Electron Exchange Processes Research Articles

Promoting electrochemical conversion of CO2 to formate with rich oxygen vacancies in nanoporous tin oxides

Defect engineering, especially oxygen vacancies (O-vacancies) introduction into metal oxide materials has been proved to be an effective strategy to manipulate their surface electron exchange processes. However, quantitative investigation of O-vacancies on CO2 electroreduction still remains rather ambiguous. Herein, a series of nanoporous tin oxide (SnOx) materials have been prepared by thermal treatment at various temperatures and reaction conditions. The annealing temperature dependent O-vacancies property of the SnOx was revealed and attributed to the balance tunning of the desorption of oxygen species and the continous oxidation of SnOx. The as-prepared nanoporous SnOx with 300 °C treatment was found to be highest O-vacant material and showed an impressive CO2RR activity and selectivity towards the conversion of CO2 into formic acid (up to 88.6%), and superior HCOOH incomplete current density to other samples. The ideal performance of the O-vacancies rich SnOx-300 material can be ascribed to the high delocalized electron density inducing much enhanced adsorption of CO2 with O binding and benefiting the subsequent reduction with high selectively forming of formic acid.

Electrochemical Energy Storage of Ni-Doped Metal Organic Framework and Reduced Graphene Oxide Composites

Metal Organic Frameworks (MOFs) are crystalline, open-porous materials consisting of metal ions or metal-oxo units coordinated by electron donating organic ligands and possess very high surface area, well defined pore sizes, tailorable structure and permeability to guest molecules. MOFs have been widely used in catalysis, gas separation, drug storage and delivery, imaging and sensing, optoelectronics and molecular sieving. Although these chemical building blocks can participate in electron exchange processes with the likelihood of providing rich fundamental data; utilizing these materials for energy storage application have been limited. In the present study, composites of a Ni-doped MOF with reduced graphene Oxide (rGO) are synthesized in bulk (gram scale) quantities. The composites are composed of rGO sheets which avoid restacking from the physical presence of MOF crystals. Ni in Ni-doped MOF is found to engage in a reversible, efficient, redox reaction shuttling between Ni and Ni(OH)2 in aqueous potassium hydroxide (KOH) electrolyte. Employing electrochemical impedance spectroscopy, we determined the charge transfer resistance to be 184 mΩ for MOF, 74 mΩ for a Ni doped MOF and 6 mΩ for an rGO-Ni-doped MOF composite, but these modifications do not affect the mass transfer resistance. This redox reaction in conjunction with the lowered charge transfer resistance from the introduction of rGO underpin the synergy which dramatically increases the capacitance to 758 F/g in the rGO-Ni-doped MOF composite, when the parent MOF could store only 100 F/g and a physical composite of rGO and Ni-doped MOF could algebraically achieve about 240 F/g. A generic approach of doping MOFs with a redox active metal and forming a composite with rGO transforms an electro-inactive MOF to high capacity energy storage material with energy density of 37.8 Wh/kg at a power density of 227 W/kg. These results can promote the development of high performance energy storage materials from the wide family of MOFs available.

Electron exchange between neutral and ionized impurity iron centers in vitreous arsenic selenide

Impurity iron atoms in vitreous arsenic-selenide As2Se3 films modified by iron form one-electron donor centers with an ionization energy of 0.24 (3) eV (the energy is counted from the conduction-band bottom). The Fermi level is shifted with an increase in the iron concentration from the mid-gap to the donorlevel position of iron due to the filling of one-electron states of the acceptor type lying below the Fermi level. At an iron concentration of ≥3 at %, the electron-exchange process is observed between neutral and ionized iron centers resulting in a change both in the electron density and in the tensor of the electric-field gradient at iron-atom nuclei with increasing temperature above 350 K.

Two-electron exchange between impurity centers of tin in PbS z Se1–z solid solutions

Using emission Mossbauer spectroscopy on 119mmSn(119mSn) and 119Sb(119mSn) isotopes, the electron exchange process between neutral and doubly ionized U – tin centers is studied in partially compensated PbS z Se1–z solid solutions. The activation energy of this process for compositions with z ≈ 1 is comparable to the deposition depth of the tin energy levels in the band gap of PbS (~0.11(1) eV, and for compositions with z ≈ 1, it is comparable with the correlation energy of donor U – tin centers in PbSe (~0.05(1) eV). For all compositions of solid solutions, the exchange is realized by the simultaneous transfer of two electrons with the use of the delocalized states of the valence band.

Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot.

We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time.

Ligand π-radical interaction with f-shell unpaired electrons in phthalocyaninato-lanthanoid single-molecule magnets: a solution NMR spectroscopic and DFT study.

The phthalocyaninato double-decker complexes [M(obPc)2 ](0) (M= Y(III) , Tb(III) , Dy(III) ; obPc=2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato), along with their reduced ([M(obPc)2 ](-) [P(Ph)4 ](+) ; M=Tb(III) , Dy(III) ) and oxidized ([M(obPc)2 ](+) [SbCl6 ](-) (M=Y(III) , Tb(III) ) counterparts were studied with (1) H, (13) C and 2D NMR. From the NMR data of the neutral (i.e., with one unpaired electron in the ligands) and anionic Tb(III) complexes, along with the use of dispersion corrected DFT methods, it was possible to separate the metal-centered and ligand-centered contributions to the hyperfine NMR shift. These contributions to the (1) H and (13) C hyperfine NMR shifts were further analyzed in terms of pseudocontact and Fermi contact shifts. Furthermore, from a combination of NMR data and DFT calculations, we have determined the spin multiplicity of the neutral complexes [M(obPc)2 ](0) (M=Tb(III) and Dy(III) ) at room temperature. From the NMR data of the cationic Tb(III) complex, for which actually no experimental structure determination is available, we have analyzed the structural changes induced by oxidation from its neutral/anionic species and shown that the interligand distance decreases upon oxidation. The fast electron exchange process between the neutral and anionic Tb(III) double-decker complexes was also studied.

Electrochemically and Chemically Induced Redox Processes in Molecular Machines

AbstractThe controlled motion of ions, molecules, or supramolecular entities has inspired scientists for more than 25 years, and the concept remains of great interest for the development of moveable nanoscale objects for applications in electronics, medicine, and materials chemistry. Artificial molecular machines that involve electron exchange processes induced by electrical, chemical, or photochemical energy, have been widely developed. More specifically, machines that are stimulated by electrochemical means have been the focus of particular attention because such systems can allow the change of states to be followed and can enable access to mechanistic pathways through direct monitoring. Furthermore, these devices have the ability to connect the nanoscale machine to the macroscopic world, for instance by surface immobilization. In this review, we report recent examples of redox‐based molecular machines in both fluid solution and in organized or controllable environments such as modified electrodes, nanoparticles, polymers, gels, and liquid crystals. Basic concepts of molecular machinery and general applications are also discussed.

Model-driven standardization of public authority data interchange

In the past decade, several electronic data exchange processes between public authorities have been established by the German public administration. In the context of various legacy systems and numerous suppliers of software for public authorities, it is crucial that these interfaces are open and precisely and uniformly defined, in order to foster free competition and interoperability. A community of such projects and specifications for various public administration domains has arisen from an early adopter project in the domain of data interchange between the 5400 German municipal citizen registers. A central coordination office provides a framework for these projects that is put into operation by a unified model-driven method, supported by tools and components, involving UML profiles, model validation, and model-to-text transformations into several technical domains. We report how this model-driven approach has already proven to be effective in a number of projects, and how it could contribute to the development of standardized e-government specifications in various ways.

Influence of applied pressure on the probability of electronic energy transfer across a molecular dyad

A pair of covalently linked molecular dyads is described in which two disparate boron dipyrromethene dyes are separated by a tolane-like spacer. Efficient electronic energy transfer (EET) occurs across the dyad; the mechanism involves important contributions from both Förster-type coulombic interactions and Dexter-type electron exchange processes. The energy acceptor is equipped with long paraffinic chains that favor aggregation at high concentration or at low temperature. The aggregate displays red-shifted absorption and emission spectral profiles, relative to the monomer, such that EET is less efficient because of a weaker overlap integral. The donor unit is insensitive to applied pressure but this is not so for the acceptor, which has extended π-conjugation associated with appended styryl groups. Here, pressure reduces the effective π-conjugation length, leading to a new absorption band at higher energy. With increasing pressure, the overall EET probability falls but this effect is nonlinear and at modest pressure there is only a small recovery of donor fluorescence. This situation likely arises from compensatory phenomena such as restricted rotation and decreased dipole screening by the solvent. However, the probability of EET falls dramatically over the regime where the π-conjugation length is reduced owing to the presumed conformational exchange. It appears that the pressure-induced conformer is a poor energy acceptor.

