal dichalcogenide. We identified a metastable charge state of Co with a different valence and manipulated atomic charges to form a linear chain of the metastable charge state. Density functional theory investigation reveals that the charge state is stable due to a modified crystal field at the surface despite the coupling between NbS2 and Co via a1g orbitals. The idea can be generalized to other combinations of intercalants and base matrices, suggesting that they can be a new platform to explore single-atom-operational 2D electronics/spintronics.

Cobalt oxide decorated porous silica particles: Structure and activity relationship in the catalytic oxidation of carbon monoxide

Porous (0.6–30 nm) and non-porous spherical silica nanoparticles are synthesized. These silicas with different morphologies are decorated with cobalt (2.9 wt%) using Co(NO3)2·6H2O as precursor. Co-SiO2 particles are studied by N2 sorption, TEM, XRD, XPS, FTIR and TPR-H2 methods. Specific surface area (SSA) of the prepared materials is 10–1200 m2/g. The main crystalline phase is identified as Co3O4. The activity of Co-SiO2 composites in the CO oxidation and preferential oxidation of CO (PROX) in a H2-rich gas mixture improves with increasing atomic ratios of Co/Si and Co3+/Co2+ on the silica surface. Catalysts with the large mesopores containing mainly Co2+ are the least active. Co-SiO2 composites based on synthetic opal grown by sedimentation of non-porous silica particles with the lowest SSA demonstrate the highest catalytic activity. The CO conversion reaches 100% at 150 °C in the absence of hydrogen, while in PROX the 90% conversion of CO is achieved at 170 °C. The large Co3O4 aggregates between non-porous spherical silica particles of opal are the most active and stable during CO-PROX reaction. The lower interaction of Co3O4 nanoparticles with this support promotes the stabilization of the oxidized state Co3+ and provides a higher yield of CO2 in CO-PROX reaction.

Calculation of electric quadrupole linestrengths for diatomic molecules: Application to the H2, CO, HF, and O2 molecules.

We present a unified variational treatment of the electric quadrupole (E2) matrix elements, Einstein coefficients, and linestrengths for general open-shell diatomic molecules in the general purpose diatomic code Duo. Transformation relations between the Cartesian representation (typically used in electronic structure calculations) to the tensorial representation (required for spectroscopic applications) of the electric quadrupole moment components are derived. The implementation has been validated against accurate theoretical calculations and experimental measurements of quadrupole intensities of 1H2 available in the literature. We also present accurate electronic structure calculations of the electric quadrupole moment functions for the X1Σ+ electronic states of CO and HF, as well as for the a1Δg-b1Σg + quadrupole transition moment of O2 with the MRCI level of theory. Accurate infrared E2 line lists for 12C16O and 1H19F are provided. A demonstration of spectroscopic applications is presented by simulating E2 spectra for 12C16O, H19F, and 16O2 (Noxon a1Δg-b1Σg + band).