Anisotropy and charge effect in collisions of ions with biomolecules

Charge transfer dynamics induced by collision of carbon ions with biological targets has been investigated theoretically by means of ab-initio quantum chemistry molecular methods. The series of pyrimidine nucleobases, thymine, uracil and 5-halouracil with similar skeleton and different substituents have been considered. The charge effect between C6+ and C4+ carbon ions is analyzed as well as the anisotropy of the electron exchange process.

Electronic information exchange between emergency departments and poison control centers: A Delphi study

Context. The US emergency departments and poison control centers use telephone communication to exchange information about poison exposed patients. Electronically exchanged patient information could better support care for poisoned patients by improving information availability for decision making and by decreasing unnecessary emergency department telephone interruptions. As federal initiatives push to increase clinical health information exchange (HIE), it is essential to assess the readiness of US poison control centers. We conducted a nationwide Delphi study to determine consensus on legal, operational, and clinical considerations that are important for electronic information exchange between emergency departments and poison control centers. Materials and methods. A national panel of US experts (n = 71) in emergency medicine and poison control participated in a Delphi study, September–December 2010. Panelists rated statements describing concepts related to implementation, adoption, or potential outcomes of electronic information exchange between emergency departments and poison control centers. The statements reflected panelist responses to initial open-ended questions and literature-based concepts. Results. A total of 71 panelists agreed to participate. The response rate for each round ranged from 0.73 to 0.77. Most (114/121) statements reached consensus. Seven statements failed to reach consensus. Panelists indicated that user involvement in the design of systems and tools is important. Workflow integration, safety, evidence of benefit, and outcomes are high-importance issues. Discussion/conclusions. Future research and development related to electronic information exchange should address high-importance issues: safety, patient outcomes, workflow integration, and evidence of benefit. It should also address key barriers: initial and ongoing costs associated with electronic information exchange, the absence of software and tools to facilitate exchange, and the need for training. Users should be involved in the design of an electronic information exchange process, and the process should support, not replace, verbal communication.

Singlet-Triplet Switching Induced by Electric Field in Triple Quantum Dots

We analyze in uence of an external electric eld on magnetic properties of a triple quantum dot system in a triangular and linear geometry. The system contains four electrons and is described by an extended Hubbard model which includes electron correlations and exchange processes. The electric eld leads to splitting of energy levels (the Stark e ect) and to transition between the singlet and triplet states.

Value Creation in Electronic Supply Chains by Adoption of a Vendor Managed Inventory System

Many strategies have been developed to manage supply chain operations effectively. Vendor Managed Inventory (VMI) system is one of the prevalent strategic tools of the supply side logistics based on the electronic data exchange and business process automation among the suppliers and customers to enhance the competitive advantage. VMI is widely used in different industries including automotive sector. The VMI concept is a continuous replenishment program where suppliers are given access to demand and inventory level of customers and they are fully responsible for managing and replenishing the customer’s stock. VMI’s extension on customer satisfaction cannot be perceived sufficiently by decision-makers who are responsible to develop and invest in the customer-supplier relationship. This paper presents a path model using the method of Partial Least Squares (PLS) regression to give insight to decision-makers to understand effect of the VMI adoption on customer satisfaction. This paper investigates both determinants of relative factors of successful VMI adoption and the relationship in the supply chain with an empirical automotive industry case. The results show that the collaboration and coordination between customer and supplier and infrastructure of the information-sharing are the important dimensions to add value to the supply chain and to enhance customer satisfaction.

Atomic Alignment Effect in the Dissociative Energy Transfer Reaction of Metal Carbonyls (Fe(CO)5, Ni(CO)4) with Oriented Ar (3P2, MJ = 2)

The atomic alignment effect has been studied for the dissociative energy transfer reaction of metal carbonyls (Fe(CO)(5), Ni(CO)(4)) with the oriented Ar ((3)P(2), M(J) = 2). The emission intensity from the excited metal products (Fe*, Ni*) has been measured as a function of the atomic alignment in the collision frame. The selectivity of the atomic orbital alignment of Ar ((3)P(2), M(J) = 2) (rank 2 moment, a(2)) is found to be opposite for the two reaction systems; the Fe(CO)(5) reaction is favorable at the Π configuration (positive a(2)), while the Ni(CO)(4) reaction is favorable at the Σ configuration (negative a(2)). Moreover, a significant spin alignment effect (rank 4 moment, a(4)) is recognized only in the Ni(CO)(4) reaction. The atomic alignment effect turns out to be essentially different between the two reaction systems; the Fe(CO)(5) reaction is controlled by the configuration of the half-filled 3p atomic orbital of Ar ((3)P(2)) in the collision frame (L dependence), whereas the Ni(CO)(4) reaction is controlled by the configuration of the total angular moment J (including spin) of Ar ((3)P(2)) in the collision frame (J dependence). As the origin of J dependence observed only in the Ni(CO)(4) reaction, the correlation (and/or the interference) between two electron exchange processes via the electron rearrangements is proposed.

Fluctuation theorem and microreversibility in a quantum coherent conductor

Mesoscopic systems provide us a unique experimental stage to address non-equilibrium quantum statistical physics. By using a simple tunneling model, we describe the electron exchange process via a quantum coherent conductor between two reservoirs, which yields the fluctuation theorem (FT) in mesoscopic transport. We experimentally show that such a treatment is semi-quantitatively validated in the current and noise measurement in an Aharonov-Bohm ring. The experimental proof of the microreversibility assumed in the derivation of FT is presented.

Diamond-Like Carbon produced by highly charged ions impact on highly oriented pyrolytic graphite

The formation of Diamond-Like Carbon (DLC) structure on the surface of Highly Oriented Pyrolytic Graphite (HOPG) following Xe q+ (q = 5 ∼ 26) ions irradiation with different fluence is studied with Raman and X-ray photoelectron spectroscopy (XPS) analyses in this work. The DLC structure formed on HOPG is shown by the electronic structure transition from sp 2 to sp 3 hybridization. An obvious evolution of the transition depending on the charge state and the fluence of the impact ions were found. The DLC production is considered to be caused by both kinetic energy and potential energy deposition, the surface structure could be strongly changed due to high-density energy deposition and the intense inelastic electronic energy exchange process.

Sensitizing the Sensitizer: The Synthesis and Photophysical Study of Bodipy−Pt(II)(diimine)(dithiolate) Conjugates

The dyads 3, 4, and 6, combining the Bodipy chromophore with a Pt(bpy)(bdt) (bpy = 2,2'-bipyridine, bdt = 1,2-benzenedithiolate, 3 and 6) or a Pt(bpy)(mnt) (mnt = maleonitriledithiolate, 4) moiety, have been synthesized and studied by UV-vis steady-state absorption, transient absorption, and emission spectroscopies and cyclic voltammetry. Comparison of the absorption spectra and cyclic voltammograms of dyads 3, 4, and 6 and those of their model compounds 1a, 2, 5, and 7 shows that the spectroscopic and electrochemical properties of the dyads are essentially the sum of their constituent chromophores, indicating negligible interaction of the constituent chromophores in the ground state. However, emission studies on 3 and 6 show a complete absence of both Bodipy-based fluorescence and the characteristic luminescence of the Pt(bpy)(bdt) unit. Dyad 4 shows a weak Pt(mnt)-based emission. Transient absorption studies show that excitation of the dyads into the Bodipy-based (1)ππ* excited state is followed by singlet energy transfer (SEnT) to the Pt(dithiolate)-based (1)MMLL'CT (mixed metal-ligand to ligand charge transfer) excited state (τ(SEnT)(3) = 0.6 ps, τ(SEnT)(4) = 0.5 ps, and τ(SEnT)(6) = 1.6 ps), which undergoes rapid intersystem crossing to the (3)MMLL'CT state due to the heavy Pt(II) ion. The (3)MMLL'CT state is then depopulated by triplet energy transfer (TEnT) to the low-lying Bodipy-based (3)ππ* excited state (τ(SEnT)(3) = 8.2 ps, τ(SEnT)(4) = 5 ps, and τ(SEnT)(6) = 160 ps). The transition assignments are supported by TD-DFT calculations. Both energy-transfer processes are shown to proceed via a Dexter electron exchange mechanism. The much longer time constants for dyad 6 relative to 3 are attributed to the significantly poorer coupling and resonance of charge-separated species that are intermediates in the electron exchange process.

Glassy carbon perceived as graphitized material. Cathodic charge and reactivity toward alkyl halides. A new concept in surface modifications of carbons

Glassy carbon was reported to be efficient in two-electron reductive scission of alkyl halides RX for leading to RH. When organic solvents are used, it is shown that, within the potential range [−1.5V to −3V], the electrochemical process is complicated to a large extend by the progressive alkylation of the carbon surface until the formation of compact films composed of immobilized alkyl groups. It is proposed that behaviour be related to the presence of graphitized zones at the glassy carbon surface. These large zones of sp2 carbons can be transformed under electrochemical charge into nucleophilic belts for reacting towards RXs via a kind of heterogeneous SN2. This interfacial process independently coexists with that governed by electron transfers (ET). Therefore, the nature of the scission (pure electron exchange process) with the transient formation of a radical R, should be re-considered according to the real reactivity of the carbon surface, the electrophilicity of the RX and the applied potential. Additionally, this simple procedure may lead to an efficient way for grafting alkyl links and tagging to their extremity several chemical functions.

Atom transfer and electron exchange processes with cobalt complexes

The results of some investigations of several redox processes involving cobalt complexes are presented. For the first group of reactions below, oxidation appears to be accomplished in a single act by the direct addition of the oxidizing atom or group to the cobaltous complex: On the other hand, cases studied which appear to involve an electron transfer type of process include: (1) Co(CN)5−3+Fe(CN)6−3+H2O= [Co(CN)5(H2O)]−2+Fe(CN)6−4 (2) Co(C2O4)3−4+Ce(IV)=Co(C2O4)5−3+Ce(III) (3) CoV−2+Fe(CN)5−3=CoV−1+Fe(CN)6−4 (V=ethylene diaminetetracetate) (4) Co*(C2O4)3−4+Co(C2O4)3−3 = exchange (5) Co V−2+Co*V−1 = exchange Reactions of the first type are generally faster than those of the second, and possible explanations are discussed, along with some details of the kinetics of the reactions and a description of the several new complexes involved. In particular, an examination of the energy level diagrams predicted by Crystal Field Theory provides some explanation of the slowness of the electron transfer processes.

Remote Sensitized Photoisomerization via Through‐Bond Triplet–Triplet Energy Transfer Mediated by a Salt Bridge in a Supramolecular Dyad

A supramolecular dyad, BP-(amidinium-carboxylate)-NBD is constructed, in which benzophenone (BP) and norbornadiene (NBD) are connected via an amidinium-carboxylate salt bridge. The photophysical and photochemical properties of the assembled BP-(amidinium-carboxylate)-NBD dyad are examined. The phosphorescence of the BP chromophore is efficiently quenched by the NBD group in BP-(amidinium-carboxylate)-NBD via the salt bridge. Time-resolved spectroscopy measurements indicate that the lifetime of the BP triplet state in BP-(amidinium-carboxylate)-NBD is shortened due to the quenching by the NBD group. Selective excitation of the BP chromophore results in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that the triplet-triplet energy transfer occurs efficiently in the BP-(amidinium-carboxylate)-NBD salt bridge system. The triplet-triplet energy transfer process proceeds with efficiencies of approximately 0.87, 0.98 and the rate constants 1.8x10(3) s(-1), and 1.3x10(7) s(-1) at 77 K and room temperature, respectively. The mechanism for the triplet-triplet energy transfer is proposed to proceed via a "through-bond" electron exchange process, and the non-covalent bonds amidinium-carboxylate salt bridge can mediate the triplet-triplet energy transfer process effectively for photochemical conversion.